Comments on: Size Matters — How Big a House Can You Test with One Blower Door?

By: ted kidd

ted kidd — Tue, 12 Mar 2013 04:58:56 +0000

I don't know who "Debbie
I don't know who "Debbie" is, but I think I like her.

CG too.

But it is most reassuring to do the numbers yourself. I have access to a similar sized house, and own a double drape. So I think when the weather get's better I'll borrow a second fan and test both ways.

I've always felt that once the number gets huge, accuracy of the cfm50 number becomes less critical. I do write down the actual Pa as well just for reference.

Nate, if you didn't get to 50, what number DID you get to? Anybody think it make sense to measure to that number as well as 50 when he is done?

By: Ryan Shanahan

Ryan Shanahan — Thu, 28 Feb 2013 04:43:32 +0000

Nate, Point taken as well. I
Nate, Point taken as well. I work exclusively with new contruction. I tend to see things through that lense. Keep fighting the good fight!

By: Ryan Shanahan

Ryan Shanahan — Thu, 28 Feb 2013 03:28:14 +0000

It blows my mind (pun
It blows my mind (pun intended) that the same crowd (the energy geeks) are trying to get blower doors, duct blasters, and bd frames small enough and/or tight enough to test Passive Houses accurately are simultaneously trying to figure out how many BD's we need to test 10,000 sq ft houses. Could there be a bigger disconnect?

By: CG

CG — Wed, 27 Feb 2013 16:03:17 +0000

If you really want to see the
If you really want to see the accuracy play out, simply take cfm50 readings with @50 Pa turned on and run the gauge up from 10 to 50 Pa and not the values you get along the way. Different houses will give different results depending on what the hidden n is for that house. If you have no time for any other pursuits, change the n value in the gauge and you will find a value that gives the same results at all pressures. You will now be an expert.

By: Colin

Colin — Wed, 27 Feb 2013 15:56:08 +0000

My message went poof in the
My message went poof in the middle.
Accuracy of @ 50 Pa
1. decreases as distance between the test pressure and 50 Pa increases.
2. decreases as actual extrapolation value departs from the preset value of 0.65 in all gauges. If you have a leaky house, this value can be set to 0.55 to get better results. A feature on the Retrotec gauge and one that is not understood.
3. when it's windier the error will increase also.

Rule of thumb, don't go below 20 Pa and you'll be within 25% most of the time. Maybe 35%. If it leaks that much, it is either bad or super bad and needs to get fixed.

By: Chris Bellanca

Chris Bellanca — Wed, 27 Feb 2013 05:57:37 +0000

I did a few bd's on a 10,000
I did a few bd's on a 10,000 SF national register house a while back. I could not get pressure on any of the tests and the varied cfm50 #'s didn't provide me any confidence in the readings. As we installed improvements and aligned the air barriers with the insulation, we did see marked improvements in the utility bill metrics though. They did not align with our pressure tests.

By: Nate Adams

Nate Adams — Wed, 27 Feb 2013 02:30:52 +0000

I am personally not a big fan
I am personally not a big fan (no pun intended, oh, ok, you got me) of extrapolation. From my experience, old homes over about 3000 sf are pushing the limits that I trust around 7000-8000 cfm50.

We just finished a 10,000 sf home built in 1913, and it had a 9930 blower door. As leaky as those homes usually are and as large as it is, I just can't see 1cfm50/square foot. That is typically close to Building Air Standard (sorry to bring it up, but it's still something to gauge against.)

My guess would be this house is closer to 15,000-20,000 cfm50. The program I work with only sends out 1 door, and I only have 1 door. I told the homeowner not to expect a big change in the number because I don't think it was accurate to begin with. I don't mean to be a wet blanket here, by the way, I'm just curious:

Do the blower door manufacturers out there have any verifications where extrapolation was done vs. 2-3 fans to get a real number? Do they match up? I'm betting Michael Blasnik has something... =)

I grant you there aren't many houses out there like this, but we have done 2. And yes, I should buy another blower door...

By: Debbie

Debbie — Tue, 26 Feb 2013 23:18:10 +0000

so once again, the answer is
so once again, the answer is
it depends.

if you invest in a good caulk with a long life, install it properly it lasts. install cheap short life caulk improperly ...then it is a band aid.

insulation with no air sealing is a waste of money.

caulk is an excellent way to air seal leaks in homes
with above considerations.
just as mastic is an excellent sealant for ductwork.

the right product for the leakage site is what makes the work last.

By: Tapani Talo

Tapani Talo — Tue, 26 Feb 2013 21:05:59 +0000

Caulking is like bandaids.
Caulking is like bandaids. People think they have done something, when they really need 90% improvement with proper insulation to benefit and be safe and comfortable with no utility costs to talk about.

By: Tapani Talo

Tapani Talo — Tue, 26 Feb 2013 20:51:56 +0000

Even in NEW construction, I
Even in NEW construction, I have to personally walk the contractor through every window and other openings, make sure that vapor barrier is continious. Older buildings - all frmed openings simply OPEN.