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Community and Q&A

Installing a Heat Pump Water Heater: Attic vs. Crawlspace

Moderate | Posted in Mechanicals on

Here in Northern California, Zone 7B, I am prepping for the replacement of my propane water heater to a HPWH.  Due to site conditions and other interior space limitations, I need to install the HPWH either in my insulated but unconditioned garage, or in my vented crawlspace which has plenty of working room due to the 12′ ceilings.  In either scenario, I am wondering if there would be an efficiency advantage to duct the supply air intake to my insulated at the ceiling and vented attic space?  The attic has southern exposure, so in my climate it would seem that either summer or winter there would be warmer air available there than where the water heater would reside.  The attic has about 4′ of headroom, so the duct could be installed well above the insulation to keep the intake air clear.  Is this advisable?
Thank you

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  1. Expert Member
    Dana Dorsett | | #1

    California climate zone 7 is entirely within IECC climate zone 3B. See:

    Where is the HPWH exhaust being vented? If it is vented into the conditioned space it will pressurized the conditioned space, driving exfiltration whenever it runs, throwing away any potential air conditioning benefit, and putting potentially contaminated attic air into the house.

    As a general rule it would be better from both an energy efficiency and indoor air quality point of view to have BOTH the intake and exhaust either in the attic, or inside of conditioned space, even if you have to duct the intake in from another (larger) room to cover the volume needs of the HPWH.

    1. Moderate | | #2

      Thank you for the reply. The HPWH exhaust could be vented into the garage for some cooling, but given the air coming from the attic could contain various particulates, I would opt to exhaust into the attic or through the garage wall to the exterior.

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