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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!

Width  Length  Height    
x 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.