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Ventless Gas Log BTU Calculator!

December 11, 2009
By: Greg Tillotson
Gas Log Expert & Webmaster for Hansen Wholesale

Recently, a visitor asked if there was a formula for determining how many BTUs a ventless gas log should put out depending on the size of a room. Now this is certainly not the first time we have been asked this question. So after answering this same question over and over, I decided to create the very first online BTU calculator for Ventless Gas Logs.

Ventless Gas Log BTU Calculator!

Ventless gas logs MUST NOT exceed a certain BTU rating based on the size of a room. The formula for calculating the maximum BTU allowed is: Room Width x Room Length x Ceiling Height x 20. You can use this tool below to perform the calculation. Find out why it is important to limit the BTU output of ventless gas logs based on the size of the room!

Enter your ROOM DIMENSIONS:
Width x Length x Height x =
????? BTUs Max
Important Note: Professional Installation is required for all ventless products. Vent Free gas logs are not recommended for use in elevations over 2,000 feet. We advise that you install a high quality Carbon Monoxide Detector if you install a ventless gas log. Some cities do not allow vent free gas logs to be installed in bedrooms, bathrooms or other confined spaces, others do not allow ventless gas logs to be installed at all (California for example). Check local building codes for any restrictions or conditions regarding ventless logs before you purchase or install them. You may also view this: USA Map of Ventless Code Status.

Why must you limit the BTUs a ventless gas log burns in a room?

I'll first use a quick scientific approach, then we'll put it in layman's terms:

The scientific formula that represents the combustion of Natural Gas in its pure form which is methane:

CH4[g] + 2 O2[g] -> CO2[g] + 2 H2O[l] + 891 kJ

This formula shows that every molecule of Methane gas consumes 2 molecules of oxygen when it burns and creates 1 molecule of carbon dioxide and 2 molecules of water... while generating 891 kilajoules of energy.

Layman's terms: The natural byproduct of burning natural gas is Water Vapor and Carbon Dioxide. The beauty here is that neither of these is harmful to us. The downside is that if there is not enough oxygen in a room, it makes it difficult to breath and if there is too much water vapor, it can cause mold and mildew to grow. So, naturally, you want to make sure that you do not burn too much oxygen or create too much water vapor in any given area. Hence, the limitation on the BTUs allowed based on the cubic feet of space in a room.

Also of concern are lower levels of other byproducts that come from impurities in the gas. Also, when natural gas does not burn perfectly, carbon monoxide is produced instead of carbon dioxide. This is referred to as incomplete combustion. For the most part, ventless gas logs burn the gas almost completely, but they are not 100% perfect, which means that there are other potentially harmful byproducts that enter your home and must be controlled. That being said, it makes sense that smaller areas must use lower BTUs so that the percentage of carbon monoxide and other byproducts remains at a safe level. For example, even the small movement of air created by walking past the fireplace can cause a few molecules of Carbon Monoxide to be produced. Of course, when I say molecules, this is insignificant...but this happens often and the room is very small, it could then become significant..

The chemicals that are added to natural gas that make it smell like rotten eggs are also introduced into the room. It is typically the combustion of these additives that produce the odor which many people complain about when burning ventless logs. So, it is also important that there is enough ventilation to dilute the smell.

How does burning Ventless gas logs compare to burning Vented Gas Logs or Wood?
When you burn a wood fire or vented gas log in a wood burning fireplace, you have far more incomplete combustion of either the gas or gasses created by burning wood. This is what creates the lofty yellow flames that are taller and more alive than the flames you see on a ventless gas log. So burning wood or vented gas logs does in fact create a lot of smoke and emissions that you simply cannot have in your home, which is why you must have a chimney. Now because you have a chimney, the heat rises from the fire creating a draft that draws the smoke and other particulate matter up the flue, including the carbon dioxide and water vapor produced during the combustion process. The strong draft creates negative pressure, so fresh air literally gets sucked into your home through spaces between windows and doors, thus replenishing the oxygen without introducing water vapor or carbon dioxide.

Since vent free gas logs do not create such a draft (because the chimney is closed), the negative pressure is not created in the home and fresh air is not drawn in to replace the oxygen that has burned. For this reason, you will find that ventless gas log manufacturers recommend that you crack a window open when you are burning your logs.

I hope this helps clarify why it is so important to purchase the right gas logs for your fireplace.


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Answers to Recent Gas Logs Questions Posted To This Page
  1. Question #9527 - Posted: 2/2/2017 8:52:54 PM

    Gas Logs Question Model PL-CHCRG46-30-17P

    http://www.hansenwholesale.com/gas-logs/model.asp?SetModel=PL-CHCRG46-30-17P&LogSize=30

    QUESTION: 1. How large in diameter will the vent hose need to be for this type of unit?...Thanks, Frank

    ANSWER: I am assuming that you are referring to the size of the chimney. This gas log is designed to be installed in an existing wood burning fireplace that is capable of burning wood. If you do not already have a wood burning fireplace, then you cannot install this gas log without one. With that said, the minimum required vent depends on the height of the chimney. Please refer to this chart copied from the installation manual for specifics:


  2. Question #9526 - Posted: 12/29/2016 9:05:21 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/logsonly.asp

    QUESTION: I have a gas burning fireplace with a broken log. It was originally a wood-burning fireplace built in the early 1960s. It has a damper which is always open when burning. The fireplace was converted professionally to gas sometime before 2000. I converted it to remote-control lighting in 2010 using a reputable firm. Sometime later, one of the logs was dropped and cracked in half. It is held together by internal wires. I would like to replace one log rather than the entire set. Possible?

    ANSWER: It is possible, but that depends on the type of gas log set you have. If you can email us a picture of your gas logs, maybe we can find what you need. Email pictures to: gregt@hansenwholesale.com

  3. Question #9525 - Posted: 12/29/2016 8:58:26 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/best-gas-logs.asp

    QUESTION: I have a classic fireplace 26" in the back, 36" in the front and 26" depth. I live in a two story house built in 1935. The furnace broke and needs to be replaced. I'm looking for something to install in my fireplace to warm up the living room. I live in California so it has to be vented. What do you recommend to keep my room the warmest it can be? log set or would an insert be better?

    ANSWER: A vented gas log is not going to provide very much warmth for your room. Since you cannot install a ventless gas log in California, you are left with the option of installing a gas insert. I would suggest taking a look at the Real Fyre Direct Vent gas insert.

  4. Question #9524 - Posted: 12/29/2016 8:51:36 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/gaslogfaqs.asp

    QUESTION: i live in a 100 year old house and my fireplace was for coal and has a metal firebox. i have burned wood in it until last year, until we realized there was some leakage of smoke from the chimney upstairs. Would it be safe to use vented gas logs? Would we need to line the chimney like we would need to if we continued burning wood?

    ANSWER: Burning a vented gas log produces smoke just like burning real wood, so yes, you would have to reline or repair the chimney. I would suggest considering a ventless gas log so do not have to worry about smoke.

  5. Question #9523 - Posted: 12/29/2016 8:45:42 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/gaslogfaqs.asp

    QUESTION: what size and kind can I put in a woodstove "MORE HEAT" that has a door 20 BY 8.5 FIREBOX 28 BY 18 AND IS 12 INCHE DEEP and will they warm the stove enough to product heat with the fan.

    ANSWER: Unfortunately, you cannot install gas logs in a wood stove. Wood stoves are designed to operate with much lower draft than gas logs and the venting does not meet the minimum venting diameter. Even more, air tight wood stoves are designed to be burned with the doors closed, which is a definite no no when it comes to burning gas logs since they must be burned with the doors opened. There are other reasons why gas logs will not work in a stove, but I will not belabor that here. For more details, read more about Where Gas Logs Can Be Installed.

  6. Question #9522 - Posted: 12/29/2016 7:59:50 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/gaslogfaqs.asp

    QUESTION: I have a 24" peterson gas log set. The gas line in the fireplace is slightly larger than the connection for flex tube that leads to the gas burner. Can I add a smaller fitting to attach to the line leading to the burner?

    ANSWER: That should not be a problem unless the incoming gas pressure is higher than allowed by the installation manual, so you may want to check that.

  7. Question #9521 - Posted: 12/29/2016 7:53:16 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/rhpeterson.asp

    QUESTION: I occasionally turn our ceiling fan on low with the blades drawing the air upward while using our ventless gas logs. Our installation manual says a ceiling fan should not be used when the ventless logs are on. The flame of the gass logs appears to be unaffected. Is there a problem in having a ceiling fan on at the same time as the ventless gas logs? Thank you.

    ANSWER: Running a ceiling fan to destratify the air in your room makes sense from a heating efficiency/conservation standpoint, so I understand why you are asking your question. The responsible answer is that the owners manual says not to run your fan when you are operating your ventless gas log, so we cannot tell you that it is OK to do so. With that said, drafts can certainly cause ventless gas logs to NOT burn correctly and start producing toxic odorless Carbon Monoxide. It is safer for the manufacturer to tell you not to run your fan at all in order to avoid a potentially hazardous outcome rather than suggest that you can run it on a low speed in reverse with no ill effect. They cannot test the actual impact of doing so in your particular room. Their ultimate concern is to prevent any draft from affecting the flame. Whether you decide to follow the instructions is ultimately your decision...I will leave it at that.

  8. Question #9520 - Posted: 12/29/2016 7:31:40 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/vented-vs-ventfree.asp

    QUESTION: I do not really need the heat, and I have a fireplace already,but, the damper is either all the way open or completely closed. can I get that fixed so i can have it open part of the way so all the hot air does not go up the chimney thereby kind of making it silly to have one

    ANSWER: Technically, a vented gas log is supposed to be burned with the damper completely open. Plus, you cannot ever completely close the damper just in case there is a gas leak, so there is a clamp that is included with the burner system that gets attached to the damper to prevent it from ever closing completely. So if you do not really need the heat, then the way your damper operates is sufficient for a vented gas log. Whether you close the damper slightly to preserve some of the heat will not make much difference, you will get most of the heat from a vented gas log radiated into the room from the ceramic in the logs themselves. If you are really concerned about getting heat (which you say you are not), then you should consider buying a ventless gas log.

  9. Question #9519 - Posted: 12/29/2016 7:02:36 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/default.asp

    QUESTION: Question - Are there burners or logs that are better for use with propane to achieve the best flame presentation? Currently my propane flame in my FP is not as robust as I would like. Just curious if there are options that are better for propane specifically.

    ANSWER: Whether you are burning natural gas or liquid propane, each type of burner is configured for optimal performance for the gas you are using. So you would need to make sure you order a burner system for Propane gas, otherwise it will not perform properly. With that said, if you want the most robust flame, we would recommend either the G4 or G45 burners since they operate at the highest BTU (the most flame). However, neither of these may not be the best choice for your particular fireplace depending on the type of fireplace you have and the dimensions. Please send us some pictures of your current setup so we can see what you have and make further recommendations. Email pictures to: gregt@hansenwholesale.com.

  10. Question #9518 - Posted: 12/29/2016 6:53:51 PM

    Gas Logs Question

    http://www.hansenwholesale.com/gas-logs/gas-log-burn-cost.asp

    QUESTION: Where do I find a remote control for my gas logs? And how much?

    ANSWER: Gas log remote controls are not universal in design. They are made as a transmitter and receiver combination, the receiver usually a built-in component of the gas log valve and burner system. So if you have an existing gas log with a remote and you are looking to replace a remote that is no longer working, you are going to need to contact the manufacturer of the gas log system you own and see if they can supply you with a replacement remote. If you are wanting to add a remote control to an existing gas log, that is a different story. In most cases, you will need to replace the entire burner system with one that is remote capable. Replacing the burner system may also require you to replace the logs since not all logs are compatible with all burners. If you email us some pictures of your fireplace we may be able to offer more direct advice. Send your pictures to: gregt@hansenwholesale.com...or just give us a call at: 1-800-201-1193.

THE END

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