I have been able to reduce the leakage rate of a challenging house built in the 1920s.

Still, the homeowners are adamant about wanting to address a couple of tough spots, and I need some help. The two spots are the mail slot in the front storm door and the attic fan.

The mail slot:

The attic fan:

So, the attic fan is the focus for now. Notice the door hardware on each side of the wood panel walls. The HOs still want to be able to access the closets with whatever solution is pursued. They do not want to remove the fan.

Originally, I was going to fabricate a panel of rigid foam insulation that would extend from the floor to the ceiling. I was going to make sure the rigid foam panel could be easily removed and replaced. 

Any thoughts on how to seal the attic fan and\or mail slot in the storm door?

Thanks in advance!


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It appears the mail slot in the wrought iron goes through the solid wood door? Can you post the interior portion of the mail slot?

Nothing constructive to add, but the idea of air sealing a home with an attic fan that large scares me.  Is it serving as a whole house fan or is there an intake area to supply air flow from just the attic?


Hello Bud.
It's something I would normally be concerned with as well, but this house is very leaky. 5,500 CFM50, with a BAS near 3,000. The majority of the leakage is concentrated in the basement and the attic. I concentrated all my efforts thus far on the basement (where there was also pest issues).
So, does a leaky house with a whole-house fan pose a problem with regard to safety? 
My sense is that all such questions can be eliminated with sealed combustion equipment, but, then again, what about gas ranges, ovens, etc?

First, the mail slot.  If the mail can drop into a pocket that has another sealed access from the inside, at least it would be air tight. 

The good news is that old homes can rarely get too tight, however, what size is that fan.  A BAS of 3000 would be a natural around 150cfm, if my thinking is correct.  And a fan that size could be 3 times that volume, driving the entire house negative.

I'm in north country and often hear the excuse that a whole house fan and a furnace don't need to run at the same time.  Well, they may not need to, but it could inadvertently happen.  A fan left on from a hot day and the stat picks up a call for heat and suddenly you have a house full of fumes or worse.  I always suggest an electrical interlock where the furnace or stat is locked out when the fan is running.  Applies to range hoods as well. 

You didn't mention where that fan is pulling its air from, the house, a window, or attic venting.

Is the hot water gas or oil?


The electrical interlock you speak of sounds promising (given the number of houses I have encountered with whole-house fans).

As for the size (capacity) of the fan I don't have that info handy.

The fan is pulling its air from leaks in the attic to the outside, as well as leaks between the attic and the rest of the house. As with most folks, they only run it in the summer (with a whole lot of windows open). 

The hot water is gas.

You raise an interesting idea thought about the pocket with sealed access. I need to think that one through a little.

Would it be possible to build a pair of bifold (closet) doors in front of the fan? I would install an interlock there as well so the fan can only run when the doors are open. Obviously, you will need to have a way to lock them open. This may not completely reduce leakage through the fan, but it should reduce it substantially. 

Do they have gas cooking appliances? 

They have a gas range\oven.

The bifold doors complete with an interlock sounds very promising...if I can reduce the leakage substantially then I'm happy, as I sure the HOs will be as well.

Thank you Bruce.

hey Patrick ...

I think the 1st thing I would do is to completely/ temporarily seal both the mail slot & whole house fan and do a blower door ... then do without sealing to see the implication ... if it is not all that significant, why worry ?

That is also a route I thought about taking Paul. It is my sense that the attic fan is worth sealing up, but it is the HOs prerogative that the mail slot be sealed (they say it is drafty in the foyer and front hallway during the winter).

I will post the results of BD testing for the attic fan and mail slot after I get the chance to put together a temporary seal for the fan (and maybe the mail slot).

Regarding the storm door-is it an older one? It appears to be steel with single pane glass. Is that so? Could the HO's impressions be as much about the door being a thermal bridge?


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