Side of the house. Though it will fit under the deck, it is likely to work harder if the heat does not dissipate completely.

 

I would like it under the deck if you're in a snowy climate it will keep the unit from getting as iced up and covered with snow. As long as there is large clearance above the unit they work very well under covered area. The manual will tell you what clearance is required above the unit for safe and efficient operation.

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Ask yourself would you want to work on it under the deck?

 

To clarify, the back deck is 6’ by 30’ feet with about 8’ of head clearance. I live in a moderate climate (Seattle). Does being under a deck help with having to deal with fewer nights of frost building on the unit? Being on the side, I need to install as close the house a possible to meet minimum side yard setback requirements. In the back, I can provide additional clearance.

Side yard is pretty much a straight shot through joist to the air handler. From the back, it the lines will run parallel with supply duct.

Thanks.

With the Mitsubishi, I can install on the side. Any other heat pump will need to be installed in the back.