I live in northern Canada (I can see Alaska from here). My two-stage, 3 HP DC is vented outside.
When running the DC for a long time, there is a noticeable drop in temperature in the shop. My shop (1200 sq ft - 10' ceilings, floor raised 6" off the slab and insulated) is heated with a propane furnace. I also installed three small electric infrared heaters (the 1500W type you can get at any hardware store). I placed the heaters on the ceiling, pointing at my larger cast iron machines - this heats the machines, causing them to radiate heat whenever the IR heaters have been on for a while.
It works well. If I'm running the DC for hours at a time, the shop can get cool - but for normal 15 - 20 minute "bursts" throughout the day, the fluctuation is not enough to discomfort me. The IR heaters are hooked into the lighting circuit, so they're only on when I'm in the shop. The propane furnace is controlled by a thermostat - if I know that I'll be running the DC for more than 30 minutes or so, I'll shut it off rather than burning propane to no effect. The heated cast iron brings the temperature back up quickly after the DC is shut off.
It works for me - no guarantee that it'll be suitable for you.
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