Hi,

I’m building a a new, fully custom house in central NC, technically climate zone 4, but we are about 15 miles from the climate zone 3 border.  2365 sq ft on first fooor, ~980 sq ft finished on second after some minor alterations during framing, with another 625 or so unfinished on second floor, about 60% of which is a bonus room above the garage I expect we will finish in the first year of living there.  Basement is unfinished and sealed off and not important for this discussion other than to note it is Superior Walls and about r25 rated walls with all the rigid insulation in the wall assembly.  If we ever finish it in the future, it will have its own HVAC systems separate from the rest of the house…

This house is my best attempt to be air tight and super insulated with a semi standard builder, since someone who does elaborate building envelopes is very rare in these parts, and definitely not available in the neighborhood we chose to build.

My Builder does energy star level efficiency and air sealing and does bring in a team to caulk and air seal as part of that.  He is letting me hire a second crew to come in behind his guys and go further on the air sealing with a second blower door with smokers to further seal…  I want to get to a minimum of 1ACH50, and preferably as low as I can with good, simple materials and just care and effort to seal as best we can.

The house itself is framed as double 2×4 wall construction with air gap between the framed walls and 1” rigid insulation on the outside.  Dense pack cellulose insulation.  9+ inch total thickness wall assembly.  Rim joist areas in the truss areas between floors is air sealed and insulated to the same levels as the wall assemblies.  Vented attic, but we are doing everything we can to seal the Sheetrock lid between conditioned space below and the attic.  Raised heel roof trusses and blown in cellulose to min r48, above r60 where it will fit.  Zola passive house rated triple pane tilt and turn windows and patio doors imported from Europe.

My frustration has been in trying to figure out the best HVAC setup that makes sense economically and finding an HVAC contractor that is experienced enough to design and implement something other than standard ducted forced air heat pump setup or even put in a high efficiency version of ducted heat pump for a reasonable price.

I should have been more forceful trying to get good advice and finding a high efficiency HVAC vendor.  But I’ve just not had any real luck and now I feel backed into a corner without good choices…

the builders preferred hvac vendor finally got me some quotes and did do a version of a manual j that I think sort of almost captures all the unique things my house does that none of the other typical builds around here have.  They calculate that peak load is about 3.3 tons for the finished square footage of the house (a little over 2 tons for first floor and about 1.2 tons for the finished spaces upstairs, but a little over 1.5-1.7 if I want to size it to cover for the unfinished bonus room when I finish it later after closing) given the amount of two story open spaces, the southern orientation of the house and the amount of glass I have in the house (a lot), even with the air tightness and level of insulation in the walls and windows.

they are pretty much solely an American Standard shop, but do carry Mitsubishi (although I get the impression they do very little of it and certainly not whole houses with it).  The builder’s standard, included in the sales contract, HVAC package for my house is an A/S Silver 14 SEER single stage setup for each floor.

i got a baseline quote for the builder standard setup (to know how much extra we would have to pay to do anything different), a zoned 4 ton (since they don’t do half ton sizes) single compressor/air handler setup to do both floors Platinum 20 “variable speed” 20 SEER system, and a Mitsubishi multi zone system that used a single 4 ton multi head outside compressor and 2 of their ducted air handler units (i asked for PVA, but they quoted me MVZ series).

Our previous house was a little bit smaller square footage but definitely nowhere near as air tight or as well insulated as this new house will be.  Looking at the last 10 years worth of power and gas bill history for that house, we averaged less than $200 per month in utility bills for power and gas for the entire house.  I know the HVAC won’t have to work nearly as hard in this new house’s building envelope.  So I expect our bills would be, on average, less than before even using the builders standard HVAC setup…  I’m expecting maybe 160-180 a month or less on average in the new house…….so even if a platinum 20 setup was to magically cut our new utility bills in half compared to using the builders standard setup, we might be talking 80 a month savings…  and it is highly unlikely to save that much on its own…  but absolute best possible case scenario in a totally ideal world, it might save around a thousand a year to go super high efficiency with the HVAC…  given the typical lifecycle of compressors outside in NC heat, if you get 8-10 years you are very lucky, anything more than that is just waiting for the failure and I bet it’s nowhere near it’s original ratings…

to commission the entire setup including putting everything in from scratch including ductwork, etc, it’s 10k for the standard 14SEER, 18k for a single compressor/air handler zoned 4 ton Platinum 20, and 24k for the Mitsubishi setup.  Yes, I can buy the Mitsubishi equipment online from various online vendors for half the difference in price these guys want to go up to Mitsubishi from 14SEER (forgetting the first 10k price of the 14SEER system install itself)…  I could have them put in the 14 seer and put in the ductwork, move in the house, rip out the brand new equipment and pay my HVAC buddy to help me put in the Mitsubishi stuff and still have a bunch of money in my pocket, not to mention having brand new barely used A/S 14SEER equipment to sell and recoup some more…  I just don’t understand the difference in price….  it seems out of whack if not bordering on gouging…  is this typical for others to see this kind of price differential?  One platinum 20 air handler and platinum 20 compressor is almost double the price of 2 14 SEER compressors and air handlers?  It can’t be labor…  it’s half the equipment to install in the case of the platinum 20 setup 🙂

But looking at it another way….. if I could cut my old utility bills in half  and save $80 a month in utility bills switching to the more efficient platinum 20 variable speed unit or the Mitsubishi units, it still wouldn’t really pay itself back over the typical 8-10 years a system lasts here in NC…

Am I missing something in the equation here?  Should I keep shopping for a better deal?  Should I be looking at using a different kind of equipment setup for the house and can save cost on the equipment that way by doing a few ductless heads instead of these ducted heat pumps?  Or should I say screw it and just live with the standard setup because the difference in price will mean the higher efficiency stuff will just never pay for itself and worry about replacements down the line and put in Mitsubishi I buy online in 8-10 years?

Part of my frustration is that the more efficient equipment seems wildly overpriced in my quotes.  I would like to get the noise reduction a variable speed setup would bring and not have that stupid dump that happens when a single stage setup kicks on and have to listen to it run full blast pushing air at max power….  i would like the more calm, only running as much as it needs and dehumidifying as it runs nonstop that a variable speed or full variable refrigerant flow setup offers…  but the math just seems to not make sense to me….

thoughts?  Thanks for making it through my rambling 🙂