You can see how quickly this gets complex. On this front, though, many manufacturers are good about providing a diagram of a heater's view factor so you can position it or figure out how many you'll need to cover a space. Don't be surprised, though, if you come across an "efficiency number" for this. In fact, this is sometimes reduced to "watt density."
At this point, it makes sense to ask how much of the heat from an infrared heater is distributed as infrared. Remember that there's still some convection going on – any air that happens by that hot heat source will get warmed up, decreasing the amount of energy left to send out as infrared. Some heaters intentionally exploit this for room heating benefit while others try to minimize or eliminate it.
There do happen to be a couple of ways to measure what proportion of the heating action of a heater is radiant.
The ANSI and AHRI developed Standard 1330 in 2015. It assigns a rating to a heater based on how much of its heat is delivered by radiant energy. You may see one of two ratings: Infrared factor (IF) and radiant emission value (REV). IF is the older rating system, which was replaced because the testing equipment manufactured for measuring it turned out to be inconsistent. In some cases, there were differences of 10% between repeated test results for the same heater. REV is the newer method adopted in 2018 and is more accurate. You may see either one in practice.
Both ratings are based on similar testing procedures and calculations, however. A heater is placed in front of a radiometer, which is a sophisticated machine to measure radiant output. From the test results and quite a bit of calculation, a ratio of radiant energy that made it to the radiometer to the total energy input can be determined. New testing equipment was manufactured to ensure consistent results with the REV method.
IR Factors can range from 7 to 15, and REV's from 80 to 120. Both systems indicate a range of roughly 30% to 70% radiant heat transfer (as measured by a gross radiant coefficient), implying that the rest is transferred by conduction and convection. It's important to note that Standard 1330 testing is not mandatory; it's only voluntary. So, not every appliance will have this rating. In addition, 1330 is only applicable to gas-fired heaters whose energy can be radiated into a single measuring plane.
So, this won't help make comparisons between gas and electricity-powered units. Last, a higher REV doesn't always mean a "better" heater. This is because REV doesn't tell us how "hot" the heater is or how much of each band it puts out. It just tells us what percentage of the heat that ended up in the target got there by radiation. So, be sure to consider these aspects when you see manufacturers use this "efficiency."
Another way a manufacturer may advertise its heater's radiant efficiency is by giving the emissivity of the emitter or the heating element. Emissivity is actually a value, the ratio of how much radiant energy an actual body emits at a given temperature versus how much radiant energy it's theoretically possible for an ideal substance to emit at that temperature.
The theoretical ideal substance used as the comparison to determine the denominator of that ratio is called a black body. Think of emissivity as a unit-less number expressed as a decimal. A perfect black body would have an emissivity of 1. This is why you may also see emissivity expressed as a percent when used as an "efficiency" in marketing materials.
When you see manufacturers use this as their "efficiency," remember that it only tells us how well the emitter or heating element works to emit infrared. Keep in mind, too, that for full context, we can really only compare emissivity of one material to another at some specified temperature. Remember, an object's emissivity gets closer to 1 as it gets hotter. For example, a nichrome filament may have an emissivity of .90 when heated to 392 ℉. But that same filament would have a .97 emissivity when heated to 932 ℉. Just like REV, emissivity also doesn't say anything about the total energy in as compared to the total energy out.
The last performance area we want to understand is how an infrared heater affects us and our surroundings. More specifically, we want to know what we can measure to let us know it's working. If we were thinking of a convection appliance, this would be rather straightforward. We'd simply look at the thermostat temperature. We've habituated ourselves to associate our degrees of comfort with the degrees on that dial. But, since an infrared heater isn't heating the air, does the air temperature of the room still apply? The answer can be found in the elements of thermal comfort we discussed earlier. Let's go through them briefly and see what metrics are there.
The sneaky trick behind the magic of comfort heating surprises most people. The secret is that comfort heating work largely flows in a direction opposite to the one we tend to think it does.
As a result of our metabolism, our bodies constantly produce heat long as we're alive. And, we need to be able to lose some of it in order to stay comfortable. Otherwise, we overheat. But, if we lose heat too fast, we feel cold. So, much comfort heating becomes about slowing the rate at which our bodies lose heat so we don't feel cold.
Unless we're standing close enough to it to feel uncomfortable, a convection heater isn't increasing heat in our bodies at all. Its job is to keep our surroundings warm enough that we only lose heat at a comfortable rate.
There isn't a handy tool to measure metabolism in everyday life, and that's fine. It's not even a big deal to know that we crank out about 400 BTUs/hr when we're just sitting around. But, knowing that keeping warm is actually about managed controlled heat loss is critical for everything else to make sense.
Dry Bulb Temperature
This managed heat loss process works through both convection and radiation. We're used to the convection side of it even if it's not obvious at first. But, it becomes clear when we think about it. Although most of us feel comfortable in a room full of 70 ℉ air, our skin is 92 ℉. The air can't heat us up because heat transfer only works in the opposite direction, from warmer to cooler. So, our bodies lose their extra heat to the air through convection, even in "warm" rooms. We feel "warm" because we aren't losing too much heat to that air too fast.
The technical name for a device that measures air temperature is a dry bulb thermometer. So, this number, the one on our thermostats, is called the dry bulb temperature.
But we're already familiar with this one, so let's look at how this works on the radiant side of things.
Mean Radiant Temperature
Radiant temperature is the temperature of an object measured by the amount of infrared it emits. Rather than a dry bulb thermometer, the radiant temperature is measured by a pyrometer. You may have seen these devices labeled as "infrared thermometers" in the hardware store.
If you've ever leaned over a cold freezer with the lid open, you've experienced why the radiant temperatures of objects around you matter. You may have thought the chilling effect you felt was due to cold air rushing up from the freezer. But, cold air tends to sink under warmer air. So, while some cold air may have been swirled up towards you as you opened the freezer lid, that lingering cold feeling on your face was from something else. Remember how infrared will always radiate from a warmer body to a colder one? You felt cold because you were losing heat quickly through radiation to that freezer.
So just like with the freezer, we continually lose heat to cooler objects in our surroundings as well. Those objects include surfaces, like floors, walls, and ceilings, as well as furniture and other objects. This is one reason why well-designed indoor radiant systems often intentionally heat floors, walls, or both.
Mean radiant temperature (MRT) is the average of the radiant temperatures of all the objects in a room. And it can be measured with a device called a globe thermometer. Some manufacturers of infrared heaters even provide globe thermometers, too. This allows their customers to measure and manage "object" temperature the same way they would air temperatures with convective systems.
So, it turns out we have two "pumps" we can use to manage our controlled heat loss. This has two big consequences. First, we might expect that losing heat more rapidly through one method than the other would feel "strange." In fact, this is exactly the case. When air is warm but the surrounding surfaces aren't, we feel a chilly feeling akin to clamminess. Second, we might expect that if both "pumps" are working well, neither pump needs to be working quite as hard as it would on its own. This, too, turns out to be true. In a room with a decent mean radiant temperature, we feel as comfortable as we would in a room with a 3-5 ℉ higher dry-bulb temperature. This means we can set our dry bulb thermometer lower.
This relationship between dry bulb temperature and mean radiant temperature is so important that it gets its own word. The average between the two, weighted for convective and radiant transfer, is called the operative temperature. For most rough calculations, the weighting is omitted. This number is used fairly frequently in infrared comfort heater literature. It is also something ASHRAE uses in its guidelines for designing heating and cooling systems correctly.
In the same way that our bodies are continually losing heat to their environments, they're losing moisture, too. Our skin, nostrils, throat, eyes, and nasal passages all need moisture to function properly. Some water is always evaporating from those tissues, just like water evaporates from a glass left out to sit. And, just like with heat, when we lose moisture faster than we can replace it, it's uncomfortable. We dry out.
The amount of water in the air determines how much water can evaporate from our bodies' tissues. We call the amount of moisture some air is actually holding compared to how much it's possible for it to hold at that temperature its relative humidity. If you have an indoor digital thermometer with a humidity readout or a humidifier with a "hydrostat," then you're familiar with this percentage.
By allowing us to keep the air temperature 5 degrees lower, it improves the relative humidity of the air in a room. This means we don't have to add as much moisture to it to feel comfortable.
It's fairly easy to grasp that the less moisture is in the air, the more moisture we have the potential to lose. But if we really want to understand why we dry out, especially when it's cold, it helps to look at one more number.
When we start with the dry bulb temperature and the relative humidity of the air, we can derive how cold that air has to get in order for the moisture in the air to condense back into droplets. That temperature is called the dew point. You may have heard the local weather person talk about this even more than the humidity.
The beer you pull from the fridge "sweats" because it's colder than the dew point temperature of the room you're in. The lower the dew point of the environment is, the less condensation your beer will accumulate. On the other end of the scale, though, the lower the dew point is, the more evaporation is possible. That is, the lower the dew point, the drier the air feels. The bigger the difference in the temperature of the air around us and the dew point temperature, the faster we evaporate water and the more dried out we feel. Our bodies actually feel that rate. So, even when it has high relative humidity, like after a winter rain, cold air feels so dry because it has such a low dew point.
The cold outdoor air that comes into our homes through natural ventilation has that same low dew point. We can heat that air all we want to try to feel more comfortable. But until we add moisture to it, its dew point will remain the same, and we'll feel dry.
Dew point also tells us why cold exterior surfaces in a home can be subject to condensation even in winter. When we heat the air first, the walls and windows are the last to warm up. This means they risk staying at or below the dew point longer. In fact, in some buildings, some exterior walls or slab floors may never warm up without some help.
So, by first heating surfaces like walls to temperatures higher than the dew point, infrared heaters have the potential to reduce or eliminate that condensation issue. Less condensation means less mold, fungus, and bacteria.
Infrared Heater Styles
Infrared heaters come in a myriad of shapes and styles, even within the comfort heating niche. In fact, the types can look so different from one another that it's possible to have two side by side without knowing that both were infrared heaters. In this section, we'll see how to recognize the various styles and peek at where they're used and what each is best for.
The most straightforward way to divide up heaters is by their emitters. It's usually the most recognizable or prominent feature of a heater. To an extent, they even determine the shape of the main appliance cabinet. We covered emitter types already. So, you'll recall that the main emitter types are: quartz tubes, metal sheaths, metal or ceramic plaques, metal tubes, and flat panels.
Quartz Tube Heaters
All quartz tube heaters run on electricity, which heats the resistance filaments running through their emitters. You may see these long rectangular heaters referred to as "lamp" style heaters. That's apt because many of them look more or less like chubby fluorescent light fixtures with glowing orange heating elements. The reflector typically lines the inner surface of the main housing behind the emitter. In front of it, there's usually a wire cage to prevent inadvertent touching.
Bromic heater with a cylinder heating element
Makers are able to use quartz tubes for a wide range of applications. Different models of quartz tube heaters strive for different balances of IR-A and IR-B for projection from a distance or colder outdoor use, and IR-C for absorptivity. And their electric filaments reach their target temperatures in just seconds. These emitters are easily adapted into outdoor models, which feature weather-resistant stainless steel or powder-coated housings.
Outdoor Overhead Quartz Tube Heaters
Many heaters mounted in ceilings or coves or outdoor zones are quartz tube or lamp style heaters. Terraces, large pergolas, and an outdoor dining or entertaining areas all benefit because they occupy no floor space. The higher-intensity models can even be positioned further away from target areas. Since they can be placed about anywhere electricity can be supplied, you'll see models made for garages and even boats.
Quartz tube heaters have some of the highest operating temperatures of infrared heaters. So, the hottest high-intensity models may require higher mounting and larger clearances. It's also worth checking the approved uses of models of this style. Some commercial and industrial use units are not approved for residential use.
Outdoor Floor Stand Quartz Tube Heaters
Because the lamp style is so versatile, some manufacturers make versions of it for settings where mounting overhead is not an option, too. These models share many qualities with their ceiling-mounted kin. But since they're positioned closer to their targets, you won't find high-intensity lamps.
Pole-mounted portable infrared heater
This makes them better suited to outdoor "areas" than to larger zones. They must, of course, be placed in the cord's length to an electrical supply. And, they'll take up floor space. On the other hand, many are portable so they can be deployed and stored as needed. Even the more permanent ones are mounted atop a pole, which minimizes their floor footprint.
Indoor Overhead Quartz Tube Heaters
Quartz tube lamps can even be adapted for indoor use. While they look and work much like the outdoor models, the residential versions you're likely to only see are for garages. They're more commonly used to heat individual work areas, like workbenches, entryways, and exits in industrial buildings. You may have seen these heating stadiums and sports arenas.
They're also popular for heating large open buildings with high ceilings, like warehouses, aviation hangars, and fire stations. Some are even specifically designed for saunas, which is where you may have heard the term "IR cabin." As with the outdoor models, you'll want to check whether the approved use is commercial, industrial, or residential.
Wall-mounted infrared heater
Residential Indoor Space Heaters
Quartz tubes also find use in most designs for infrared personal space heaters. Even though all have the signature orange glow, their shapes and sizes are only limited by manufacturers' imaginations. You'll see them in cabinet styles, tower styles, and even "circulating fan" styles. The heating element and emitter are hot, though not as hot as those for outdoors or long distances. So, they do have a safety cage on the front. Despite that, these appliance's cabinets typically aren't hot to the touch.
A blower fan is a common feature among residential space heaters and they serve two purposes. While this type of heater still exploits infrared, their radiant output is less than other styles. Since a larger portion of their heating power is convective, the blower helps distribute the warm air. In addition, the blowing action helps to disperse heat from the cabinet. You may see this kind of heater advertised as "dual radiant and convective" or something similar.
These inexpensive heaters are popular for heating bedrooms and living spaces in homes.
They're typically portable; even the larger ones may have wheels. And it's easy for manufacturers to pack extra features into the cabinet models. For instance, music speakers are frequent bonuses. As great as they are though, it may be hard to take full advantage of infrared's benefits with them. When they sit on the floor, it can be tricky to get a view factor to adequately cover a target area.
Metal or Ceramic Plaque Heaters
Plaque heaters are always gas-fired and come four basic styles. They are almost always recognizable by a glowing orange "plate" that you can tell has little holes all over it when you look closely. That said, metal plaques won't always glow. But if the heater you're considering runs on gas and has a perforated emitter, there's a good chance it's one of these.
Overhead Plaque Heaters
If you've heard the term "box heater," this is the kind of appliance it refers to. Its arrangement of rectangular glowing orange plaques bordered by a large protruding reflector makes it look like an open shoebox. Since these are hung from a height, their emitters will try to balance IR-A for distance and IR-B for absorptivity. Their plaques are almost always ceramic.
Although they may need both gas and electricity supplied from overhead, these are a popular choice in large garages and open bay buildings. They can be aimed diagonally and may even be aimed within a range of angles.
Because they operate at such high temperatures, some models may not be used in residences. It's a good idea to check a model's manual for where it can and can't be used. Indoor swimming pools and outdoor areas are two locations that might be off-limits.
Mushroom Top and Cylinder Heaters
These might be the most familiar style of outdoor patio heater. Mushroom tops look a bit like floor lamps. But where there would be a light bulb at the top of a lamp, infrared heaters have a cylindrical metal plaque emitter. The mushroom's "cap" is actually a reflector to direct infrared down to people and to help trap a bubble of warm air. The emitter on some models runs the majority of their height, essentially replacing the stem.
Portable gas heater
A newer design even looks like a skinny pyramid with a clear glass tube at its center. Flame runs up the tube to the plaque emitter. But, in the process, the heated glass tube also acts as an emitter while adding a stunning display. The reflectors at the tops of these are usually small and rectangular.
One drawback to this heater style, however, is its limited range. Their emitters are smaller in comparison to those of other outdoor heater styles. On top of that, the emitters on floor stand models are above head height and aimed outward. Infrared must be reflected back down to the target rather than initially directed at it.
Floor stand mushroom top and cylinder heaters have provided residential and commercial area heating since 1961. Found in both portable and fixed models, they give potential users the option for either gas plumbing or propane tanks. Recently, some manufacturers have even shrunk this design down to tabletop size for home use. In any size, most of these heaters are not only familiar but attractive.
Tank Top Heaters
A tank top heater looks just like a box heater, except that the box attaches directly to the top of a propane tank. This makes it easy to move from place to place. It's easy to see why this style heater is a favorite for construction sites and other outdoor work areas. And the view factors and watt densities of their glowing ceramic plaques tend to be perfectly matched for the task.
As their name implies, these heaters are mounted between floor and head height on a wall in a home. They're a common alternative to blue flame heaters. Like them, some even have an available fan option. In front of the glowing ceramic plates is a metal cage to prevent users from touching one by mistake.
The more furniture impedes their view factors, the less infrared benefit makes it into a room. But, they are so convenient to install and have such short response time that they are a staple for zone heat in many parts of the country.
Metal Tube Heaters
"Tube brooders," as they're called, are always low-intensity heaters. They emit longer wave infrared, which is known to be the best for comfort heating. These are always mounted overhead. Just like a box heater, a metal tube heater has a reflector around its edge. Unlike a box heater, though, it doesn't glow. In their long history, they've picked up as many nicknames as there are places people have found to use them. Some of the others you may have heard are "push tube heater" and "stick heater."
It's worth considering that their overhead position does require gas and electricity to be available from above. And, while not a concern for most units, the temperature can decrease quite a bit down the length of the longest tubes. A low-intensity output heater will also have the most trouble overcoming high winds or outdoor cold.
But because they produce gentle comfortable heat, metal tube heaters see lots of use in the seating areas of retail centers and restaurants. For their insides, warehouses or plants may have them custom-designed to canvass an entire building. Or they may use standard models to only provide heat in zones where people work. Either way saves valuable floor space. This style is so trusted for industrial open bay-like areas, it's no wonder they've become popular for home garages, too.
Flat Panel Heaters
Of all the styles of an indoor heater, flat panel heaters may be the "coolest." They not only operate at the lowest temperatures, but they are also the most stylish. Thin and rectangular, they can be hung on walls or suspended from ceilings. There are some that fit into ceiling coves. They can have bars fashioned onto them when they're built as bathroom towel warmers. And, some are disguised as functioning mirrors. A handful of companies even offer custom prints on the fronts so they can double as wall art.
Infrared portable heater at a restaurant
These are favorites of infrared specialists heating living and office workspaces. Their profiles are slim, they run on electricity, and their response time is quick. So, they're easy to work into building-wide zone heating plans. While most panel heaters are of the low-intensity type, there are some medium intensity models, too. They may be preferred in high ceiling rooms used as recreational spaces. Hot yoga studios, for instance, are growing advocates.
Flat-panel heaters overcome most challenges using infrared in "normal" spaces. But since they can melt into a background unique care is due. They're still heating appliances. Even though only prolonged contact is likely to cause burns, their surfaces are still hot to the touch.
Infrared heaters for most uses are sized for parcel delivery. They're light enough to be delivered to your front door and don't usually require a signature.
As with any appliance, however, take into account the fact that yours has been on several loading docks and many freight trucks before getting to you. Be sure to consult your installation manual thoroughly. There will be checks and adjustments to go through to make sure your appliance works the way it should.
Even though it's only necessary in a small number of cases, be prepared for some cleaning in tight spaces or tweaking rather than a complete plug and play experience. This is especially true for gas-fired appliances and is why most manuals insist that installation and service be performed by knowledgeable professionals. There may be a little more to do than just making the utility connection.
You'll recall each unit is a unique combination of energy input, heating element, emitter material, and reflector design. This leads to different view factors and watt densities in the desired wavelengths. This also means there is no one-size-fits-all positioning or appliance sizing for all heaters or even to any heater types.
Outdoor patio area
But, in a general way, you can think about "aiming" an infrared heater the same way you would a flashlight or a light fixture. If you put a radiant heater low to the ground in a spot where its "light" is blocked by furniture, you won't get its full benefit. Anywhere there's no "light" will stay cold until heated by the convection or conduction from the rest of the room. This is why many models are designed to be placed at height and "shine" heat down on target areas for the broadest coverage, just like traditional lights.
In every case, it's best to consult the model-specific documentation. Remember that considering watt density alone may not be enough. 20,000 watts of high-intensity infrared need to be positioned differently than 20,000 low-intensity watts.
Single appliance installations in residential settings are ones most homeowners should feel comfortable tackling themselves. But, the situation is different if we're considering a multiple appliance installation as part of a well-designed zone heating plan. In this situation, you should take advantage of the manufacturer's in-house design service whenever possible. If you can find one, you'll also benefit from consulting with an installer who has previously worked with the brands or models you plan to install.
Fuel Access and Cost
It's tempting to let yourself get swept up in claims about energy savings. But the hard truth is that both the cost and availability of fuel gas and electricity vary by region. So, if you're planning on doing a cost comparison, be sure to check with your utility provider and check your desired product's installation manual for consumption information.
Outdoor natural gas line
Routing fuel gas or the right voltage of electricity to a planned appliance location may also be restricted by a building's layout. Consult with your gas plumber, electrician, or general contractor to make sure you don't run into any surprises.
Ventilation, Clearances, and Avoiding Burns
No matter what type of infrared heater you're thinking about, your choice of its final location will also need to take into account ventilation, clearances, and avoiding burns.
If you're considering an indoor gas-burning appliance, you'll need to plan for adequate ventilation. The goal is to make sure there's enough oxygen to maintain combustion without depriving humans of what they need for respiration. Ventilation also provides dilution and evacuation of combustion by-products.
Gas heaters classified as "unvented" don't require any special vent pipes to carry fresh air to the appliance or to carry exhaust to the outside. When operated properly they only produce the same "exhaust" gasses human beings do. Still, though, they require proper ventilation, and indoor units should not be installed in what are called "confined" spaces. Residential appliances need a minimum fresh air opening of one square inch for every 1000 BTU/hr of burner capacity for proper ventilation. Unvented appliances also don't operate well above 4000-4500 feet because the air already has less oxygen.
Portable infrared gas heaters
How far manufacturers specify an appliance must be from combustibles in each direction also affects its placement. Failing to follow these specifications puts you at risk of starting a fire. What often isn't given enough weight is that a fire may not result for months or years after the installation. Manufacturers will also spell out how to position their models so as to minimize the risk of burns. Even though many have safety features to prevent directly touching an open flame or high-temperature emitter, leaning against a hot housing or emitter panel could prove to be painful.
Some requirements may be a little different from model to model, so always be sure to check the documentation. Your installation planner or installer is a good resource to double-check with, too.
Care and Maintenance
Something to love about infrared heaters is that they don't have many parts to wear out. In fact, electric heaters without fans may only require occasional bulb changes and dusting.
As straightforward as they are, you'll still want to keep a couple of things in mind when tending to an electric infrared heater. First, make sure the appliance has been turned off. Also, it needs to be disconnected from its power source and cooled to room temperature before performing any maintenance. And, second, never handle quartz tubes or bulbs with your bare hands. The oil from your skin can cause hot spots on the tube surface, which may shatter when the appliance is turned back on and heats up to temperature.
Plumber fixing gas line blockage
While the maintenance of an electric heater can typically be performed by the homeowner alone, gas-fired heaters require a bit more attention. Their valve trains should be checked at least once a year. And it's a good idea to have a certified professional gas appliance technician do the heavy lifting. In this respect, they're just like any other gas-fired appliance in your home or business.
Gas supply hoses will need to be checked for wear. You'll want to compare the flame pattern on ceramic and metal plaque burners to the pattern in the installation manual to make sure its right. There shouldn't be any blue areas. Burners of any type should be cleaned with compressed air, particularly in their air intakes or shutters. Injectors, housings, and control compartments, too, benefit from being cleared of dust.
With all the information presented in this article, you're well on your way to earning a certification in infrared heaters! Just know that a well-built gas-fired infrared heater can reasonably last 15-25 years. Radiant panels, which are essentially a solid-state design, can even last 40 years. The only heater type with parts needing regular replacement is quartz tube heaters. While some have longer life spans, 5K hours is a good average tube life. For comparison, there are 8740 hours in a year. If you still need more clarity, our NFI certified technicians are more than happy to assist you.
Do ventless gas infrared heaters create moisture in a room that is noticeable on the windows?
Water vapor is a byproduct of complete combustion and all highly efficient appliances such as vent free infrared heaters will create some moisture in a room. Whether or not it is visible on windows and other glass surfaces would depend of a wide range of variables and we cannot say for sure.