I've had my blower door test today - I have : 27,000 cubic feet of space Pulled 950 CFM @ 50 pas How can I convert this to ACH? I've searched and am stumped. I would like to find out as well as know if I require a HRV - It seems my air sealing has paid off !!! Thanks in advance! Dave.

( 950 CFM / 27000 CF ) * 60 Min/ 1 hour = 2.11 ACH50.

This is pretty tight, I thought the threshold for mechanical ventilation was around 5 ACH50.

Wow DJV that's some amazing tightness you have there. It's not Passive House Standard, but it's still great considering that the average house is around 4 to 5 ACH50. You should submit some details on here about your project or at provide a link to the post if it's already on here. Good job man. Air sealing really does make a huge difference.

The 2012 IRC requires a blower door test with < 3 ACH @ 50 pascals

Passive House standards are < 0.60 ACH @ 50 pascals

Quite a dramatic difference.

What kind of construction did you use (wood frame, ICF, SIPs)?

Was this blower door test done prior to drywall?

ACH50 is such a flawed measurement. For example, a crack in an upper floor ceiling will have many times more ACH-nat flow than a mid level crack (due to the differences in stack induced pressures). And ducted HVAC has a huge effect on ACH when it is operating.

Using a tracer gas with the HVAC operating and the house at 30F more than ambient probably makes sense. Call it ACH-typical (depending on climate). Wind and wind blocks should also be accounted for.

Posted By HVAC-Engineer on 04 Oct 2013 10:34 PM
Wow DJV that's some amazing tightness you have there. It's not Passive House Standard, but it's still great considering that the average house is around 4 to 5 ACH50. You should submit some details on here about your project or at provide a link to the post if it's already on here. Good job man. Air sealing really does make a huge difference.

Thanks I am in the process of drywall now. We have a home built in 1890 that was 1080 sq ft 1 story home. We gutted the home and added a second story, creating a 2400 sq ft home. We continued the 9ft ceilings throughout. We have a mix of basement that was dug out and lowered and crawl from previous additions as the 1890 portion was about 500 sq ft originally The exterior walls of the basement were spray foamed with 2" cc. This was done while the HVAC was roughed in with registers but no duct ran. I did this to not miss any spots from duct in the way of properly coating the rim joist area. The first floor is and was 2x4 construction and we continued this through the second floor. We have 2" cc sf on all walks and 3" cc sf on all roof areas. We foamed all doors and windows ( new) and made no electrical penetrations from floor to floor in the exterior walls. We caulked all top and bottom plates as well as and double joist that foam was not utilized. There are 3 exterior doors in our home and the thresholds are all in the bottomed out position. These were my air leaks. Since we are rocking and taping now we left them and once they are adjusted it should make the house even tighter. I have no idea how much but that's all we could find when the blower was running. The test was conducted without rock as I needed to make sure we were tight. I'm running a geothermal system and need the tightness to keep the system in its operating range. We pulled 7000 cfm before on the 1080 sq ft home ( not counting basement ) and it was reflected in $500/month electric bills during the summer when the AC was cranked and running solid. This should be a comfortable home with less drafts then before and have lower utility bills with more then double the size. The HRV/ERV is my next move and I need to determine what size I need and where to run it I doubted we could get the house this tight but it's a good thing. Edit. Where are my paragraphs ?

You can debate what the value of ACH 50 vs ACHn or leakage relative to exterior surfaces area, but reducing cfm50 from 7000- 950 is a great result. As far as what you need for mechanical ventilation goes, you need to figure out what standard is code where you live. For arguments sake, I will use ASHRE 62.2 2010 which is required under the 2009 IECC The HRV should have a maximum flow rate calculated as (7.5 cfm* number of occupants) + 0.01* sf floor area. The number of occupants is calculated as # of bedrooms+1 so assuming it is a 3 bedroom house at 2400 sf , 7.5*4 +2400*0.01 = 54 cfm continuous ventilation. Technically you could derate this value a little based on the blower door test, but I would not bother. I would probably spec a HRV that had 2-3 times that capacity on high setting and pair it with a controller that allows multiple fan duty cycles and speeds. I find I need higher flow rates in the summer then winter to be happy. I notice if I leave the hrv off, the house smells stale. I also crank the hrv on high when my dog has gotten wet or after cooking stuff that stinks up the house. I like the variability. Cheers, Eric

Thanks.

When we started demo we found newspaper rolled in the walls (1926 ) and some walls with no insulation.

We also had very limited house wrap - mostly tar paper and such. With misc 1" x misc boards as exterior wood that was under wooden siding. So the house was leaky to say the least

Where are my paragraphs ?

There are different kinds of carriage returns going back to the beginnings of computer science and different browsers deal with them differently. If you are using Internet Explorer, you need to go into IE Tools and look at 'Compatibility View' or some other such similar thing.

Posted By eric anderson on 05 Oct 2013 06:48 PM
You can debate what the value of ACH 50 vs ACHn or leakage relative to exterior surfaces area, but reducing cfm50 from 7000- 950 is a great result. As far as what you need for mechanical ventilation goes, you need to figure out what standard is code where you live. For arguments sake, I will use ASHRE 62.2 2010 which is required under the 2009 IECC The HRV should have a maximum flow rate calculated as (7.5 cfm* number of occupants) + 0.01* sf floor area. The number of occupants is calculated as # of bedrooms+1 so assuming it is a 3 bedroom house at 2400 sf , 7.5*4 +2400*0.01 = 54 cfm continuous ventilation. Technically you could derate this value a little based on the blower door test, but I would not bother. I would probably spec a HRV that had 2-3 times that capacity on high setting and pair it with a controller that allows multiple fan duty cycles and speeds. I find I need higher flow rates in the summer then winter to be happy. I notice if I leave the hrv off, the house smells stale. I also crank the hrv on high when my dog has gotten wet or after cooking stuff that stinks up the house. I like the variability. Cheers, Eric

2-3 times, if you don't mind the noise... My EV130 does a nice job in 2100sq.ft. just the three bathes exhausted. HRV/ERV takes some design consideration beyond the suggested CFM.

Like where to put the inlets and outlets?

My EV130 does a nice job in 2100sq.ft. just the three bathes exhausted

How does one know? For example, what verification is there that CO2 levels in a closed door bedroom aren't too high with such a design?

Posted By jonr on 07 Oct 2013 11:21 AM

How does one know? For example, what verification is there that CO2 levels in a closed door bedroom aren't too high with such a design?

How does one know?

When one begins to get light headed, begins to have muscle twitching and chest pain and then passes out due to CO2 poisoning.

In all seriousness, one can test the air levels of CO2 by having a Carbon Dioxide Meter. They sell for $150 - $300+

I suspect that an inspector might say "show me that this bedroom has the required 10 CFM of ventilation". And with the door closed and no ducts, it probably doesn't. With just a supply duct - maybe.

Posted By jonr on 07 Oct 2013 06:58 PM
I suspect that an inspector might say "show me that this bedroom has the required 10 CFM of ventilation". And with the door closed and no ducts, it probably doesn't. With just a supply duct - maybe.

I wonder if they would accept an undercut door?

Your are giving the inspector too much credit. In residential the air changes are not confirmed. As for how one knows, the nose knows.

"Your are giving the inspector too much credit. In residential the air changes are not confirmed."

Yes and no. Many inspectors are undereducated for the task and many are indifferent to it. So yes we may be giving inspectors too much credit air balance reports or airchanges are not confirmed as you said. However many inspectors don't know to look.

As envelopes tighten and ductless systems grow in popularity, the code and inspectors are going to have to catch up.

I was reading about a homeowner who did a blower door test on his home and got 20 ACH, that was an improvement since his last test with was 32 ACH. No kidding, it was THAT BAD.

I wonder if they would accept an undercut door?

Data is available for supply only at 10 CFM. As I recall, it was something like 1/4" under the door and you will still get some pressurization of the room. In a closed door room it is best to use a supply and a return, both with dampers.

"Data is available for supply only at 10 CFM. As I recall, it was something like 1/4" under the door and you will still get some pressurization of the room. In a closed door room it is best to use a supply and a return, both with dampers."

There is code and then there is opinion and data. Unfortunately they are not always on the same page.