New struggles with new-to-me Vermont Castings Encore 2550

[Squatcher]

While tight, the house is funky. It was originally built as a giant shop/garage with an apartment in a loft at one end, and gradually all of the shop was converted to living space - some more elegantly than others, depending on the owner at the time. The underlying construction is concrete block covered with cedar siding on the outside and drywall and insulation on the inside. The attic has the max brand new blown in insulation - not sure how deep but its like snowdrifts up there. I did spend a fair amount of time in the attic when the insulation was out and didn't see any gaps or logical leak spots, but I suppose it is possible.

I say the house is tight because it holds heat forever overnight and the gigantic furnace in the attic creates suction on some of the doors when it runs. Its like I can hear the house pressurize when it kicks on. Note that I never run the furnace when operating the wood stove, except occasionally for a few minutes just before bed to warm up the rest of the house (stove is in the central great room so doesn't have much effect on the bedrooms). By that time I'm no longer dinking with the fire anyway. Its possible I don't really need to crack a window when lighting, but one time early on as I was getting used to the stove last year I got a back draft and smoke, which in retrospect I think was more of a weather fluke, but just to be sure I crack a window now. When I open the window I always feel cold air rush right in.

Its warmer this evening so I imagine I will have no problems at all, but will investigate a bit further and educate myself on the stack effect and look for drafts from the attic. Thanks very much for the suggestions!

 

[Diabel]

I say the house is tight because it holds heat forever overnight and the gigantic furnace in the attic creates suction on some of the doors when it runs. Its like I can hear the house pressurize when it kicks on.

This ^^^^^ I do not understand. I have not followed this thread closely, but what you say above makes no sense to me. I might be missing something….unbalance comes to mind

 

[begreen]

Yes, it could be a good clue. Particularly if there is inadvertent air leakage through the hvac system. The fact that is in the attic makes it suspect.
Squatcher, does the furnace have a fresh air makeup intake?

This ^^^^^ I do not understand. I have not followed this thread closely, but what you say above makes no sense to me. I might be missing something….unbalance comes to mind

Yes, one should not feel a pressure difference when the hvac blower comes on. That is another possibility, particularly if the return is in one section that is somewhat or completely closed off from the other when a door is closed between them. That can definitely cause a pressure differential, which should not happen in a properly designed system, but I have seen it in add-on situations like this.

 

[stoveliker]

The pressure tightness of ducts generally sucks (unless covered in spray foam).
Having that in your attic is a giant leak.

Also doors being pulled suggests to me that your fan is too strong. Creating more problems (because pressure differentials are larger).

Also, not seeing leaks doesn't say anything. Did you see the too plates of all internal AND external walls sealed? Air goes in an electric outlet, migrates up, and gets in the attic right in the 1/20" wide (but many feet long) gap next to the top plate.

Those need to be sealed. All.
All fixtures too.

I spent 6 weeks evenings and weekends in the attic doing that (pulling up bats, sealing, putting bats back, and adding R38 to the older R19.
That killed the stack effect in my home.