• Welcome to the new and improved Building Code Forum. We appreciate you being here and hope that you are getting the information that you need concerning all codes of the building trades. This is a free forum to the public due to the generosity of the Sawhorses, Corporate Supporters and Supporters who have upgraded their accounts. If you would like to have improved access to the forum please upgrade to Sawhorse by first logging in then clicking here: Upgrades

Garage with air infiltration less than .40ACH

R

retire09

Silver Member
Joined
Feb 19, 2010
Messages
365
Location
Alaska
I have an energy rater telling me that the 2 car garages built today with 16' overhead doors and a 6" gas vent thru the ceiling have been tested and have less than .40 air changes per hour and that combustion air openings must be calculated per IFGC 304.5.1.

I know nothing about an air infiltration test, but is it possible that a 2 car garage of only about 4000cf of air space with a door to the house, a door to the outside, a 16' overhead door and a 6" diameter hole in the ceiling for gas ventilation could test that tight?
 
I'm assuming you mean .4 ach at 50Pa. I find that really hard to believe. I would want to see some data supporting his claims, or have to rater preform a blower door test demonstrating the <.4 ach.

Combustion air openings are to provide air when you have a fuel burning appliance that would otherwise depressurize the building, pulling combustion air through the building envelope. If the car is not direct vented to the exterior (would like to see that) the depressurization will not occur. The only thing I would recommend is to ensure you have a good gas barrier between the dwelling and the attached garage to prevent carbon monoxide from leaching into the dwelling unit. Or just open the garage door when you start the car.
 
Seems to me the garage is outside of the energy envelope and therefore exempt from blower door test.

I do not think a garage is proper area for obtaining combustion air.

I have seen where people run car in garage with open door, CO still entered the house because of the stake effect, or when they open the door to the house the negative pressure in the house pulls the CO in.

It is never a good idea to run any engine in a garage regardless of the doors that are open.
 
TheCommish said:
Seems to me the garage is outside of the energy envelope and therefore exempt from blower door test.
Click to expand...
That was my thought as well.

TheCommish said:
I do not think a garage is proper area for obtaining combustion air.
Click to expand...
I think they are stating that combustion air is required to be supplied to the garage, not that they are supplying it from the garage.
 
Tell him to bug off. :)

The attached garage has nothing to do with the building thermal envelope.

Uncle Bob
 
The garage has 80,000 Btus of gas appliances installed that are allowed by the standard method of 1000BTUs per 50cf of space.

The energy raters are insisting that combustion air openings are required for life safety based on their claim of less than .40ACH in the garage.

This a heated and insulated garage in Alaska and I'm trying to determine if this claim has any merit.

The garage is extremely well separated from the house with 6mil poly and insulation along with a 20 min rated self closing door

I would rather not vent heated spaces to 30 below 0 outside temperatures.

Does this sound reasonable to anyone?
 
retire09 said:
The garage has 80,000 Btus of gas appliances installed that are allowed by the standard method of 1000BTUs per 50cf of space.The energy raters are insisting that combustion air openings are required for life safety based on their claim of less than .40ACH in the garage.

This a heated and insulated garage in Alaska and I'm trying to determine if this claim has any merit.

The garage is extremely well separated from the house with 6mil poly and insulation along with a 20 min rated self closing door

I would rather not vent heated spaces to 30 below 0 outside temperatures.

Does this sound reasonable to anyone?
Click to expand...
In the Canada energy codes it considers attached garages outside of the building envelope regardless of heating and insulating within the space. However, it also requires HVAC equipment to be installed in a conditioned space.

Can they prove < .4 ach? If not I would not require the installation of combustion air openings.

I think the raters are on a power trip.
 
If they preformed a blower door test then they had to seal up the 6 inch combustion air vent you have for the gas appliances. There is no way they could have gotten a .40 ACH with a 6 inch open hole. A 6" will flow about 100 CFM x 60 = 6,000 CFH that is 1.5 air changes per hour not .40 as they claimn.

To quote UB

Tell him to bug off. :smile:
Click to expand...
 
You must log in or register to reply here.
Top