New Tight House – Negative Pressure – Wood Stove Causing Issues – Make up Air issue? – GreenBuildingAdvisor

Hello!

Just recently finished and moved into our new Construction house.  First (and last) house I built and designed myself with zero prior experience.

Western MA, Zone 6.  3 indoor mini split units, and a brand new Vermont Castings 2040 CAT wood stove, with  fresh air intake system installed.  The stove pipe is a straight shot up, no bends.  Is single wall where pipe is exposed on the 1st floor and insulated pipe through 2nd floor chase, attic and up through the roof.

House is 32′ x 24′ with two floors and a basement.  8′ ceilings on 1st floor, 2nd floor has 6′ walls at eaves side, sloping up to 8′ ceilings.  the basement ceiling is approx 6′ 6″ in one half and about 4′ 6″ in other half – an “almost crawlspace”.  Vented attic, 10/12 pitch

The basement is insulated on the walls with 3 inches of foam, and is therefore considered conditioned space.  

*Important Information*

We thoroughly sealed off the wood stove flue, the fresh air intake system, and the stove pipe seems before our blower door test. (the insulated stove pipe seems that are buried in wall chase are permanently sealed). Having no experience, I was scared I would fail my blower door if I didn’t do this, which apparently is common practice…(?)

*Blower door Results as followed

*Total conditioned space = 2,336 sqft

*House Tightness = 263.2 cfm50 (0.86 ACH50)

*x2 Continuous Bath vents were to set by HERS rater to 35cfm and one at 40cfm.  Both have boost options on a timer which are used for shower, etc.  

*Kitchen hood vent above our induction range which maxes out at 400cfm – I chose this model under the impression that I would not need make up air.  

**Issues**

I’ll start by noting that the fresh air intake for the wood stove, BY DESIGN, is not connected in an air tight manner to the firebox.  Something I only now am noticing, as I didn’t install the wood stove system.  The fresh air intake is screwed in place behind the firebox’s air control flap, with a box surround that has plenty of air space for air to leak in or out.  The fresh air duct goes down into basement, where the duct insulated, turns 90degrees and heads out the south west side wall.

* When the woodstove is cold – With 30cfm of bath vent exhaust turned on, no air is pulled into the house through the stove pipe seems, but air does come in from fresh air intake.  At 60cfm of bath vent exhaust, cold air is pulled through stove pipe seems into the house and noticeable more cold air is pulled in from fresh air intake leak.  When no bathroom vents are running, there is still cold air leaking in from the fresh air intake, but at a lower rate, and the stove pipe seems no longer leak inwards. Once a fire is established in the stove, smoke/co2/air is able to resist being pulled into the house by the bathroom vents (though I haven’t experimented with running both of them at specific cfm to see where the threshold is)  But I’m guessing its safe to assume that at certain point as the fire slows down, it will begin to slowly leak into the house if even a single bath vent is turned on. *Needless to say, when the kitchen hood vent is used in conjunction with or without the bathroom exhaust vents, it can pull plenty of smoke into the house, within seconds, even with a well established fire going.  (cracking a window when using the kitchen hood is an easy enough of a habit to get into – but is not an elegant solution and doesn’t solve the other issues). 

 The potential for a slow leak of smoke/cO2 as the fire dies out is my main cause for concern.  As well as the pulling in of cold air when the wood stove is cold and any exhaust is. being used.  It’s my understanding that having continuous exhaust via bathroom vents is important for air quality/air exchanges, but the exhaust vents are pulling in cold air and likely smoke/cO2 at low firebox temps.  

  Does anyone have any reasonable solutions/insight.   I can’t bare to rip open walls and run ductwork. This business of balancing variable air pressure scenarios is over my head and I’m not sure how to proceed in finding an inexpensive solution.  We were originally quoted 10,000$ for an intelli-balance ERV which we could not and still cannot afford.  

 Ive attached photos of the spots where there are noticeable leaks.  Thank you all very much in advance!  – MD