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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Does the house have air conditioning?  

What type of furnace - what draft type?

Does the water heater have a spill switch or some type of safety in the event of backdrafting?

A guy in Syracuse was killed by a whole house fan a few years ago.  If I recall correctly, hot day turned to cool evening and his furnace kicked on.  He forgot to turn the fan off, it backdrafted his furnace and he died of CO poisoning.  

People seem to think these things save college tuition payments.   It's very likely the wintertime loss through that huge high in stack hole costs WAY more that the few sheckles it saves on A/C - if it even saves (definitely can cause higher latent load due to operator ignorance). 

Central AC.

A high-efficiency (sealed combustion) gas furnace, and an natural draft gas boiler.

Quite frankly the DHW unit should be replaced asap. There is not a single safety feature on the unit to speak of.

Damn shame about the guy in Syracuse. That story and all the input thus far really drives home the point of combustion safety for me.

At this point my goal will be to convince the HOs to replace the existing DHW unit with an indirect tank, and hope they will go for a high-efficiency gas boiler. Next I will try to convince them to replace the existing FG batt insulation in the rafters with either 3-4" closed cell foam, or a flash and batt approach, or a rigid and cellulose cavity fill approach. Then we can discuss an upgrade to a smaller, more efficient fan.

Any issues y'all have with this thinking on my part?

If they have AC, what is the point of the fan?  Do they think it saves them energy?!  Do they realize how incredibly efficient properly designed AC is these days?  Ask how much they "think" the attic fan saves them!     

How silly does it sound to take a towel out of the dryer only to throw it in the pool?  

People with attic fans remove ton's of latent all day, then throw open windows and suck it back in at night.  Furnishings absorb the moisture and become uncomfortable.  Houses become clammy, and moldy.  Dehumidifiers in basements run continuously attempting to dehumidify the great outdoors.  It's completely absurd.  

Fix the house, teach them to use the AC, and let them see the fan was costing them energy, comfort, and IAQ.  Attic fans have absolutely no place in a home with AC, they work at cross purposes.  

Thanks Ted.

I have begun the process of convincing the HOs of completely re-thinking the systems currently in operation for their house.

We'll see where this goes.


Show the HO the total house and CAZ depressurization with all exhaust fans running and just the whole house fan running.  You may be back-drafting the DHW now.  Use the blower door to pressurize the house back up to zero Pascals.  Cruise control works good for this application. The CFM through the fan is very close to the total CFM exhaust of all the fans, or the whole house fan if that is all that is running. 

Once you know the total exhaust fan CFM, you can calculate what the house depressurization will be after air-sealing to the BAS. Use dP = 50*((CFMfan/CFM50)^(1.54)) to calculate the predicted depressurization.  As an example, if your exhaust fans total 400 CFM, your house depressurization will go from -1 Pa. to -2.3 Pa. when you tighten the house to 3000 CFM50 from 5000.

A Heat Pump Water Heater (HPWH) may be the way to go to eliminate the risk of backdrafting a water heater. HPWHs are worth checking out.

Thanks Dale, great advice.

Also, in regard to the HPWHs, I have pushed a few before but have yet to have any bites. I will def continue the push for HPWHs.




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