Building looking east. On the north side is an open unenclosed shed. Overall height is 28'. Main is 8'6" ceiling height. Second is 16' to the highest point.

Main level plan (up is east, garage doors open to south). Building exterior is 42' x 25'.

Second Level.

You could look into AirBnB and rent it out during the times of the year you aren't using it. (You know like people who like snow activities) Then just spend the money on the best and never regret it.

HVAC is primarily for comfort, if you're not using it you could argue you are saving money because you are not using it, but you paid some money to be able to use it. It's half one, dozen of another.

So I don't know there is a good answer to what you are wanting to do.

Those prices are insane. Does he use gold-plated foam/fiberglass and AC components???

If you can achieve the same level of insulation with fiberglass then there is no justification in using spray foam. If the spray foam was able to produce an higher insulation value then I still don't think you should spend the extra $8K. You winter usage is low which results in very little savings in the winter. You are in a northern climate and won't have a high cooling bill. You likely will never see a return on the $8K investment. You can get a similar air infiltration performance with fiberglass if the builder knows how to install the proper air and moisture barrier.

Spending the extra $4900 is more about additional comfort. That is something you have to justify. Do you know the model numbers of the equipment for the two options? The single stage could be a low tier equipment, while the 2-stage could be variable speed with higher efficiency. You should compare the equipment to understand what you are getting if you spend an extra $4900.

Those prices are high.

When you pay that much for HVAC, it really makes sense to superinsulate and then just use electric baseboards. Even 1/2 of $17k would get the structure to a level where you could fully heat with electric baseboards for what you want for $100 a year. If you need a/c, do a minisplit for $4000 installed and that $100 goes to $30.

By superinsulate - sprayfoam is not it. In your climate, you want R40 walls which is achieved by 12 inch thick walls with cellulose/fiberglass or 3-4 inches of rigid foam on top of 2x4 wall. Sprayfoam has its place but filling a cavity with it is not what it is best for.

Are you really looking at R20 walls? Is that even code? Or is there rigid foam that you have also?

There are no drafts in a modern wall - fiberglass or not. $8k for sprayfoam is a waste. If it is 2 inches of rigid foam on the outside - then it is not.

My walls in NC are zip R3 over fiberglass bibs in 2x6. The small amount of rigid foam just helps with the thermal bridging of the framing. The bibs fill voids much better than batts. It is blown in. We have foam in small areas that bibs would not work with. I think $10k did our 3800 sqft house (not counting the zip R which was $3k upcharge over zip).

I would think you would want R-80 in the roof which is probably best achieved by rigid foam over the sheathing given the rafter space needed.

Or you could just do code minimum and minisplit with electric baseboard back up it since it isn't full time use.

Thanks all. Three people have said the system is too expensive. Can you give me some idea how too expensive it is? 20% more than it should be? 2x? 3x?

The extra $4900 for 2-zone should produce some energy savings if it allows me to heat/cool only the office & bathroom? Any idea how much? Or is the difference likely to be so little that it's a non-issue?

I agree that if we built to passive haus or similar standards we'd use a lot less energy. Unfortunately builders and architects in MN have been slow to embrace exterior foam. We actually started down that route on our main house but our architect became uncomfortable with the unfamiliar wall structures and said they wouldn't do it. If this were just me I'd have switched architects at that point but there is a lot more to building a house than just energy efficiency. I wish I'd pushed the point more and again with this structure but that's now water under the bridge. I got a lot of flack from them when I suggested just double stud walls for it and at some point you get worn down fighting your own architectural and building team and you just want to get your wife the house she's been wanting for the past 20 years. When it comes to aesthetics they are excellent but they have little to no understanding of anything mechanical (including what problems their designs cause).

Thanks,

The quote of $18K for single stage HVAC may be on the high side, but then again you haven't stated what is included in that quote. The structure is 2100 sq. feet. Does this quote include all duct work and wiring? Do you have the model numbers of all equipment?

The additional $4900 for the 2-stage and two zone is not that unreasonable. What equipment would you get for that additional money?

I do not yet have detailed info. The system does include all ducting. What I know so far.

I believe the conditioned portion (not including the garage) is about 1400 sq ft.

Thanks,

So you have an architect in MN that isn't comfortable with foam or thick walls? I wonder why they are so behind? Midwestern stubborness.

I did my last house at 2100 sqft with 2 Trane systems, seer 15 with a 10 year parts and labor for $13k. There is 18 registers throughout the 5 bedrooms, and 3 retruns. 2 stories. My current build is 3800 sqft with $15k for very similar setup (AS, seer 15, single stage) with a few extras. Each bedroom with separate returns. Includes duct work. So your 1 system for a higher price seems like double what it should be. Our inspectors are pretty tough and it includes ES duct leakage standards.

It would be fairly easy to have an architect find an engineer who could spec out a thick wall. But I understand all locales work differently.

I could see $18k put into solar panels and still heat with a minisplit and electric baseboards. Just a thought.