# Infiltration factor for heat loss calculations

| Posted in General Questions on

Good Morning, My first question relates to the infiltration factor in Heating calculations. Is there a direct correlation to a specific Air Change per hour, for example; .6ach50 = .12 infiltration factor. I have been trying to find some information to get a close estimate on our plans.
Second question, which I have a feeling is subjective to building conditions, is what is a good air change per hour for a pretty good house. Air barrier being 1/2″ sheathing gaps and nail holes filled with prosoco seam and filler followed by R guardCat5.  Accoustical sealant on foundation plates, sheathing seams, etc. Thank you for your time.

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### Replies

1. | | #1

This should help:

https://higherlogicdownload.s3.amazonaws.com/ACCA/c6b38bda-2e04-4f93-bd51-7a80525ad936/UploadedImages/Infiltration%20per%20Blower%20Door%20Test%20Oct2016.pdf

Note that a) it's highly variable (with wind, etc) and b) it depends if you are interested in peak load, average load or minimum airflow (perhaps useful with ventilation analysis).

2. Expert Member
| | #2

Nick,
Are you asking whether or not you can extrapolate the amount of BTUs lost from air infiltration as indicated by a blower door test?

If so, I don’t think this is possible….

The reason for this is that not all air leaks in a house will result in the same amount of heat loss. For instance, due to the stack effect, a hole in your air barrier at the ceiling will lose a lot of heat. If there are also holes around the foundation (specifically where it meets your walls), then the heat loss from the ceiling will be magnified further as the stack effect intensifies. If your ceiling and foundation are air tight but your walls or windows are leaky- you may not actually lose that much heat. (Although there may be comfort issues, air quality issues, etc.)

There is also the issue of some materials recovering some heat as it exits the home. This "warms up" the area around the air-hole and therefore reduces the amount of heat loss. Just as a blower door test does not account for the the location of air leaks, it also doesn't account for the materials present at the site of the air-leaks.

Also- (If I recall correctly) blower door tests run at 50 pascals are equivalent to a 25 mph gust hitting your home. Under normal circumstances, the house will experience far fewer air changes per hour.

In terms of assigning a heat loss figure for air infiltration- I think you are just going to have to wing it!

1. | | #3

Rick,
Thanks for the reply. I was trying to do some preliminary Heat Loss Calculations to work on heating options(i.e radiant heat or mini splits). I was also under the impression, the infiltration factor, was somewhat subjective to the building methods. I was curious if there was a close number to plug into the calculations. I also didn't want to do the calculations and be completely off.

3. | | #4

Nick,
The benchmark for blower door tests is the "Passive House" requirement of under 0.6ACH@50pa. IMHO a "pretty good house" should be under 1.0ACH@50pa. As I understand your question it is how does this impact heat loss calculations? Houses this "good" need mechanical ventilation to assure indoor air quality and the ventilation will result in additional heat loss or gain. The document Jon R pointed us to, in his reply, suggests that the infiltration, for heat loss/gain calculations is about 1/18 the blower door number but mechanical ventilation needs to be added.

1. | | #6

Jerry,
Thank you! I was having trouble with the link above in first post. The numbers help give a starting point for the calculations. Again thank you.

4. | | #5

Hey Nick,

In regards to your second question, when I was at Fine Homebuilding we were regularly seeing architects' and builders' projects, that I consider pretty good houses (though often they had expensive finishes) hitting Passive House levels of air changes. The thing about air sealing is that it doesn't have to be expensive, it just requires a good plan and diligent follow through. Knowing what to do in tricky areas like the mud sill, or a chimney, or penetrations in the upper-floor ceiling is super important. Try these links for some more info:

https://www.greenbuildingadvisor.com/article/questions-and-answers-about-air-barriers

https://www.greenbuildingadvisor.com/green-basics/air-barriers

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