GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Blower door test

housebldr | Posted in General Questions on

I recently built myself an ICF home, approx. 2,500 s.f. x 2.

I used ICFs from footer to roof and insulated the attic with approx. 10” of open-cell sprayed on the rocked ceiling. I was diligent about foaming all possible leak points.

I had a blower door test done and was told at 50 pascals it had a natural ach of .04. Does this seem possible?

It seems extremely tight!

I did install a stand-alone HRV system. Will this provide the make up air I need for dryer & range vent? The HRV is set up to provide ventilation for baths and pantry. My understanding was the HRV provided a balanced system. Will this throw it out of balance when a vent is running?

We did use the Flir camera and found very few leaks. I am in zone 5.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. STEPHEN SHEEHY | | #1

    Kevin. You number is probably off by a factor of ten. .4ach/50 would be very tight, lower than passivhaus. .04 is probably not achievable.

    An hrv doesn't provide make-up air. What system did you install? The typical hrv exhausts air from kitchen and baths and provides fresh outside air to bedrooms and living rooms. Mine has a boost option that increases ventilation on a timer if needed after a shower or to vent extra cooking odors, but if you have a big kitchen vent, you may need a source of make-up air or just open a window.

  2. user-1072251 | | #2

    Natural air change and ACH@50 pascals are different. While I cannot tell you how to go from one to the other, others here can. Do you know what the manometer reading was?

  3. GBA Editor
    Martin Holladay | | #3

    Rules of thumb for calculating ACH(natural) vary by climate. In Minnesota, ACH(nat) equals approximately ach50 divided by 17, while in Florida, ACH(nat) equals approximately ach50 divided by 30.

  4. charlie_sullivan | | #4

    The problem with what you were told is that "at 50 pascals" and "a natural ach" are conflicting statements. If it's at 50 Pa, it's not natural. Probably what they meant to say is that from the ACH_50 result, which is probably about 0.6 to 1, they estimated that ACH_nat is around 0.04. But there are more and less sophisticated ways to estimate the ratio, and even the most sophisticated can only give rough estimates. So the ACH_50 number would tell use what was really measured.

    But regardless, the result means you did well at making a tight house.

    If you have combustion appliances, the range hood and dryer could make them backdraft. If you don't, I wouldn't worry too much about the makeup air issue. You could crack a window when you operate them and they might work better, but they will probably still work without cracking a window.

    You might consider one of the two ventless heat pump dryers that are now available in the US, especially if you haven't yet cut a hole in the wall for dryer vent.

  5. GBA Editor
    Martin Holladay | | #5

    Q. "I did install a stand-alone HRV system. Will this provide the make-up air I need for dryer & range vent?"

    A. No. An HRV is not a makeup air appliance. For more information on this topic, see Makeup Air for Range Hoods.

  6. GBA Editor
    Martin Holladay | | #6

    By the way, 10 inches of open-cell spray foam provides an R-value of about R-37. That doesn't meet minimum code requirements in your climate zone. You want at least R-49 -- so it would probably be a good idea to blow some cellulose on top of the cured spray foam.

  7. housebldr | | #7

    Charlie, you are correct,they tested at 50 then gave me the results in "natural" ach sorry I did a poor job of wording that.Bob-not sure what a manometer is but when the house was at 50 pascals the guage on the blower showed 412 cfm is that what you mean?Stephen- my hrv is a fantech,I have the boost option as well.Martin- I realize i am below the recommended r-value but most spray foam guys tell you to throw r-value out the window when talking spray foam with an air tight seal (I actually had a hard time finding one that would spray more than 5-6'' they all said it was a waste of money) but I wanted my ceiling joists covered to prevent thermal bridging.Do you have any real world tests that show r-value with spray foam is more about thickness and less about air movement? There seems to be a lot of debate about this. Thanks for all the replies!

  8. user-1072251 | | #8

    yes; 412 indicates a tight house.

  9. GBA Editor
    Martin Holladay | | #9

    Q. "Do you have any real world tests that show R-value with spray foam is more about thickness and less about air movement?"

    A. The short answer to your question is: (a) No matter what type of insulation you install, you need to pay attention to airtightness; and (b) R-value is R-value, and (all other factors being equal) R-37 will not perform as well as R-49.

    Here is a link to an article that discusses these issues: It’s OK to Skimp On Insulation, Icynene Says.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |