Friday after the insulation was complete Ken did a blower door test. It’s taken me 2 years of research to get to under stand what XX ACH50 means, and what tight mean for a house. For those who are just learning I’ll try to explain.
You start by closing the house up tight, windows & door closed, plumbing vents, sump vents and so on are taped shut. A box with a fan is mounted in the front door. See photos.
The fan is run to depressurize the house to 50 Pascal’s. The fan is controlled by a device that measures the difference in pressure of the outside to the inside of the house. It was having trouble holding on the 50 Pascal’s, note the black disks in the holes around the fan. Ken had to add a couple more to get the fan to settle down. My guess that is because the house is so tight.
There are many articles online about house tightness and blower door testing. As a reference for you, the 2015 Code will require all house to achieve a “3 ACH50” . That’s 3 full house Air Changes per Hour at 50 Pascal’s of depressurization. NJ has adapted the 2015 code effective March 2016, but not the 3 ACH50 requirement. Pulte the 4 largest builder in the US has announced they will build a High performance model in CA this spring with a 3.5 ACH50 target. It is the future, but the future isn’t here in a big scale yet.
Our reading Friday was an 0.5 ACH50. I think that is about as tight as a house can get. That means the fan can only suck half the full volume of the air of the house in an hour. Here is the gage. It shows at -50.1 Pascals the fan is sucking out 401 CFM, the full house volume is 46,251 CF. All I can say is success. That’s 600% better than code. ( and one builder told me I’m reading to much) 🙂
Build Tight – Ventilate Right
One of the most important thing in building a Energy Efficient house is building it Tight”. The tightness of a house in measured in Air Changes Per Hour. This measurement is done by depressurizing house to 50 Pascal’s. A Pascal is a measurement of vacuum, it used to me measured in inches of water in a column. It is accomplished by putting a big fan in the doorway and sucking the air out of the house until you get to 50 Pascal’s then measuring the CFM of the air leaving the house..
The 2015 building code calls for 3.0 ACH50 to give you a reference point. We test our house at 1.0 ACH50 last week after the closed cell foam was sprayed. I was hopping for less, maybe a 0.5 ACH50 or lower, but as I said in another posting my design with the roof angles and changes didn’t help.
I think we are at 99% sealed at 1.0 AC50, but I’d like to get to 100% I asked a few people for tips on finding the leaks. The best suggestion was to warm the house to apx. 20 degrees above the outside temp. displeasure the house to 5 Pascal’s and using a thermal imaging camera to see the cold air leaking in. Using the torpedo heater I was running up the temp waiting for Ken to come. I got the idea to use my laser thermometer see if I could see a temp different any where that may show up where the leak was. It worked. Where we suspected the leaks were I saw a 3 to 5 degree difference is wall temps with in a foot circle. In other words, the wall temp was 65 and moving just 6 to 12 inches it would drop to 60 to 62. The only place this happened is where we suspected a leak was, no where else. Ken had a plan to fix the leaks so I just told him to proceed.
We will do another blower door test when Ken completes the cellulous installation.
Once the closed cell foam was applied the house should be tight, so we could do a blower door test.
The front door is blocked and a fan in installed. The fan sucks the air out of the house to a difference the house pressure at negative 50 Pascal. Pascal is a measure of pressure. A typical existing home might leak at the rate of 15 air changes per hour at 50 pascal. Our test It came out 780 CFM at 50 Pascal or 1.0 ACH50. That’s 1 air change an hour at a negative 50 Pascal. That’s tight, but……I was hopping to get it lower, a 0.5.
To achieve a Passive House rating 0.7 ACH50 is the target. I’m not shooting for a Passive House certificate but I’d like to get to a 0.5 ACH50. But most Passive Houses are box on box construction. My house is far from a box on box. In going over the house it was easy to see how all the roof lines make it extra hard to seal the house as if it were a box on box.
Finding leaks is more art than science. The fan is reversed, pressuring the house. We then look at likely places for leaks hold a smoke wand in the area looking at how the smoke behaves. We found some small ones but no big holes. We are going to do some research and give it another try before the cellulous is installed.
Yesterday Don from ReVireo came out to do the first blower door test. I was not sure what to expect, being my first blower door test I’ve seen. We had sealed the house the best we could, but because of the big windows, bigger that a sheet of sheathing, I was sure there would be some leakage.
I think the testing at this point is more “art” that “science”. First Don tried the small fan, but that couldn’t move enough air, so he switched to the bigger one. With the vacuum setting, the fan sucking air out of the house, we got a 1.9ACH50. Which said the house had some small leaks. We switched to the pressurizing setting, blowing air into the house, and took a smoke wand to look for any leaks. Had trouble finding any, none on the first floor. Only one in the basement: the basement door, across the bottom, was loosing air, but that stopped when I locked it. On the second floor we found leaks along the main ridge board and the dormer ridge board. Which will get sealed a little later.
With that finding I consider the test worth doing and of value. Now off to windows, doors, roofing & siding. Shortly it will look like a real house.