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I have built a workshop addition to my garage and both will be insulated. I'm located in Central Indiana, so we get chilly winters (often down to 0°F) and hot, muggy summers (90°F and 80+% humidity).

My goal is to keep them heated to at least 55-60°F in the winter to keep paint/glue/etc. within storage temperature ranges and to provide comfortable sweatshirt weather for working through the winter. In the summer, I'd like to keep it cool enough and, most importantly, dry enough to work without turning into a puddle of sweat. i.e. I'm not conditioning the space for year-round comfort, but to simply make it more livable.

My initial plan was to install a mini-split heat/AC unit, however my HVAC guy suggested a PTAC (Package Terminal Air Conditioner).

Some of my initial thoughts:

  • I've still got bare studs inside and no siding outside, so I can make whatever holes are necessary for either installation with minimum issue. Also, I've got a huge new panel with plenty of spaces (and plenty of headroom in my new 200A service), so power supply isn't a concern.
  • The PTAC units I'm familiar with (from hotel rooms) have all the controls on the top of the unit, so it would have to be mounted low. If this is true for all units, this would be inconvenient for this space, as I'm using it as a wood shop and it will take up room that tools, workbenches, other storage could use.
  • Mini-splits that I've seen seem to have the indoor heads up high which would be ideal to keep it out of the way.
  • The PTACs I've been looking at (shopping online) seem to have resistive heat and heat pump AC. That's definitely cheap to install, but expensive long-term. Am I simply missing the actual heat pump PTACs that use resistive heat only for backup?
  • Mini-splits require line-sets with coolant. AIUI, some come with the lines all pre-installed & pre-filled so I don't need to call anyone out to purge the system & fill it with refrigerant, but those systems are probably more than the ones that aren't pre-filled. I'd presume that it comes out close to a wash, cost-wise, in the end. (Especially since our HVAC guy is family and we usually get a reasonable discount.)
  • Ideally, I'd like to be able to monitor/control the unit with some sort of smart thermostat system. Again, all the PTAC units I'm familiar with have their own built-in thermostats controlled from the unit itself, so this may not be possible.

What things should I consider when deciding between the two?

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    The 0F might be the determining factor. Will need a mini split/heat pump that works below 0F or need alternative heat source. Using a toaster is usually not best for pocket book/wallet.
    – crip659
    Oct 22, 2023 at 15:28
  • Good points, @crip659, thanks. I've got a plumbed in NG heater in the garage, but I just don't think it'll do for the entire 1000 SF area of the garage & shop.
    – FreeMan
    Oct 22, 2023 at 15:32
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    Extra insulation never hurts if the walls are open still. Increasing wall space for more inches of insulation might hurt floor space. Wonder if there is a study of the costs of doubling studs for more insulation saves enough in the cost of heating.
    – crip659
    Oct 22, 2023 at 15:49
  • @crip659 Adding a thermal break would help, Zip insulated sheathing could be used or a rigid foam inside and probably wouldn't hurt floor space too much.
    – matt.
    Oct 22, 2023 at 15:53
  • "The PTAC units I'm familiar with (from hotel rooms) have all the controls on the top of the unit" They either come with integral controls or you can order them with no controls and contacts for a conventional wall thermostat. The latter is used in hotels where the thermostat has an IR occupancy sensor or is hooked into the property management system so that the temperature is set back when the room is unoccupied or unrented.
    – user71659
    Oct 23, 2023 at 1:07

2 Answers 2

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For a relatively small, single room installation, with full access to install anything, which is what this sounds like, I really only see two significant considerations:

  • Heating Type

Resistive heat is bad for new installations. Not so bad for occasional heat, but since you need heat running 24/7 in the winter, a heat pump is the way to go for any new installation. Check the equipment carefully before buying. It is cheap and easy to throw electric resistance heat into almost anything, and sometimes the way you find out (unless you can get a schematic) is by looking at power usage. If the heating BTUs ~= 3,412 x maximum heating electricity in kW then it is resistance heat. But it is also possible to have a unit where it includes heat pump heat and resistance backup. So look through the specs carefully and ask the manufacturer if you aren't sure.

  • Blower location

Most mini-splits I've seen have the indoor unit mounted high on the wall. That is, generally speaking, preferred for A/C, less optimal for heating. On the other hand, most PTACs I've seen are mounted low on the wall (and I don't think they can be mounted high on the wall), which is preferred for heating and less optimal for A/C. But overall probably not that big a deal one way or the other since you need heating and air conditioning in roughly equal amounts. (As opposed to Florida almost all air conditioning, for example.)

However, space usage is another story. A mini-split mounted 6' up allows you to make full use of the space below it for workspace or storage (shelves or cabinet). That effectively means the use of a few more feet of your room compared to a PTAC. PTACs installed in a hotel don't have this issue - they are often mounted below a large window, so the wall space, by design, isn't usable for anything else anyway.

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  • Thanks! This confirms some of my thoughts.
    – FreeMan
    Oct 22, 2023 at 15:33
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PTACs leak (air, that is)

The biggest issue with PTAC-class units (and TTW/window ACs as well, save for a few "U-shaped" window units that don't have this problem) is that they leak air like a sieve. This is not as big a deal in a garage, but for applications where you're trying to control airflow through the envelope, it's more or less a deal-killer.

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  • Hmmm... hadn't thought of that. Is that between the installed unit and the sleeve, or through the unit itself?
    – FreeMan
    Oct 23, 2023 at 12:06
  • @FreeMan -- generally through the unit itself Oct 24, 2023 at 2:48
  • Gotcha. Thanks. Nothing like the joy of the cold, Northwesterly breeze blowing though the thing that's supposed to be bringing me heat!
    – FreeMan
    Oct 24, 2023 at 11:49

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