The B-vent pipe uses room air for combustion, much like an open wood burning fireplace. However, this could be a source of cold air if a downdraft occurs. One of the benefits of a b-vent gas fireplace is that it often has better visible flames than a direct vent model. But, it is not nearly as heat efficient, adding only radiant heat to the room.
Vent-free models are almost perfectly efficient, but have limited BTU outputs. They are also banned in many states and cities. Their high efficiency means they create almost no byproduct during operation. And, it is safe to vent them into the home. Eliminating the need for an outside vent makes them incredibly versatile. But, the small amount of particulate vented into the room may bother people who are sensitive to air pollutants.
Direct vent fireplaces provide a happy medium. They offer higher efficiency than the b-vent models with absolutely no effect on indoor air quality. Unlike b-vent models that must vent vertically, you have more freedom with direct vent models. As stated, direct vent models can vent at a vertical or horizontal angle. Some manufacturers also offer a pressurized vent system. These systems allow the pipe to be vented downward for short runs. This is perfect for fireplaces centered above a basement. You can direct the vent down to the basement. From there, you can route the vents horizontally along the basement ceiling and out an exterior wall. The best part about it is that it doesn't disrupt the floor plan above.
The option of horizontal venting also means you can save a lot of floor space. You can run the vent pipes against an outside wall or build them into a bumped-out enclosure. The termination, or end of the venting pipe, does need some clearance from surrounding structures to allow for proper venting. But, the versatility of both rigid and flexible direct vent systems means you can find a solution for virtually any scenario.
What is the BTU Output of Direct Vent Gas Fireplaces?
Direct vent models generate as little as 5,000 BTUs, up to very large models that generate 60,000 BTUs or more. The smaller models work well for warmer climates or small rooms such as bathrooms, where too many BTUs would create stifling heat. For more about low heat options, you can read our guide on low-BTU fireplaces.
The BTU rating lists the heat output. But, the efficiency rating tells you how well the fireplace converts fuel into heat. After all, you don't want to waste money on lots of fuel for only a small amount of usable heat. Due to their design and use of ceramic glass and circulating fans, some direct vent models are rated with over 85% thermal efficiency, a very respectable rating! However, not all efficiency ratings are equal, so here's a quick guide to the common ratings you might see:
AFUE stands for Annual Fuel Utilization Efficiency. It measures how well your fireplace converts fuel into heat. For example, consider a vented propane fireplace that is given 10,000 BTUs of fuel. During the burn, some of those BTUs are lost up the chimney, so you may end up with only 8,600 BTUs converted to useful heat. This results in an AFUE unit of 86%, since out of the initial 10,000 BTUs of fuel, 86% was converted into heat in the firebox.
Now, just because the fuel produces 8,600 BTUs of heat doesn't mean that your room will receive all 8,600 BTUs of heat. That's where thermal efficiency ratings come in.
Thermal efficiency ratings start with the remaining BTU number after AFUE is calculated. In the case of our example, we'll take this figure of 8,600 to measure how much of that heat actually makes it into the room. After all, some of the heat is absorbed by the chassis of the fireplace or lost before it gets to the room. If out of 8,600 BTUs of available heat, we test and find that only 7,500 BTUs actually pass through the glass and into the room, then the thermal efficiency rating would be calculated at 87%.
It's easy to see how these ratings get confusing. So, it's important to know which is which and keep them straight when comparing fireplaces.
Good news! Direct vent fireplaces come in a huge array of style and size options, so you can pick the right look for your home.
If you're looking for the appearance of a wood-burning fire, you'll be drawn to traditional styles such as the Superior DRT2000 series. These units feature a square or slightly rectangular opening with a ceramic fiber or refractory cement log set and glowing embers. The construction of these units simulate the look of a real fire.
They usually range in size from 32 inches to 60 inches. They also have various accessories like door overlays, decorative fronts, and remote controls. Most of their interior liners mimic the look of brick or stone, although a few models offer a reflective porcelain liner.
Linear (Modern) Style
These models feature a low, wide viewing area, characterized by a "ribbon" burner with a shallow row of flames. The smallest linear units are usually around 36 inches wide. But, some manufacturers offer custom models that are 100 inches wide and more.
The striking designs lend themselves to contemporary or modern decor. These models tend to favor the use of fire glass, ceramic stones, fire art (metal matrices, coils, cannonballs, etc.), or glass pebbles. Some models do offer log sets but as an accent. The liners themselves are generally reflective and give off a modern vibe. You can find options with fluted or corrugated metal.
Specialty models offer a compromise between the modern and traditional aesthetic. Models like the Napoleon GD19 and the
Empire Loft DVL33 are very popular for small houses or condos with limited floor space.
The Napoleon GD19 is a narrow width fireplace. Its design allows it to be elevated in the wall in smaller rooms. The Empire Loft DVL33 has a modern style with the shape of a traditional model. This makes it more suitable for installation in a smaller space.
Direct vent fireplaces offer two different ignition systems. These include the millivolt ignition and intermittent pilot ignition.
Millivolt Ignition System
By far the most common, this ignition consists of a standing pilot light and a gas valve. Very basic models may only offer manual control at the fireplace. But, the vast majority include a switch block as part of the valve. The switch block accommodates an on/off toggle-style light switch or a handheld remote control to operate the fireplace. The standing pilot generates electricity for the fireplace valve. This means outside power or batteries are not required for operation. So, these are excellent choices for people who live in remote areas.
Intermittent Pilot Ignition (IPI)
This fuel-saving ignition system uses a spark ignitor, an electronic valve, and a control module. The control module sends an electrical signal to the spark ignitor only when the unit is turned on, sparking and lighting the pilot. When the system is turned off, the burner and the pilot assembly shut down. This saves gas by not keeping a pilot light burning at all times.
Many of these models come with the remote control included. These systems require power to operate the electronics. So, we recommend supplying a 120-volt power supply when framing in this unit for installation. Most systems offer a battery backup as well. But, it's always better to supply line power rather than rely on batteries for normal operation. Ideally, you would use the battery system only during power outages.
Smartphone Integrated Control
The newest trend in direct vent fireplaces lets you control your fireplace from your smartphone. You can do this via Bluetooth connectivity. An app, developed by a 3rd party, controls a module in the fireplace. The app allows you to turn the unit on and off, raise and lower flame height, and control circulating fans. You can even control interior lighting or program these features on a set schedule.
If your direct vent fireplace does not come with Bluetooth capabilities, there's no need to worry. Manufacturers such as Flametec offer the i-flame series of devices as an add-on. These add-ons offer smartphone control on various models millivolt and IPI models.
How To Install A Direct Vent Gas Fireplace
Installing a direct vent gas fireplace can be a tedious task. But, each installation follows specific guidelines. Always start by framing the opening to the manufacturer-specified framing dimensions and to the required size and design of the enclosure. Next, have an electrician route the appropriate electrical feed from an adjacent circuit and a plumber run a gas line.
From here, you'll need to position, level, and anchor the fireplace into the framing so that it's secure. Make sure to cut out an access point to install your venting system, always following the manufacturer guidelines to maintain proper clearances from combustibles. After venting is completed, you always want to test run the unit to ensure proper operation. This will allow you to make adjustments as needed to obtain the proper flame pattern.
Once you're satisfied with the operation of the unit, you should work on finishing the enclosure with the finishes of your preferences. For more detailed DIY installation instructions, please read our Ultimate DIY Guide. If you're hiring a contractor to complete your fireplace installation, make sure to print off our Free Fireplace Installation Checklists for every stage of the installation process to ensure your contractor gets the job done right.
How To Clean A Direct Vent Gas Fireplace
Low maintenance is one of the major selling features for direct vent fireplaces. Like all gas fireplaces, the flue gases do not create as much build up in the venting system as a wood fireplace. So, the only venting maintenance required is an occasional inspection of the termination.
For horizontal venting, check for built-up yard debris, such as leaves and grass. Make sure that foliage is cut back to maintain adequate clearances. You'll also want to ensure the termination has not been damaged by objects such as falling limbs or an errant soccer ball.
Vertical terminations should also be inspected each year. Check for bird nests and wind-damaged components. Verify that any flashings and storm collars are properly sealed and still in place. Most terminations have a mesh screen to prevent unwanted access by birds or other animals. But, you should check to make sure the mesh is still present and intact.
Clean the glass as needed (usually 1-3 times per season) , depending on the humidity levels and the frequency of use. To do this, remove the glass and wipe it down with a water based cleaner and a cotton cloth. This is a convenient time to check that the logs and embers are still in good condition and are in the right place. Embers break down over time and will need to be replaced once they no longer glow as designed.
Lastly, inspect the valve compartment of the unit and vacuum away any spider webs, dust, or pet dander that may have accumulated in this area. Be sure to move slowly and do not disrupt any wires or modules as you work.
Because of the bulk and potential for damage to these fireplaces, almost every model will ship via freight carrier. To prevent damage, shipping companies place the units in crates, strapped and heavily wrapped. Inspect the shipment when it arrives, though. You want to make sure nothing was damaged or lost during transit. It's important to do this inspection before you sign off on the freight bill. The freight company is no longer liable for the shipment after you sign.
Summing It Up
Direct vent fireplaces are a great option if you are looking for a low maintenance gas fireplace that can be installed almost anywhere. Although you might not have the nice big flames of a b-vent fireplace, the efficiency, flexibility, and wide range of style options make it well worth it.
Commencing on January 1, 2015, new legislation went into effect that requires all glass fronted hearth appliances that exceed a 172 degree glass surface temperature to have a safety barrier screen as a standard feature. Many manufacturers redesigned their appliances ahead of this date to include a barrier screen as standard, while others made the screen a required add on. To stay in compliance while still giving our customers a choice, we do not require the purchase of a separate barrier screen in cases where the manufacturer does not make it a standard feature. However, the screen will always be presented as a purchase option and is highly recommended. An example of a unit with the screen listed as a configuration option is the Empire Tahoe Deluxe. As you will see, the screen is listed under the first configuration step for this unit. It is important to note that almost all hearth appliances allow removal of the screen after purchase, if the customer so desires.
Why is my direct vent fireplace not warming the area? The heat seems to be contained within the glass but not coming into the room.
The best way to move the heat away from the fireplace is to use the blower on your fireplace. If your fireplace did not come with a blower, please contact us at 1-800-203-1642 and we can assist you in finding the correct blower for your fireplace.
How far away does the vent need to be from a window?
The clearance from a direct vent termination to a window varies from model to model, so we would advise that you check with the specific unit's clearance requirements. This clearance is usually at least 12 inches, but it could be a few inches more or less depending on the model and whether it is a fixed window.
Submitted by:Tyler M. - NFI Master Hearth Professional on September 21, 2020
How can I stop the hot humid air from coming down the vent?
Be sure the humid air is only coming through the vent since direct vent gas fireplaces are sealed combustion systems. If the humid air is felt in the home, there are likely gaps in the chase construction, etc., that need to be sealed.
How difficult is it to switch a wood burning to a direct vent?
If you have a masonry woodburning fireplace, you can install a direct vent insert inside the fireplace opening and use a vent kit (usually consisting of two 3" liners) to run up through the existing (and functional) chimney. If you have a manufactured woodburning fireplace that is too small for an insert, you would need to remove the unit and replace the chimney pipe. So, the degree of difficulty varies depending on your application.
Submitted by:Tyler M. - NFI Master Hearth Professional on May 8, 2020
How do I determine how many BTUs I should look for when buying a fireplace?
When looking for a gas-fired unit, be sure to look for the "BTU" rating. A BTU (British Thermal Unit) is a measure of heat energy, and as a general rule of thumb, 35,000 BTUs will provide sufficient heating for about 1,000 square feet. By no means is this an absolute measurement, as windows, doors, ceiling height, and other factors come into play, but it is a good starting point.
Should I turn off the pilot light each time I use the fireplace?
If your fireplace is electronic ignition, the pilot will automatically turn off when the main burner turns off. If you have a standing pilot, it's okay to leave the pilot on while fireplace is not in use.
My Martin 4500 vented gas propane fireplace wouldn't start up using the ignitor and I finally got it to light up with a torch. However, it doesn't have a high flame. What parts would I need to repair this?
Martin models have long since been discontinued and we do not offer any parts. We apologize for the inconvenience.
Submitted by:Tyler M. - NFI Master Hearth Professional on December 2, 2019
We have a new Cape (single story, unfinished walk up attic, with a 10/12 roof pitch). We would like to install a see through gas fireplace on the first floor that would have a floor to ceiling wall and we would be able to walk around either end of the fireplace (it will not be attached to an outside wall). I like the idea of a direct vent fireplace, but have a few questions.
1) What is the size of the vent required?
2) Does the vent need to run vertical, or can it have bends in it?
3) Can it be vented through an eave soffit or does it need to be vented through the roof?
4) If vented through the roof, what height does the top of the vent need to be?
5) Can installation be completed by a DIY-er, or should it be left to a professional?
1-Most units take either a 4"/7" or a 5"/8" vent pipe.
2-It can have bends in it to avoid rafters, studs and to get to an ideal locate for roof penetration as well. The amount of horizontal run does depend greatly on the unit and the amount of vertical it is run as well.
3- It can vent either way or vent on the horizontal on the side wall of the home. I can help you design the best venting option for the unit and your needs for you.
4- This varies on the unit as well. In general it can be between 12" and 24"
5- That really depends on the Home Owners skill set. A lot of the framing and finishing of the unit can be done by a DIYer with good wood working and hand tool skills. The gas connect though should be handled by a profession gas tech or plumber (again depending on the DIYers skill set)
Can I do a basement install with a direct vent LP gas log fireplace?
Yes, a direct vent fireplace can indeed be installed in a basement. If you are horizontally terminating the venting system, the horizontal termination cap will need to be at least 12" above grade (perhaps more per your local code or the manufacturer). We have snorkel termination caps available to help achieve this clearance, if needed for your application. Please let us know if there is a specific model that you have questions about and we can provide more specific information.
Submitted by:Tyler M. - NFI Certified Specialist on March 17, 2014