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What kind of heat for a tight, high-R, 1,100-sq.-ft. outbuilding?

Patrick Mccombe | Posted in Mechanicals on

Hello Folks,

I’m in the process of building a 24′ by 30′ combination artist’s space and workshop in a new post frame building. An 18′ x 24′ loft creates the second floor. There’s a lot of detail on the building here

The building has good windows, will have an R-40 roof , R-27 walls, and it already has R-10 below the concrete slab floor. The walls and ceilings are insulated with salvaged poly-iso board that I’m assigning an R-6. My wife and I could be described as OCD with regard to air-sealing. The building is in Southwest Conn.

We want a heating system that will heat the building quickly so we can lower the thermostat when the space in unoccupied. Given our envelope, I’ve think we need about 24,000 btu/hr on the coldest days of the year, although I haven’t done a Manual J calc. Instead I used one of those somewhat bogus online calculators.

I’m wondering how to heat the space.

I originally thought I’d install a conventional gas (converted to LP) hot-air furnace with exposed spiral duct-work for a kind of a “loft” look. I was thinking 80plus efficiency to keeps costs down and make future service easy and cheap. My guess for parts is about $1500 to $2000. Labor is me, so that’s not a dollar concern, but it would be many hours (40 maybe) of installation time. Nobody makes a small enough furnace so the unit would be over-sized (40K input, 32k output), but it would likely heat the space more evenly than other options I’m considering. I hear $5/gl. propane is not far off.

The second option is this:

A wall furnace with direct vent. They have units sized correctly and the install is much simpler.
I’m not sure it would distribute the heat evenly, however. With an electric blower and incidentals, the material cost for this option is about $1000. My guess is that it would take a day to install. This too would run on propane.

The final option is this:

A mini-split heat pump, but maybe not this one, as it needs to be big enough for the space and work with my New England climate. The install is also easy and I’d get AC in the summer. My guess is $2000 or more for this option. We have among the highest electric rates in the country at .22/kwh.

Budget, both upfront and operating costs are the biggest factors here, so what would you do?

Your help is greatly appreciated.


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  1. GBA Editor
    Martin Holladay | | #1

    You forgot to tell us how you will use the space.

    Will you use it for 10 days a year or 365 days a year? Will anyone live there?

  2. GBA Editor
    Patrick Mccombe | | #2

    I knew I'd forget something. It's a work space for art and other handy pursuits, so figure on 30 plus hours a week of occupancy. Nobody will live there, but the loft may become guest quarters in the future.

  3. GBA Editor
    Martin Holladay | | #3

    OK -- it will be occupied about 18% of the time. Not much.

    I think you are overthinking this. Any of the options will work.

    I would choose either the propane-fired through-the-wall-vented space heater, or the ductless minisplit.

    Don't worry about distribution -- everything will warm up in an hour.

  4. gusfhb | | #4

    I think a minisplit will run more cheaply than propane, and you will get ac for free. AFAIK only the small ones will do the low temp operation, so you may need two if your calc are correct. But how often are you going to use it at design temp? You could start with one and supplement with regular electric.

    there is something about a woodstove that no matter how cold the room you can always get warm........

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