Infrared Heaters

Infrared Heater Buyer's Guide

There's nothing quite like the pleasant, all-over, open-air warmth you get at the beach or from an infrared heater. Yet, somehow, most of our attempts to keep warm center around trapping ourselves inside boxes of hot air. What if there were a way to break out and have that beach warm sensation wherever and whenever you wanted it? And what if heating outside that box literally helped you breathe easier and use less energy?

Well, that's exactly what Infrared Heaters can help you do. And the reason they can is that they don't bother trying to heat air.

What are infrared (IR) heaters?

Have you ever stood under the covered porch of a luxury hotel in winter without feeling cold? Or, have you ever felt heat at an indoor hockey game even though the ice wasn't melting? Then you've experienced the wonder of infrared heaters. Infrared heaters can heat venues inside stadium arenas from 170 feet away. That's because they don't heat the air in the space, they heat immovable objects. In the last 10-15 years, manufacturers cranked out dozens of models of these appliances, so you can harness the power of infrared heat in any room you'd like, indoors and out.

Who will infrared heaters appeal to?

Areas you may have thought of as off-limits or hard to heat are accessible with infrared heaters. Rooms with high ceilings, garages, and other semi-insulated spaces are all great candidates. Likewise, conservatories, four-season rooms, and outdoor spaces are also great.

On the true interior of your building, providing heat only where necessary becomes much more practical. And, it works whether you want a well-executed zone heating or you've always wanted a dedicated space for yoga.

Infrared heater for a yoga studio

People with allergies or other breathing problems report preferring heat provided by infrared. It's one reason infrared heating is the method of choice for hospitals like the U.S. Veteran's Association Hospitals.

Designers love infrared heaters for the floor plan creativity they allow. And the technology is even growing in popularity with building engineers. They find it a perfect marriage for sustainable HVAC systems powered by renewable energy sources.

Users of infrared heaters tend to notice a few advantages right off the bat. First, well-placed infrared warms people and things in the room directly. A whole room doesn't have to warm up before a person feels comfortable. The heat hits its target almost the moment the heater turns on. It also means that when a door opens or a draft blows through, all the heat isn't "lost." Things return to normal much faster.

Second, warming up doesn't need air circulation, so fewer allergens or irritants linger in the air. This isn't only true of dust and pollen on the surfaces in a room, either. Forced air filters and ducts trap dust over time. So, the less often people use their blowers, the happier their eyes, noses, and throats seem to be.

Third, people in many studies say that heat from the right infrared heater feels better. In winter, there's less of the dried out feeling that comes from using a furnace. The heating action can be directed to stay in the first 6 to 8 feet of height in the room, where it's actually needed. Plus, one of the most overlooked issues in maintaining body heat can be corrected with the right infrared setup. (We take a look at this in the technical section below.)

Saving money in a jar

Over the long run, avid and shrewd infrared users end up with more money in their pockets, too. Air acts like a middleman collecting a non-stop energy fee to get heat where you want it. Infrared helps reduce its take. Combining that with zone management has been confirmed by study after study to lower energy consumption, and thus costs. They also have some of the lowest overall lifetime costs of ownership of any type of heating appliance.

Further down the line, there are even health benefits to be had as well. When you heat floors and walls with infrared appliances, you can reduce mold and dust mites.

In the end, infrared heaters may help you get more enjoyment out of the space you're in. Indoors they have the potential to free users from the confines of conventional forced-air heating. And outdoors, they can add up to 100 more usable nights per year to space.

Before You Buy

When you install any major appliance, there are "official" considerations to make before you buy. We'll cover the features of different types of infrared heaters later to help you narrow down the one(s) for you. But this section will cover the regulatory side of deciding what to buy.

Utility Considerations

Infrared heaters have fewer regulations. But, it's good to know what local building authority restrictions might affect your plans. We'll see later that infrared heaters can run on either gas or electricity. So, before you buy an appliance, you'll want to check possible limitations for your "fuel source."

For instance, if you're planning to install an electric heater, verify amperage and voltage needs for the unit. This might require consulting with your electricity provider and a knowledgeable electrician.

Electrician hooking up electrical components

If you're planning to run a gas appliance, check with a gas plumber and your local gas provider. Whether you plan to use natural gas or liquid propane, you'll need to provide adequate gas pressure to the unit. You'll also want to estimate the consumption rate.

AHJ Considerations

Plug-in appliances don't typically need any special permitting from a local code office. But, gas appliances may be different. Appliances hardwired for electricity as permanent fixtures may need one, too. Commercial installations often call for special permits. So, check with your local building authority or other authority having jurisdiction (AHJ). Also, check with your AHJ if you're planning to install heaters as part of a renovation or addition.

Local authorities start with national standards, or "codes," as a foundation. They have the right, though, to make changes or adjustments as needed in their areas. Your AHJ always has the final word. What it says, goes. And, what's required can vary quite a bit from place to place. So, there's no getting around checking with your local code office.

Code, Certification, and Listing Agencies

Several agencies publish performance and safety standards for manufacturers to test appliances. If the appliances pass the tests, the testing agency will certify and "list" them. It's important to realize that every appliance is not required to be tested to every standard. Some standards only apply to certain appliance types. And some certifications are even completely voluntary. Marks of certification often provide a sense of confidence about a heater's performance. But, the lack of one doesn't guarantee inferiority.

Certification standards

That said, when a local AHJ tells you what's allowed, it'll also specify which heaters are allowed. So, we'll go over the ones you're most likely to run into while shopping for a heater.

Agencies

First are the organizations that come up with the standards. Often, standards agencies will collaborate on a standard. There are product standards and procedural standards. Procedural standards are often called "codes." Product standards differentiate categories of products and specify where they can be installed.

Then you have the testing and listing agencies. These are sometimes called labs. They provide manufacturer-independent testing and verification. When you look at the rating tag, data plate, or installation manual of an appliance, the big seal you see is the mark of the listing agency. This product documentation specifies which code or standard the appliance met.

In some cases, the agency that created the standard is also a testing and listing agency, but not always. Here's a list of the agencies that might have had a hand in determining standards for your future infrared heater:

• NFPA: The National Fire Protection Agency outlines procedural standards to prevent fire hazards.
• ANSI: The American National Standards Institute issues product standards for the commercial sector.
• AHRI: The American Heating and Refrigeration Institute creates guidelines for the heating and cooling industry.
• UL: Underwriters Laboratory issues product standards. The standards apply to a variety of products across many industry segments. It used to be catered to the needs of insurance underwriters needing a way to assess the risks of insuring work and exposition sites. Underwriter's laboratory is also a testing and listing agency.
• CSA Group: The former Canadian Standards Association, this is the primary standards agency in Canada. It's neat because it provides coverage of all the areas NFPA, ANSI, and UL do, but under one umbrella.
• International Electrotechnical Commission: Headquartered in London, the IEC sets international standards. These standards apply to almost all electric appliances. Some examples include power generators, transmission and distribution equipment, home and office equipment, and even batteries.
• Intertek: Intertek is a testing and listing agency. While they don't make standards, they test products for conformance to the standards. The certification mark you're most likely to see for infrared heaters is their ETL mark.

Standards testing

Standards

Some of the actual standards you may run into are below. Local code offices specify product types or procedures using these numbers:

• AHRI 1330: This is a special voluntary standard for gas-fired infrared heaters. It's not a safety standard, but it is one that can help you compare one heater to another. We'll go into more detail about it later.
• NFPA 54 / ANSI Z223.1: This is one of the "joint" standards. Installation of any gas appliance in the U.S. should follow NFPA 54/ ANSI Z223.1. These procedures are often called the National Fuel Gas Codes.
• CSA B149.1: These are the Canadian equivalent of the U.S. National Fuel Gas Codes.
• ANSI / NFPA 70: Another of the joint standards, this forms the National Electrical Code. All electrical installations in the U.S. must follow ANSI / NFPA 70.
• CSA C22.1: This is the Canadian Electrical Code.
• NFPA30A 7.6.6: The National Fire Protection Agency limits the operating temperature of infrared heaters. That is, infrared heaters in motor fuel-dispensing facilities and repair garages must not exceed 750 degrees. It's worth checking with your local AHJ for any other local restrictions on heaters. This is especially true if you're planning to install one in commercial areas where automobile fuel may be present.
• NFPA 88: This National Fire Protection Agency sets out standards specific to installations in parking structures.
• NFPA 409: Installations in aircraft hangars should also comply with this NFPA standard.
• ANSI Z83 / CSA 2: The American National Standards Institute and the CSA Group have defined the following product standards which classify different types of heaters.
• ANSI Z83.20/CSA 2.34: Gas-Fired Low-Intensity Infrared Heaters
• ANSI Z83.19/CSA 2.35: Gas-Fired High-Intensity Infrared Heaters
• ANSI Z83.7/CSA 2.14: Gas-Fired Construction Heaters
• ANSI Z83.26/CSA 2.37: Gas-Fired Patio Heaters
• NFPA/ANSI Z21.11.2: This joint standard is used to regulate residential vent free gas heaters.
• IP: This rating is issued by the IEC and designates what kind of intrusion to its enclosure an electrical appliance protects against. IPX4 indicates an appliance is protected from splashing. IPX5 means it can provide protection from water jets. An IPX6 appliance can withstand stronger jets than those in the IPX5 test. These certifications may or may not appear on outdoor appliances otherwise tested or listed for outdoor use.

While this list isn't exhaustive, it should give you a good sense of what you'll run into with your local code office and product manuals.

Personnel Considerations

It's not guaranteed that a job will be over your head. But not every appliance is designed to be installed by the avid DIYer. Even when you're planning to perform an installation yourself, it's a great idea to know where to get help should you need it. You should also get clear on the extent of service a provider is able to offer.

Hiring a professional

For design help, many manufacturers and some retailers offer their services. They can help you answer questions about what size heaters you need and where to place them. They may also be able to give you some general technical guidance during installation in a jam. But keep in mind that an over the phone consultant can't take the place of an in-person installer.

Depending on the scope of your project, you may need the services of one or more other types of service professionals. For jobs involving new construction or remodeling, you'll definitely have a general contractor. The more familiar your contractor is with your appliance, the better they can coordinate installation. You'll also want someone knowledgeable about your local jurisdiction's residential or commercial codes.

In a similar vein, you'll want an electrician you hire to be familiar with NFPA 70 and any gas plumber or fitter to be familiar with NFPA ANSI Z223.1.

One last thing to be aware of is that installation may need more than mounting and utility connections. It can be a huge help to have someone experienced with your appliance type on-site to make adjustments or test or fine-tune. While electric appliances tend to be more set and forget, gas appliances sometimes require some TLC.

When looking for professionals, you can start with neighborhood recommendation sites. You may also want to have a look at Thumbtack, Houzz, and HomeAdvisor.

Professional certification agencies can also be a great place to look for competent help.

Infrared heaters are popular additions purchased by homeowners who already have hearth appliances. So, you may have luck finding infrared capable technicians at the National Fireplace Institute (NFI). For gas-fired heaters, look specifically for NFI Gas Specialists or Master Hearth Professionals in your area. NFI trained technicians are especially sensitive to the need to treat each appliance as unique. They will also go beyond just the utility connection to complete the installation. While we can't be there in person, the technicians at eFireplaceStore carry and maintain NFI certified standing.

The American Society of Heating Refrigeration and Air-conditioning Engineers also maintains a listing of certified engineers in your area. AHSRAE professionals have unique in-depth knowledge about the intricacies of comfort heating. In fact, ASHRAE is also a procedural standards agency.

Some electrical appliances indicate they should only be installed by licensed professionals. Check your state's licensing requirements for electricians. Licensed electricians will know the local code requirements for your area, and they'll be able to tell you if your job will need a permit. Licensed electricians also carry the required insurance. They can be indispensable for making sure the wiring in your site or home is adequate for the spread of appliances you plan to install.

Leading Manufacturers

As we mentioned above, there's no shortage of manufacturer interest in infrared heating technology. Knowing some of the more well-known brands and industry leaders can be a big help navigating the sea of options. Our list below is not nearly exhaustive and doesn't mean to be a ranking. But it is a great tool to get you familiar with where to start looking for a solution that works for you.

Shipping packages with drones

• Infratech - Based in California and established in 2000, Infratech specializes in up-market outdoor personal comfort wall- and ceiling-mounted heaters for residential and commercial spaces. Their products are known for enabling modern designers to allow their imaginations to take flight. Infratech's quartz tube, medium-wave, lamp-style heaters can be seen in award-winning architect-designed homes, restaurants like Lemonade at Fashion Island, and Del Frisco's Grille, Wynn Casino & Hotel, the Minnesota Twins stadium, and BC Place arena.

• Bromic - Bromic is also based in California and is a direct competitor to Infratech that leans a bit more commercially. They even have a line of heaters designed specifically for luxury cruise ships and super-yachts. They offer both gas-powered ceramic plaque and electric quartz tube lamp-style heaters. You may have seen them in the MGM Grand Las Vegas, W and Sheraton Hotels and Resorts, and restaurants in international destinations like Sydney, Madrid, London, Los Angeles, Newport Beach, and New York.

• Ducoterra - Energy-conscious, sustainable, residential, and commercial heating has been Ducoterra's focus since 2011. This WA based company is unique in that it publishes quantitative studies and energy savings analyses about their infrared technology similar to those usually only performed by and for firms in the industrial sector. Their far-infrared radiant panels are favorites not only in private residences but also in children's therapy facilities and residential facilities.

• eTherma - Since 1981 eTherma has cultivated its image as a source of natural sun-like heat delivered to homes in style and elegance. Their forward-thinking product offerings include residential electric radiant panels, industrial and commercial overhead indoor and outdoor lamps, frost protection equipment for gutters, satellites, pipes, and roofs, as well as low-temperature floor heating systems. With several international offices, including one in IL, their products are used in the Prater Big Wheel Ferris wheel in Vienna, offices, and apartments throughout London, yoga studios in Australia, and Hohensalzburg Castle in Austria.

• Roberts Gordon - On the east coast in NY, Roberts Gordon has been producing heating solutions since 1960. In addition to residential gas-powered tube heaters for garages, they also make tube heaters for commercial, industrial, institutional, agricultural, and military applications. Museums, poultry barns, indoor tennis courts, and racing tracks, and gymnasiums all use Roberts Gordon heaters. They have been one of the most avid adopters of the new AHRI 1330 standard for radiant efficiency. Their innovative reflector design is capable of delivering some of the highest IR Factor of any low-intensity heater on the market.

• King - If it's electric and has to do with heating, King is probably into it, especially when it comes to heating controls. This WA based manufacturer has been producing a vast array of forced air convective, hydronic convective, and radiant appliances since 1958. Their infrared heater offerings include electric overhead quartz tube lamps for commercial use and metal sheath ceiling cove heaters for residential living areas.

• Detroit Radiant Products Company - Staying at the forefront of developing the field of infrared heating technology and education, Detroit Radiant was the first to develop its own listing agency (CSA) approved testing laboratory and continues to publish some of the most comprehensive information about infrared heating engineering and design. While their offerings mostly serve commercial and industrial needs, they also produce gas-powered ceramic plaque heaters and electric quartz and carbon fiber lamps for residential use.

• Herschel Infrared Heaters - This company is named after William Frederick Herschel, who discovered infrared radiation in 1800. Their mission is to change the way people heat themselves in their spaces. Based in the United Kingdom, Herschel offers electrically powered solutions for residential, commercial, and industrial spaces. They are the proud sponsors of heating the Herschel Museum of Astronomy and have a lineup that includes overhead lamps and workshop heaters, as well as radiant panels and ceramic emitter heaters.

Types of Heaters

Infrared heat gets harnessed in such a myriad of ways that it's easy to get disoriented when you start searching for the right heater. We think it's worth a moment to briefly outline all the kinds of infrared heaters you might see just to help keep you on track.

Infratech heating element

An infrared heater will fall into one of three categories based on its use: personal comfort, production process, and therapeutic.

Heaters for personal comfort can be used in central heating, zone heating, or spot heating strategies. Homes and businesses might place them indoors or out. But, they're more widespread indoors in industrial applications, like when they're used in airplane hangars and fire stations.

You might also see infrared heaters for commercial, agricultural, or industrial processes. They're used to produce and heat food. Some are made to keep animals warm in pens or stables. Among the more industrial versions are those used for curing, heat treating, moisture removal, non-contact drying, paint baking, and plastics forming.

Infrared heaters for sealing car paint

They have a role in healing and relief, too. Some models feature heat therapy, like those in saunas or IR (infrared) cabins. Others are designed for light therapy. There are even special sorts to help pain relief and to speed injury recovery.

How does an infrared heater work?

Infrared heating doesn't work the same way as other heating methods. So, before we plunge right into infrared heaters and how they work, we'll look at the important parts of infrared heater construction. Last, we'll look at how to evaluate how well the infrared heaters perform.

Comfort Heating Basics

If you're most interested in personal comfort, let's start with the basics of comfort heating. Two of the ideas sound the same: heating strategies and heat transfer processes. They're both important. But, even though they're related, they are different. The third idea we'll cover in heating is thermal comfort, which is what allows us to tie everything together later.

Heating Strategies

A heating strategy refers to the relationship between where appliances are placed, how they're controlled, and what spaces they heat. It's something people plan and execute. The three basic strategies are spot heating, zone heating, and central heating. It's possible a person might be using just one or some combination of the three in the same space or building. In fact, infrared can be used as part of any of the strategies as well.

When spot heating, you only generate heat for the desired section of a room, like a workstation. You'll typically only turn it on when you need it. This is the kind of heating you'd use a space heater for.

A zone might be a single room, a small group of adjacent rooms, or a group of similarly used rooms. Zone heating involves delivering heat to zones as needed or as requested. For instance, kitchens and bathrooms, or laundry rooms and basements, aren't occupied as much as other living spaces. So, they might be grouped as a "zone" and put on a separate thermostat than the rest of a home. This means that zones can be controlled independently of one another.

Infrared halogen heaters on an umbrella

Central heating is probably the most common in the U.S. In this strategy, heat is generated by the main appliance in a central location and then distributed to the different rooms or areas of a building. The single heat setting at the main appliance usually applies to all delivery areas. But, some sophisticated central systems may provide a level of zone control.

Heat Transfer Processes

A heat transfer process is how heat gets from one object to another. Rather than something people plan or do, it's the naturally occurring physics process that people work with or leverage. There are four ways heat can be transferred: conduction, convection, radiation, and evaporation.

An infrared heater in an auto shop

Conduction is what happens when you burn yourself on a hot stove. It's the transfer of heat between objects directly touching one another.

Convection is actually a compound thing. It's what happens when conduction and fluid motion get together. When one hot object warms the air (or other fluid) around it, which in turn warms another object it's touching, you have convection. This is how most conventional heating appliances work. Most people are familiar with forced air furnaces and everyday space heaters. But even "radiators," whether oil, steam, or hydronic, are really "convectors." They primarily heat the air around them to heat a room. The fins allow their hot surfaces to be in contact with more air.

Radiation is how heat transfers from one object to another when they aren't touching and when there's nothing between them. Waves of electromagnetic energy radiated from a warmer object to a cooler one right through empty space. This is the heat transfer process infrared heaters take advantage of. This is also why you might hear the terms radiant heater or radiant heating in relation to infrared heaters.

Radiation is how the sun is able to transmit heat to us through outer space. Taking advantage of it here on Earth may sound space-age, and it may be gaining popularity, but it's not new. It's how campfires and warmed rocks kept our ancestors warm. And, if you've ever used a fire back in your fireplace, you were exploiting radiant heat transfer. The ancient Romans kept whole buildings warm with radiant heating using structures called hypocausts. And before them, the Koreans were doing the same with systems known as ondol.

Example of direct infrared heat

When we use radiant energy for heating, the air isn't greedily the first in line to grab its share. We'll see why later. But for now, what's important is that radiant energy directly heats objects, like people, clothes, walls, and furniture. Once those things are warm, the air will follow due to conduction and convection. If, when it's cold outside, you've ever experienced the greenhouse effect in a room with a large bare window and the heat turned off, you've felt how this works. Radiative heating frees us from depending on warming air. That power is exactly why your face can feel warm on a sunny winter day and how infrared heaters keep people warm in open outdoor areas.

Evaporation is another compound process like convection. It's properly called state change and includes not only evaporation but condensation as well. But since it's a bit involved and plays more of a role in cooling systems than heating, we can skip it here. In short, though, it's the process your body uses to keep you cool by sweating. It's also why you may have heard of Low Heating Value and High Heating Value in reference to solid fuel-burning appliances.

Now, all three heating processes, conduction, convection, and radiation, are always at work in any room or appliance. As you've seen, they can't really happen in isolation from each other. For that reason, appliances are classed by which is the predominant heat transfer method they rely on. For example, for a heating panel to be considered a radiant panel by ASHRAE, more than 50% of its heat energy must be transferred into the room by radiation. Otherwise, it gets classified as a convective appliance.

At this point, we just need one more piece to finish our puzzle of comfort heating.

Thermal Comfort

Even though we tend to equate how we feel in a place with its ambient air temperature, experience tells us comfort is much more complex than that. Think back to our pleasant beach. 80 ℉ there sure feels different than it does in the desert. And that same 80 degrees definitely feels better in the shade than it does out of it. The weather report tries to help us compensate by giving us heat indexes and wind chill factors. But none of that tells us why we feel colder sitting on a wrought iron bench in winter than we do on a wooden one.

Portable infrared heater

This is where the concept of thermal comfort comes from and why we'll need it later to understand infrared heaters. Remember, they don't heat air!

For now, though, it's enough to know that thermal comfort is just as complex as it seems. To get a feel for how involved it is we can browse the definition ANSI and ASHRAE layout in Standard 55 (Thermal Environmental Conditions for Human Occupancy). It lists the following factors, only some of which can be measured in a practical way:

• Humidity
• Mean radiant temperature (the average surface temperature of the objects in a room)
• Dry bulb temperature (the ambient air temperature we're used to)
• Wet-bulb temperature
• Metabolic rate
• Clothing
• Radiant temperature asymmetry (as when you have a hot face but a cold back)
• Vertical stratification and gradients (as when hot air rises to leave your head warm but your feet cold)
• Floor temperature
• Drafts

Studies identify other factors, too, like a person's health and a thing called acclimatization. This is the big word that explains why 72 ℉ indoors might feel delightful when you come from outdoors in winter but not so much in summer.

There are also some generally accepted well-known causes of thermal discomfort. Too high a dry bulb temperature with too low a mean radiant temperature is a common one. Relative humidity below 50% is another, as is a dew point that's too low or too high. Warm air moving around is one most of us are familiar with.

In the end, the point of thermal comfort is that being comfortably warm is about more than just air temperature. And, though it's not as immediately obvious, it confirms for us something we already know in our gut. Namely, what's most important in comfort heating is what's happening in the lowest 6-8 feet of the room. That's where thermal comfort happens because that's where we are.

Infrared Basics

With the heating part behind us, we can turn to the infrared part. After we cover infrared energy in general, we'll need to look at how it behaves. Specifically, we'll look at how it's absorbed, how it's emitted, how it's reflected, and a thing called view factor.

Infrared Radiation

When we mentioned waves of electromagnetic energy transferring heat in the previous section, we were actually referring to infrared waves. As one section of the electromagnetic spectrum, it's the same kind of "thing" as visible light. Visible light is not itself color, but color "happens" when it hits an object. Infrared is the same way. It's not itself "heat," but heat happens when objects absorb it. In fact, we section off all the parts of the electromagnetic spectrum by their effects this way.

Below is a list of other sections of the electromagnetic spectrum and what they do. They're listed in order from shortest to longest wavelength:

Infrared heating technology

• Gamma rays: This is the dangerous "radioactive" radiation from nuclear explosions.
• X-rays: These are exactly what you think they are.
• Ultraviolet: These cause tanning, wrinkles, skin cancer, and eye damage. But they also make things glow (black lights).
• Visible light: Remember Roy G. Biv? (From shortest to longest this would be violet, indigo, blue, green, yellow, orange, red)
• Microwaves: These can also transfer heat but are used for cooking.
• Radio: These, too, are what you think they are. But besides TV and radio signals, they're also behind RADAR (Radio Detection and Ranging).

Infrared falls right between visible light and microwaves on this list. It would be just below red on the way to microwaves, which is why it's called infrared. Even though infrared is the primary energy behind heat transfer by radiation, it isn't harmful in normal circumstances. The one to be concerned about is called "ionizing" radiation, which is the UV through gamma wavelengths.

Except in special circumstances, infrared isn't visible. UV isn't typically visible either. But you've probably heard ultraviolet called UV light. That's partly because it's a close neighbor to visible light. For the same reason, you may come across the term infrared light. Like visible light infrared travels at the speed of light (186,282 miles per second), which for comfort heating applications is instant. And, while we can't normally see with it, all objects, including people, emit some infrared. This is what makes thermal imaging ("Predator-vision," if you remember the movie) possible.

Just as the overall electromagnetic spectrum is broken down into sections, or "bands," by its effects, the infrared band is, too. The nearest neighbor to visible light is called, unsurprisingly, near-infrared. It's also called NIR, short wave infrared or short wave IR and IR-A. Of all the infrared bands, it tends to penetrate the most deeply into human skin and some other materials. This makes it particularly useful in light therapy and in industrial paint curing.

The mid-infrared band (MIR) is also referred to as medium wave infrared and IR-B. For reasons we'll see later, this is a favorite band when a balance between heater distance and comfort is needed.

If you guessed the last band is called far-infrared because it's the farthest from the red light, you're right. It's also called FIR, long-wave infrared, and IR-C. Human skin and water really soak up this band. It's the most comfortable and gentlest-feeling of the three.

Absorptivity, Emissivity, Reflectivity, & View Factor

Absorptivity

Absorptivity denotes a material's ability to absorb electromagnetic energy. Every material absorbs some part of the spectrum better than others. For example, we now know that water readily absorbs long-wave infrared. (It also absorbs microwaves very well, which is why microwave cooking is possible.) On the other hand, infrared isn't really absorbed at all by gases whose molecules don't have at least three atoms each.

Since air is mostly nitrogen gas and oxygen gas, which each has only two atoms per molecule, it doesn't really absorb infrared at all. The only exception is the tiny portion of it that is water and carbon dioxide (less than 1%), both of which have three atoms per molecule. This diagram shows what the infrared absorptivity of human skin looks like.

Infrared heating diagram

Emissivity

Recall that all things emit some infrared. The term used to describe how well a thing emits infrared, or any other radiation for that matter, is emissivity. Just like with absorptivity, which wavelengths and how much of them a substance emits depend on the substance. In general, absorptivity and emissivity are flip sides of a coin. Better absorptivity usually means better emissivity. And if we want to know which bands or wavelengths a material is likely to emit, we can just look at which ones it absorbs.

Another interesting aspect of emissivity is that it increases with a material's temperature. So, the hotter a thing gets the more radiant power it will emit. But that's not all. As a material's temperature rises, the band of radiant energy it emits the most also shifts towards the shorter wavelengths. Remember the list of wavelengths from the previous section. Red wavelengths are closer to the long end of the spectrum, while blue is closer to the short end.

This is why as things get hotter and hotter; they first glow red, then yellow, then blue. Eventually, of course, they end up white, which is what happens when you have all the colors mixed together. Something that hot is probably emitting quite a bit of ultraviolet, which also explains why you don't want to look directly at it.

Putting absorptivity and emissivity together tells us two useful things about infrared heaters. First, the more closely the emitted infrared bands are to the ones the target material absorbs most readily, the better the results we get. Second, to get material to emit shorter bands, we may have to heat it up more, which may cause a brighter glow. The hottest infrared comfort heaters may put out a moderately bright orange glow. For any setting, a heater producer walks a tightrope to balance power output, a ratio of most useful bands, device temperature, and brightness.

Reflectivity

A substance might also reflect electromagnetic energy. Reflectivity is much like the other two properties we've discussed. Most materials reflect some part of the electromagnetic spectrum and reflect others. Some bands are fully reflected; others, only partially. As you might assume, a thing's absorptivity is lower the higher its reflectivity is. Shiny metals and mirror-like surfaces reflect the most infrared.

View Factor

Energy radiates from a source in straight lines perpendicular to the source's surface. Those straight lines form a pattern determined by the shape of the source, just like the visible light from a flashlight, light bulb, or a lamp. This becomes important for two reasons. First, energy only transfers from a source to another object where that object is illuminated by that pattern's shape. Second, the intensity of the power the object receives from a source decreases the further the object is from the source. That pattern, both its shape and the distribution of energy in that shape, determine a source's view factor.

Infrared Heaters

Now that we've covered the basics of infrared and comfort heating, we look at how all this comes together in actual appliances. We'll start with the basic components of infrared heaters and then take a look at how we can evaluate their performance.

Bromic infrared heating element

Infrared Heater Parts

The common parts of infrared heaters mirror the concepts we discussed in the previous section. That is, every infrared heater is composed of an emitter, a heat source, and a reflector working together to produce a desirable view factor of a preferred absorption range.

Emitters

As its name suggests, the emitter is the part of the heater that emits the infrared. Two major factors influence the choice of an emitter's material. One is the material's emissivity of the desired infrared band at the appliance's operating temperature. Remember, a heater is most effective when its emission spectrum closely matches the absorption spectrum of its target. The other is the overall radiant power output. A hotter emitter gives off more overall radiant power, which is important because power decreases with distance.

An emitter must be heated by a heating element, which may be a separate part or somewhat integrated. Because the emitter absorbs heat from its source and then re-radiates that energy as infrared, it may be called a heat exchanger in some applications.

In general, hotter materials give off a higher percentage of their infrared in the shorter wavelengths, which are closer to visible light. This requires the hottest heating elements. The hottest ones create view factors with the most radiant power. This makes them great for projecting heat from a longer distance.

But it may also make them uncomfortable if they are placed too close to occupants. This is where heaters with this kind of emitter get the label "high-intensity." The hottest ones also produce the brightest glow, which may be undesirable in some settings. Unwanted light from an infrared heater is called glare.

There are some emitters, though, which produce little or no glare at all. They give off the longest infrared wavelengths and tend to operate at lower temperatures. Heaters with this type of emitter are the most comfortable to be near and may be labeled "low-intensity."

The most common-emitter styles are metal tubes, quartz tubes, quartz bulbs, plaques, flat panels, and metal sheaths.

Tubal heating element

Metal tubes are several inches in diameter and aren't heated high enough to produce a glow. They may be straight or u-shaped. And, in large custom systems, they may even be serpentine. Black painted stainless steel is a popular material for tube emitters.

Silica quartz glass shaped into a narrow tube-like fluorescent office light is also an effective emitter. The glass itself is clear but may feature coatings for improved performance. Some quartz tubes have a reflective coating, like gold, on one side to improve their view factors. Others have a coating to reduce unwanted glare from the filament inside. They may even be filled with a noble gas still further performance gains. Filling a tube with halogen, for instance, extends the life of a tungsten filament.

The same quartz glass can also be fashioned into a more traditional bulb shape. Quartz bulbs are typically filled with a noble gas as well.

A flat plate with small perforations to allow tiny gas flames to spread evenly over its surface is called a plaque. Plaques are generally either made of metal or ceramic. The ceramic ones tend to give off an orange glow when heated. When plaques are thin enough to be malleable, they may be called "mesh." These allow emitters to be provided in custom shapes.

An emitter may also be shaped as a solid flat panel. Ceramic, sheet steel, and glass are popular materials for this type. Panel emitters have the advantage of a wide uniform view factor. They also aren't heated hot enough to glow. This combination makes them popular choices for living spaces.

Metal might be shaped into a very small diameter tube, similar to a quartz tube, and used as an emitter. To keep them separate from their large metal tube cousins, these skinnier tubes are called metal sheaths.

There are even some methods of using the surfaces of a room – like the ceiling, the floor, and the walls – as emitters. But since these are systems integrated into a building rather than individual heaters, they're best covered in another article.

Heat Sources

An emitter must be heated to emit the desired infrared energy. The part of a heater that does this is the heat source.

An electrical resistance filament is used to heat quartz tubes, quartz bulbs, metal sheaths, and flat panels. Some heating element materials you may run into are tungsten, nichrome, FeCrAl alloy (also known as Kanthal), and carbon fiber. Factors that decide the use of one material over another include how quickly a filament heats up or cools down, the preferred band of infrared, the temperature, and the desired radiant power output.

Bromic ceiling-mounted heater

Filaments may also be snaked throughout and integrated into flat panels. While the filaments used in flat panels aren't heated hot enough to glow, those used in quart tubes and bulbs are. The brightness and color of the glow is a function of temperature. And while some models try to suppress unwanted glare, others may take advantage of the glow to use supplemental lighting.

A gas flame may also supply an emitter's heat. There are both natural gas and propane models of heaters. A flame is used to heat metal tubes, but not metal sheaths. Some larger systems use fans to distribute a vortex-shaped flame down the tube. When the flame is pushed down the tube, the system is called a positive pressure system. Those with the flame pulled down the tube are called negative pressure systems. A gas flame may also be spread over the face of a metal or ceramic plaque. In either case, the flame is provided by a gas valve and burner similar to those on other fireplaces and heating appliances.

Reflectors

Not all the infrared leaving an emitter starts off traveling in the desired direction. But errant infrared can be redirected into a preferred view factor by using one or more reflectors. They're made from materials that have high infrared reflectivity. So, any infrared they absorb is small or even negligible.

Aluminum with a highly polished surface is frequently used. But there can be other reasons a heater may employ a different metal. Some high-end productions even use gold or thin gold coatings to make or enhance reflectors. The best reflectors are carefully shaped to obtain the best view factors for a setting. They may also be used on the non-business side of a flat panel emitter to maximize the infrared emitted into the room rather than the surface it's suspended from.

Infrared Heater Performance

Now that we understand how these heaters work, the next thing we'll want to know is how to tell how well they work. In other words, we're looking for a way to understand heater performance. The bad news is there is no standardized way to compare heaters yet. This is the case whether we want to compare one infrared heater to another or whether we want to compare an infrared heater to a convection heater.

Heating area of infrared heater

Believe it or not, the U.S. infrared industry has been trying to come up with a standard for the last 30 years. But, it's proven difficult. Describing the way radiation works requires a lot of complex physics and calculus, which we've avoided here. As we'll see later, even though there is currently one standardized metric for infrared heaters, it can't be considered "universal." We aren't completely in the dark though.

The lack of a universal standard for comparison has not stopped manufacturers of infrared comfort heating appliances from promoting a plethora of numbers suggesting the superiority of their models. So, in this section, we'll look at where the metrics we do have come from and what we can do to understand infrared heater performance based on the available information.

Where The Numbers Come From

The numbers we have about infrared heater performance mostly come from two sources: independent manufacturer case studies and individual manufacturer laboratory research.

Many independent studies claim to demonstrate the energy efficiency superiority of infrared heaters over their convection counterparts. To be sure, there have been some ASHRAE and AHRI agency certified studies. But, most of the cost-saving numbers you're likely to see were generated as part of individual manufacturers' customer case studies. A study like this tracks what a customer paid for energy before and after installing that manufacturer's radiant system.

An installed radiant system is likely composed of several individual infrared appliances and was designed specifically for that customer's building. While these studies give us some idea about the relative performance of infrared heaters, they don't help us make direct comparisons.

The other place numbers come from is the laboratory tests manufacturers perform when trying to design heater systems. Most of these tests are done to design a heater with optimal performance parameters for a specific manufacturing process. But some are conducted by manufacturers of comfort heating and therapeutic appliances as well. These yield numbers most useful to engineers evaluating products from a single manufacturer's catalog. But they can help us in a roundabout way in our comparisons of products from different manufacturers.

Appliance Metrics

In order to navigate the sea of marketing numbers we're likely to encounter, let's start by clarifying what questions we actually want to be answered.

In general, we'd like to know the following:

• What the basic input and output units are
• How well the fuel we put into a heater gets converted to heat
• How much of that heat is usable
• How much of the usable heat makes it where it's desired
• How much of the delivered heat is from infrared
• How much of the delivered heat is the right infrared
• How well does that heat do its job once it arrives

Being clear about which performance parameter we're thinking about is important. As we'll see, a manufacturer may refer to any of these when advertising a unit's "efficiency." But, we have to be careful. It only makes sense to compare identical measures across appliances. Not only that, but some measures only have meaning for certain types of appliances but not others.

In some cases, there may even be both a "radiometric" (physics) term and a different heating industry term for the same number. Most importantly, though, no one metric neatly sums up any heater's overall performance.

BTUs and Watts

We've spent a lot of time talking about radiant "energy." But how do we measure it? We know we'll need it if we want to compare how much "energy" we pay to put into a heater and how much "energy" we get out of it. It turns out there are two ways to do this.

Electrical meter

If you lift a box from the floor to your waist, you expended some energy. You might even say you did some work. In fact, that's one of the ways we can talk about energy: "work." Work tells us how much energy we used to move a certain amount of mass a certain distance. When we're thinking about heating, we consider the amount of "work" it takes to move a certain volume of a substance (like water or air) a certain number of degrees up the scale. One BTU will move 1 cubic foot of water at sea level from 60 ℉ to 61 ℉.

Back to our box example, we'd say someone who couldn't lift that box faster or more time per hour is more "powerful" than someone who could keep pace. That's the other way to measure "energy": power. Power lets us compare how long it takes to do "work." A watt is enough "energy" to move 1 gram 1 meter in 1 second.

You'll typically see watts used to measure inputs and outputs for electrical appliances and BTUs used for gas-fired ones. It's important to remember to keep in mind what you're comparing if you're looking at appliances using different "energy" scales. The "BTU rating" you may have seen on appliances is actually a measure of BTUs per hour. That's handy because it allows us to make comparisons to watts. One watt is the same as 3.413 BTU/hr. Those both measure power. But, if you come across a kilowatt-hour (kWh), that's a measure of work and should be compared to a flat BTU.

Combustion Efficiency

Our second question is the one of combustion efficiency. It tells us how completely fuel is burned. Put another way, it tells us how much of the potential energy in a fuel is converted into heat. Gas-powered heaters may have a combustion efficiency anywhere from 60% to nearly 100%. Vent-free appliances tend to be around 100%. As we will see, this is just one of several numbers a manufacturer may advertise as an appliance's "efficiency."

Notice that this only tells us what is happening directly at the heat source. We'll inevitably lose some of the heat from the heat source to the appliance itself through conduction and to the environment through convection. It's usually a very small amount. But, at any rate, that lost heat isn't really usable. To take those losses into account, we'll need a slightly different measure.

Thermal Efficiency

When those losses are taken into account the resulting percentage is called the thermal efficiency. This measure attempts to account for whatever heat is left over after combustion inefficiencies and appliance heat loss and available to be applied to the target area. Of course, if the appliance cabinet's hot temperature also contributes to heating our desired area, it's not exactly "wasted heat."

Home energy efficiency

A unit's thermal efficiency, for this reason, maybe very close to the heating element's combustion efficiency. It doesn't make much sense to talk about the "combustion efficiency" of an electrical resistance heating element. In that setup, though, the first law of thermodynamics assures us it's safe to assume all the electric energy supplied to the heating element ends up as heat. This is where you may have heard that heating appliances with electrical resistance heating elements have (near) 100% thermal efficiency.

Pattern Efficiency

Considering how much of the heat makes it where it's desired is a little trickier. With a convection heater, we know that there will be some useful heat loss through the ducting and that a lot of the warmest air that is eventually supposed to heat us ends up at the top of the room. Figuring out an efficiency requires some advanced computer modeling.

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