Can heat-pump water-heater exhaust go into an attic or near soffit vents?

MGI’s recommendation: Have the exact intake and exhaust plan reviewed before adding ductwork. Attic routing can be permitted for some equipment, but the model instructions and the home’s air paths need to support the complete design.

A. O. Smith’s August 2022 hybrid manual permits some air routing to an attic, outdoors, or another room, with specific duct requirements. It also prohibits routing exhaust from a garage or an area with potentially harmful fumes into other building spaces. Permission in one situation is not approval for every attic installation. A. O. Smith hybrid installation guide, ducting considerations

Start by naming where the heater draws air, where it exhausts air, and which spaces are connected. A sketch should include the attic, soffit vents, nearby openings, and any fuel-burning equipment. Ask the qualified installer to explain the intended airflow and whether the route changes pressure in the home or an adjacent space.

For an exterior termination near soffits, ask whether the discharged air could enter the attic or return to another intake under the actual layout. The review should consider moisture, outdoor conditions, airflow, and the termination requirements that apply to the equipment and building. A generic distance copied from an unrelated exhaust system is not a design.

Require the applicable manual revision, approved adapters, duct size and length limits, and the installer’s assessment of the proposed route. Ask who checks roof or wall penetrations, weather protection, and any insulation or building work. Those tasks need qualified owners and coordination in the quote.

Do not connect the heater to an existing duct or vent simply because it is nearby. Do not improvise termination screens or duct reductions. The proposal should demonstrate that the heater can move the required air through the entire approved route.

Our preference would be the simplest approved arrangement that fits the home without creating another air or moisture problem. An attic path can stay on the options list when the model and site support it; otherwise, compare another location or routing plan.

Send the full model number and proposed drawing to the installer. Ask for the design approval basis and final verification plan before authorizing separate duct or building work.