Blower door test and air sealing for HVAC sizing
Hi all. I have a question about a chicken/egg problem for our HVAC planning, air sealing and blower door testing. We purchased a newly built home that is mostly finished but has a lot of outstanding work for mechanicals. The wall assemblies are a roughly R55, modified Larsen truss system sitting on a walkout basement of ICF with 8.5″ of foam. The house was originally constructed for another contract which fell through so we didn’t have any involvement in the planning process. The visible air sealing details look good (the attic entry port is very well taped) but the builder never performed any intermediate blower door tests prior to drywall. The basement is still unfinished and the window and door rough openings have been sealed with spray foam but not yet taped. We’ll be finishing the basement prior to moving in. We still have several penetrations that need to be made in the envelope. In the ICF this will be
– The ERV inlet and outlet
– An internet wiring connection
– An intake for a backup direct vent propane heater
– Wiring for the heatpump compressor
– Lineset for the basement ductless minisplit
– 2 hose bibs
I’m sure there are likely more but that is what I am currently planning for. There will also be lineset penetrations for the first and second floor minisplits.
My question is which order is best for doing things. We’re in Canada so they don’t use a Manual J but I assume the HVAC contractor will use some type of energy audit for sizing and that this would be affected by results of the blower door test (we are hoping for around 1 ACH 50 but it is tough to know where the envelope is at at the moment). Is it possible to make all the penetrations (including the linesets and the compressor power) before we have spec’d out the HVAC equipment so that we can get more accurate blower door numbers and do any necessary spot sealing?
As a side note, the house has an Upnor radiant floor system installed in the basement slab and the first floor so the HVAC would only be for cooling and supplemental heating on the second floor.
I’d also be interested to hear how the process of doing load calculations has gone for other folks in Canada and what software most HVAC companies here use if they are not doing a Manual J.
Cheers
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Replies
Usually the person doing the Manual J puts in "average" for air tightness and that's the end of it.
If you've already laid the tubing for floor heat that bridge has been crossed. Although in a tight house like yours I would recommend sizing the floor heat for only a small portion of the heating load and make up the rest with forced air. That way you can have it on full almost all winter and get that cozy floor feeling all the time.