Can a heat pump water heater go in a small closet?

Only if the closet meets one of the four ventilation methods: enough volume, fixed louvers with the required net free area, or ducting. A closet under the minimum volume with a solid door does not comply.

Is backup heat always required?

No. It is required when the inlet air is unconditioned and the compressor cut-off temperature is not below the Heating Winter Median of Extremes for the closest location in JA2 Table 2-3.

Do these rules apply when I replace a gas water heater?

Yes. The compliance manual lists Section 110.3(c)7 among the 2025 requirements for additions and alterations, and Section 150.2(b)1 applies the Section 110.3 requirements to the altered component.

Where Can You Install a Heat Pump Water Heater Under Title 24?

Anywhere the unit can get enough air. Section 110.3(c)7 requires every air-source heat pump water heater to be ventilated by one of four methods and, when its inlet air is unconditioned, to have backup heat. For the 4 kBtu/h compressor the compliance manual uses as typical, that means a room of at least 400 cubic feet, a louvered or vented enclosure, or ducting. The rules are new in the 2025 code and cover replacements as well as new homes.

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Four ways to give it air

The manufacturer’s method, if it performs at least as well as the code’s.
An open room, no ducts: a volume of at least the greater of 100 cubic feet per kBtu/h of compressor capacity or the manufacturer’s minimum.
A vented room: permanent fixed flat-slat louvers or grilles into a neighbouring space that makes up the missing volume, with net free area of at least the larger of 125 square inches plus 25 per kBtu/h or the manufacturer’s figure. Use a fully louvered door, or two equal openings, one in the top half of the enclosure and one in the bottom half, each within 12 inches of the top or bottom.
Ducting: sealed connections, R-6 on exhaust ducts and any duct crossing a pressure boundary, and vents in the room if only the inlet or only the outlet is ducted.

Each method is valid on its own. Several units in one space add their capacities together.

A worked example

Read the compressor capacity from the maker, taken at the AHRI 540 “High” rating point. At 4 kBtu/h an open room needs 400 cubic feet; if the installation manual asks for 350, the larger 400 governs. A vented room needs 125 + (25 × 4) = 225 square inches of openings. A louvered door 26 inches wide with 53 gaps of three-sixteenths of an inch measures 26 × 0.1875 × 53, about 258 square inches, so it passes. Chevron louvers do not count; only fixed flat slats do.

Backup heat

When the inlet air is unconditioned, as in a garage or when drawn from outdoors, backup heat is required unless the compressor cut-off temperature is below the Heating Winter Median of Extremes listed for the closest location in Joint Appendix JA2 Table 2-3. The backup may be built in or external, so resistance elements inside the tank count.

On a replacement

Section 150.2(b)1H adds that the tank stands indoors on a rigid insulated surface of at least R-10 with a communication port, or that the unit meets NEEA Tier 3, a separate option. Both lists are on water heater requirements. An indoor unit draws its heat from the house, which the compliance manual says to count when sizing heating; see HVAC load calculations. Where gas is replaced, electric-ready wiring and all-electric new homes cover the supply side, and permits are the department’s call.

Common Title 24 Questions

Frequently Asked Questions

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