Replies

1. 
   PBP1 | Apr 07, 2022 07:59pm | #1

   Quite an amazing build, double my R values in Zone 6 (2100+sq ft), which is heated with a single 28.6 kBTU/h rated heat pump and three ducted air handlers (hence reduced efficiency compared to one-to-one and non-ducted).

   4 ton combined does seem quite high. However, your plans show some "future" spaces (to be conditioned?) and the sq ft does not appear to include the unfinished basement (another future conditioned space?). Would future spaces add another 1,000+ sq ft?

   With R-23 continuous exterior, I guess plumbing on exterior walls is no problem (e.g., mud room). And, the (future?) stairs in the garage, will they eat into one bay?

1. 
   Malcolm_Taylor | Apr 07, 2022 08:28pm | #2

   PBP1,

   Mudroom plumbing can go in wall between it and the kitchen. Waterlines through the floor of the cabinets, and if necessary an air admittance value under the kitchen sink = no plumbing in the exterior walls.

1. 
   PBP1 | Apr 07, 2022 08:38pm | #3

   Thanks, I've got floating vanities on my mind ;-)

2. Expert Member
   Akos | Apr 07, 2022 08:47pm | #4

   This is a great resource for cold climate heat pumps:
   https://ashp.neep.org/#!/product_list/

   Always best to confirm with the engineering data from the manufacturer as sometimes the data is off a bit.

   Installing a 5 ton system where a 2.5 ton was speced makes no sense. There is a turndown but that is still limited. With heat pumps it even makes sense to slightly undersize and make up for the those polar vortex days with a backup strip heater.

   The equipment cost more, ducting is bigger, louder units, run into cycling issues during the shoulder seasons and humidity removal.

   Install the equipment that was designed for your place, you'll be happier and so will your wallet. People are not used to high efficiency buildings thus the silly sizing they are suggesting.

3. 
   ktim | Apr 10, 2022 07:56pm | #5

   I have been trying to find a supplier north of you for our build. I get the same response everywhere, 'you need a 4 ton unit'. No calculations. No questions about construction (we are double wall). Just their '30 years of experience'. I also had one supplier spec a 12k head for a 509 sq ft apartment!

   Ignore the supplier and trust the designer that actually did the calculations.

4. 
   jaccen | May 23, 2022 07:12pm | #6

   Thanks for all the replies.

   @PBP1
   Thanks. We do have some plumbing in the exterior wall (kitchen sink and mudroom sink). We did try to minimize exterior plumbing, but we were also bound by the amount our plumbers would "bend" in regards to their standard practice. The continuous exterior insulation does alleviate many of the usual 2x6 wall concerns. The future space, if ever installed, would have its own ductless mini-split. The stairs would slightly eat into one bay; however, we have a minivan for the "whole fam" and a small hatchback as a commuter that will easily fit underneath it. We always try and get away with the smallest vehicles possible for a number of reasons I won't bore everybody with.

   @Akos
   Thanks. That was my thought on the matter, but it always is better to hear someone else rationalize it back to you.

   @KTim
   Agreed. It has been *extremely* difficult sourcing subs/suppliers. We spent all the time and effort to get the plans and calcs right (and, quite frankly, we needed more time as we were learning as we went). Unfortunately, all of our replies seem to be "well, we've always done it this way." Which is disappointing because it seems like much of "always done it this way" is not.........being diplomatic.........right.