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Air infiltration heat losses - Page 2

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Posted by Morris Dovey on December 22, 2007, 6:55 pm
Jeff wrote:

|    Lets say we have a 10,000 ft^3 house. If it is exchanging half
| that per hour that is 83 CFM. What total size air hole would that
| be going through?

Hmm - that's about enough air to fill a cube between 4 and 5 feet on
an edge. I'd have to ask how many bathrooms the house has - and
whether they have vents to the roof. Let's add the flues for the water
heater and the furnace. Is there a vent fan in the kitchen? How about

It could all add up to enough to pass about that much air.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by nicksanspam on December 22, 2007, 7:11 pm

Wind and temperature matter. CFM = 16.6Avsqrt(HdT), where A is the area
in ft^2 of 2 vents with an H' vertical separation and dT (F) is the indoor/
outdoor temp diff. Barometric pressures quickly equalize, but airflow in
a 50 Pa blower door test is about 20X the natural airflow.

Will your house float? Air also leaks around basement pipe holes and rim
joists and electrical outlets with walls opening into attics, dryer outlets,
fireplace dampers, baseboards and trim around windows and doors, and so on.

Usually from bottom to top in wintertime.

There is something called an "equivalent leakage area." I'm not sure how
that's calculated, but if your house has a A ft^2 of holes at the top and
bottom with an 8' height diff and a 40 F temp diff, 83 = 16.6Asqrt(8x40)
makes A = 0.28 ft^2, ie 40 in^2, eg a 6"x6" hole, or 2 4"x5" holes, or
a 40" crack 1" wide, or an 80" crack 1/2" wide, or...


Posted by Jeff on December 22, 2007, 8:10 pm
 nicksanspam@ece.villanova.edu wrote:

   Is that the square root of Av or the square root of HdT?

   OK. Here is what I'm thinking:

   The blower door test doesn't give a direct relation to heat loss  due
to the infiltration. It gives an indication of the size of the leaks
though. Where they are matters.

  It seems that the most important leaks are those in the ceiling and
those in the floor.

  In my house (1920), I've blown cellulose in both the walls and the
attic (gable vents). I would think that would take car of much of the
ceiling leakage. Years ago, I sealed the sills from outside and I
believe the cellulose has filled in above the sills. It's behind the few
outlets my house has.  I've caulked some around the floor boards.

  It seems to me that I need to attack the plumbing. Do I need to
revisit the sill and attic?


Posted by nicksanspam on December 23, 2007, 7:02 am

The square root of (HdT), as in the example below.

Sure. You might consider a blower door test.

Posted by Jeff on December 23, 2007, 3:55 pm
 nicksanspam@ece.villanova.edu wrote:

   I just wanted to say thanks. To yourself, and Gary, Morris, Solar
Mike and all the rest here.

   Have a good XMAS.


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