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2-stage/2-zone vs 1-stage/1-zone & foam vs fiberglass ?

5 years ago
last modified: 5 years ago

Rather than have a large garage w/ a floor above it we are doing a small attached garage and then building a separate building with a garage and my photo/woodworking studio above. Original plan was spray foam insulation throughout. To save money our builder is suggesting fiberglass instead. HVAC guy had proposed a 2-stage/2-zone (for the main level entry/bath and upstairs studio & office/storage) but has also proposed a 1-stage/1-zone option to save money. Both also include a unit heater in the garage.

System is natural gas. $0.81/therm summer, $0.86/therm winter.

It will likely remain unused for 5-12 weeks in the cold (Minnesota) Jan-Mar period when we snowbird in warmer climes. Usage otherwise is somewhat hard to predict. There will be times that I'll be working in the office and so want it and the bathroom comfortable and not care about the temp in the studio & entry. Garage will have a unit heater but will rarely be used.

So, 3 inter-related questions:

1) Sprayed foam insulation is $17k, fiberglass (excerpt below) is $9k. Given my usage I'm not sure if the extra $8k is worth it. Foam would likely reduce drafts somewhat? And make it noticeably more comfortable?

2) 1-stage/1-zone HVAC is $18k. Would it be worth $4900 to go to a 2-zone/2-stage system so that I could heat just the office+bath? Any thoughts on likelihood of saving enough on heat/cool to pay for most or all of this? One other advantage of 2-stage would be better humidity control in summer though I'm not sure how much of a difference it will make in such a small building. 2-Zone might also allow for lower air flow and so less dust blown around (and less filter cleaning)?

3) The building will likely be kept about 45-50°f throughout our Minnesota winters though winterizing and leaving unheated Jan-Mar when we snowbird in warmer climes is an option. Besides winterizing the plumbing I'd need to move some photo gear that's not overly happy with freezing temps. This might best be determined after seeing what the energy usage is during first winter. Thoughts?

4) Other thoughts, ideas or suggestions?

My initial thoughts are that neither foam nor 2-stage/2-zone are worth the extra cost.


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