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Community and Q&A

Best heating/cooling for 3600 sq. ft. remodel in zone 5

Sara Pancake | Posted in General Questions on

I will apologies in advance for the many questions and future questions and thank you everyone for your help in advance.

We’re purchasing a 3600ish sqft house built in the late 70’s.
There is no ‘code’ here. I will ask about the the manual J however I do not expect that is going to happen.

Zone 5A
3600+sqft two story with full basement and a lot of windows
Current Heat: EBB, three propane ‘fireplaces’ that I  will assume are not functional
No access to natural gas, potential geothermal, could use propane

Goal: Best and most economical long term heating system. Mini splits are NOT widely used here.
My expectation is the electrical will need upgraded for this system- do the heating contractors routinely take care of arranging this or will I need to get an electrician as well?

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  1. Jon R | | #1

    I would use low temperature mini-splits. If you already have a well, then possibly geothermal.

  2. Expert Member
    Akos | | #2

    If you already have baseboards, your electrical is fine to go with mini splits, they use between two to three times less energy and power than baseboards.

    Since you already have a heat source, usually the best return is to add in a couple of hyper heat wall mount mini splits to take care of the bulk of the heating. With a larger house, you are probably looking at something at either end of the main floor with at least one near the staircase going up to the 2nd floor.

    This would take care of most of the heating, your existing baseboards can then provide the bit of supplemental heat for each room.

    The two units do need to be sized for the house, it is best to get someone other than an HVAC contractor to correctly size the units.

    The other option is to go with a fully ducted setup, but this is typically cost prohibitive for a retrofit unless you are doing major interior work.

  3. Matt F | | #3

    There will not be an existing available manual J. You should get an engineer to do a manual J, S and D (if doing any ducts). This info will be provided to the HVAC contractor.

    Air source mini splits are likely the best option. Both Mitsubishi and Fujitsu both have search tools to find contractors. Use your engineer plan and hold the contractor to it. If you have existing EBB, you may not need much electrical done, just service to the minisplits, which the HVAC installer can coordinate.

    Why don't you think the propane fireplaces work?

    Before tackling the heating system though, in a 70's house, I would have a blower door done and tackle any low hanging options for improving the envelope. Finish that work and see where you are at for a heating system.

  4. Sara Pancake | | #4

    Thanks- the propane fireplaces propane source may be compromised, the tank is gone and the lines look sketchy to my untrained eye. I will have that evaluated.

    Mini splits are almost never used in this area, if I ask for them is there any worry about the inexperience of the contractor?
    I've already had the answer of ' those J calculations are never right, they don't take into account that the insulation has sagged or for the air leaks around the house.' Which is better than the 'what?' that I expected.
    I will have the blower door done, I did actually find someone for that.


  5. Expert Member
    Dana Dorsett | | #5

    Those '-J calculations may never be right, but they have a far better track record that WAGs done by HVAC "professionals".

    If it turns out there are deficiencies in the air sealing and insulation it's worth it to fix them. That's even more so if geothermal is being contemplated. In my area it's cheaper to reduce the load by a ton (or even two) on a house that size & vintage than it is to install the bigger geothermal system to cover the higher loads of a leaky house.

    Describe the windows. Are they being replaced? Are there any storm windows?

    Are the foundation walls insulated?

    In most cases it's not worth reviving a propane fire place for space heating. The efficiency is pretty low, and the air tightness is usually low too. It's usually better to just get rid of them entirely, since they are usually more of a heat leak than a heat source.

    Until you get an aggressive Manual-J on the "after upgrades" condition of the house it's premature to start specifying the heating system. If you go through a heating season using the baseboards for heat you would be able to infer the whole-house load based on your wintertime power use. That may be worth it even if air sealing & insulation upgrades aren't yet complete, since it would establish something of an upper bound on the eventual load, and would allow you to directly measure progress. A primer on how to use energy use for inferring heating loads see this:

    Any contractor experienced with installing split-system AC or heat pumps can handle mini-splits. But don't trust any HVAC contractor to size it correctly ( that's what independent Manual-Js are for). AC installers also may not be clued in to issues such as snow depth or roof avalanche burial or falling icicle damage to the outdoor unit. Mounting the compressor with the pan above the historical high snowpack depth, protected by overhanging roofs (rakes are preferable eaves) goes a long way toward avoiding mid-winter problems. (I pass a couple of houses on my daily commute where they have to dig out the mini-split after every big nor'easter snowstorm- you never want to star in that movie.)

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