# cumbustion air

I want to calculate the indoor basement cumbustion free area. the total basement is 800 sq. computer room ,office bath,entertainment area. the mechanical room is at the entertainment area. I want to know when i calculate free area sq. for sizing transfer grills for the mech rm. Do I calculate the whole basement or just the entertainment area as indoor free area ?
Thanks.
Charlie

Does each room have doors? If so, then only the entertainment area. If not then entire basement. Might be a typo, but it is actually cubic feet you need, not square. Formula for combusiton air is h x w x l x 20 = amount of combustion air in the area.

I was taught that it was H x W x L x 3. That value must be greater than the combined BTU of all the gas appliances in the confined space.

The formula I was taught was from an appliance/HVAC class taught by Peoples Gas as they use this formula on CO calls, service work, etc.

Mark, the additional material is good info on how much combustion air is needed.

Watch a CMI perform some calculations of confined spaces for hot water tanks and a gas-fired heating system, in a studio and on-site in a house. http://www.nachi.tv/ppv/8

Calculating confined spaces and combustion air is way beyond the scope; however, discovering safety, health, and fire hazards are not.

After watching this video, an inspector should feel comfortable commenting upon confined spaces and using a narrative such as, “I have not made any calcuations relating to confined spaces and combustion air for the appliance; however, there may be a safety hazard here. We recommend having a professional inspect further and make any necessary corrections.”

Take a look at this to see how easy (NOT) it is to calculate combustion air requirements.

http://commerce.wi.gov/SBdocs/SB-UDCApril01SummaryWorksheet.pdf

Here is the one I was originally looking for:
http://www.houseofcraig.net/combustion_air_calc.html

Wow. That’s great. Thanks.

When I was performing an Infrared Thermography Inspection in the IR video, I was concerned about how much power (cfm) the whole house fan had. I didn’t want to suck in CO from fuel-fired appliances. I didn’t know the cfm for the fan.

The problem with both of these calculations is that they give sizes for ducts connected to the outdoors for combustion air. If the system is simply passive combustion air supply, when the outdoor hoods are in the lee of a strong wind (read high negatiove pressures), house air will be sucked out of them, not combustion air supplied to the appliance room!!!

WETT, Inc in Canada has a video of smoke being sucked out of the dedicated, directly connected combustion air duct (uninsulated metal) installed between wood floor joists, while in the firebox, the flame burns down into the firewood with combustion air being supplied by the chimney!! This was a situation where it was a WETT certified installer and a UL/ULC certified zero clearance “airtight” heating fireplace (read: stove in fireplace form). This was not a training setup but a real life installation!!

I think the most important aspect of this thread is to assure you do not spell combustion the way it is spelled in the thread title. Just a small observation on my part.

Jeez…us!! That could lead to a lawsuit some places.