Best Heat Pump intake with sealed attic
We are installing a heat pump water heater in a small, insulated conditioned basement room dedicated for the water heater in Building Climate zone 16 in California. The water heater room is too small for the intake requirements, so our options are to a) run an intake vent up a chase through a closet to the sealed attic or b) sideways through the water heater room into uninsulated, unsealed space under the house. Exhaust is planned to go into space under house. One of our concerns is whether the negative pressure from the intake (plus all other negative pressure vents, e.g., shower, kitchen hood) will create any other problems. We would like to ensure water heater efficiency and the HVAC team is saying the intake from the crawlspace is good enough given the efficiency of the unit. Thoughts? Unit is to Rheem pro terra hybrid electric.
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Most of California is climate zone 3. See: https://www.homerenergy.com/products/grid/docs/1.3/images/hmfile_hash_d10d1726.png
For some reason it seems common that plumbers believe HPWH need to be vented to the outside. I guess they're used to dealing with gas.
It should be pulling air from conditioned space and venting into conditioned space. Can you put a grill on the water heater room? That's the easiest solution.
Agree with DC,
Additionally, I would not duct the exhaust of the water heater outside of the water heater room. It is conditioned and dehumidified air, I would want to use that as the supply air for this mechanical closet in the crawlspace.