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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. Some cities do not allow ventless gas logs to be installed in bedrooms or confined spaces, others do not allow ventless gas logs to be installed at all. Check local building codes for any restrictions or conditions regarding ventless logs before you purchase or install them. Use of a Carbon Monoxide Detector is recommended with ventless products.

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 Questions Posted To This Page

  1. Posted: 1/4/2010 8:56:33 PM

    I currently have q vent free gas log. I can not stand the smell. Do certain brands of logs not smell?

    Answer: ALL ventless gas logs smell to some extent. Some brands certainly smell worse than others and can smell so bad that they are simply intolerable. It is mostly a matter of the quality of the burner system. Cheaper log sets sold at home centers and mass merchants are the worst. The ventless logs that we sell made by R. H. Peterson are about the best you can get...but they still produce a noticeable odor. We make this very clear throughout the many resources on our website just so that our customers are well aware of what they are getting into should they decide to purchase a ventless gas log.

    For information, please read the following pages on our site:


  2. Posted: 1/2/2010 1:57:14 PM

    I? want to be as green as possible. Are gas logs a good green investment

    Answer: Burning Peterson gas logs instead of real wood is in fact the ultimate Green choice when it comes to using your fireplace. Burning wood can release anywhere from 300 to 2000 times more particulate matter into the air and 200 times more carbon monoxide! R. H. Peterson had OMNI laboratories do some non-biased tests comparing burning real wood to burning Peterson gas logs. You can read the findings of this report here: Peterson Gas Logs are a Green Choice

  3. Posted: 12/26/2009 5:11:49 PM

    I am looking to purchase ventless gas logs for an already existing woodburing chimney. There is a sticker on the side of my fireplace "box" that says it is designed to handle logs not to exceed 26,000 BTU. Based on your BTU formula however, the room is EXTREMELY large as it joins with the kitchen and dining room and has cathedral ceilings throughout all three joined rooms, approximately 963 sq feet total. Why would there be such a small BTU fireplace for that space and which should I follow?

    Answer: Are you sure it is a woodburning fireplace? Also, does the limitation say specifically Ventless gas logs or does it specify anything else? Most wood burning fireplaces do not have such limitations on BTUs. What is the brand and model number? Ulitmatly, you must not exceed the BTUs listed on the fireplace. As to why a fireplace with such limited BTUs was installed in your home, well that would be a question for the developer or architect who designed the home.

  4. Posted: 12/17/2009 3:15:30 PM

    IM LOOKING TO HEAT A ROOM 30FT X 30FT X 10FT I WOULD LIKE TO USE VENTLESS GAS LOGS OR ANY WAY WITH PROPANE WITHOUT A VENT GOING OUTSIDE. I WOULD LIKE TO HAVE A BLOWER ON IT.WHAT DO YOU RECOMMEND...

    Answer: If you insert your dimensions into our Gas Log BTU Calculator, you will find that the Maximum allowed BTUs for a room your size is 180,000. However, the maximum amount of BTUs allowed by any Ventless gas log is only 40,000. So you can see that your room can handle 4 times the amount of BTUs that any Ventless gas log is able of producing. What this means is that you simply cannot heat that much space with a ventless gas log.

    Even more, ventless gas logs are not to be used as the sole source for heat and they cannot be burned for more than 6 hours per day total.

    Ultimately, you simply cannot heat your room with any ventless gas log set, but you will still enjoy the warmth when you are in the near vicinity of the fireplace.

Read all Questions & Answers >>

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