Zone 6 HVAC – What am I missing?
We have been exploring HVAC options for our ND home in climate zone 6. Our original plan was air source heat pumps for primary heating and cooling. Fully dedicated ERV system (Broan AI or Zehender).
Radiant floor heat as back up. (I’ve installed a few of these systems previously and feel comfortable taking this on)
The Issue – The 3 HVAC subcontractors we’ve met with say our plan won’t “move enough air” and want us to just do a high efficiency gas furnace.
What am I missing? I feel like I read about many of you on here not having a dedicated air handler or furnace.
I will say we have pretty dang cheap gas and electric where we are at.
House Specs:
Ranch style – 3450 sq ft
ICF walls – Footer to top plate
Cascadia triple glazed windows and doors
R20 under the basement and main level slab
R60 blow in attic – Intello on ceiling
Aiming for sub 1 ach 50 on air tightness
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
You are not missing anything. There is no such thing as move enough air. If you look at the HVAC design process, airflow is an output from heat loss and equipment selection, it is not an input for anything except for sizing ducts and registers. There is no minum airflow a house needs.
The issue most likely is the HVAC folks are not used high efficiency structure with low loads so seeing a roughly 2 to 2.5 ton heat pump for 3500sqft feels wrong.
As long as the equipment you select delivers enough BTUs to maintain temperature it has enough airflow.
BTW, for new build I would go for ducted air source heat pump, not wallmounts. You are already planning ducts for the ERV, using the same ducts for heat/cool maybe upsizes them by an inch or two. Hard to justify the extra cost.
Same with backup radiant heat. I would install radiant only where you want the warm toes (entrance mudroom, kitchen and bath), these can be resistance matt.
In the land of cheap gas it feels like it it would be hard to go fully electric, but if you look at the cost delta including gas meter fees, you are at maybe $50 per year in savings. The extra cost of running the gas pipes and installing CO2 detectors plus redundant equipment means the ROI on gas is pretty much never.
Thanks for this response! At this point should I look to hire someone like Energy Vanguard to do a professional design as it doesn't appear ill get it locally?
Isn't using the same ductwork for an ERV frowned upon?
Deleted
They’re speaking gibberish. I think the whole
house ducted heat pump system is an easy call. Overall heating costs will be low with that level of insulation, so avoiding gas “service” fees makes a lot of sense. But it’s a small amount of the cost of a custom house so don’t sweat it too much.
Ask them to show you their Manual J calculations. On a current project I had a mechanical engineer design the HVAC for a high-performance home. The HVAC contractor questioned the sizing of one of the units and shared their Manual J outputs (not the inputs) which gave a system almost three times what my engineer had come up with. Of course the contractor's inputs were appropriate for an average house built in the 1970s, not a high-performance home built in 2023.