While obtaining a rough cost on a mini-split installation for my shop I asked a couple of local contractors what a similar capacity central HVAC system would cost. I was surprised to learn that the latter without ductwork would be about the same and possibly a little cheaper. Then I thought why not place the central air handler on the portion of a recently constructed mezzanine where the the slope of the roof makes the area almost useless. The intake could be provided with necessary filters with little ductwork and exhaust into the open space of the shop, again with little ductwork. The compressor unit would be immediately outside along the same exterior wall. See pic below. The advantages that I can see with this setup as opposed to a mini-split is 1) a propane furnace could be used instead of the heat pump, which will probably heat up the space faster. 2) better air filtration 3) used systems are readily available at a fraction of the cost. I'm not too concerned about the not so ideal efficiency of a used system. I would only use the system for heating and cooling a few weeks out of the year. Most of the time it's quite comfortable in the shop with our southwest climate. And yes, before it's mentioned, I need to address the lack of insulation.
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