PowerUsageHeat Pump Water Heaters
How HPWHs cut water-heating energy 60–70% vs resistance tanks, where they make sense, and how to schedule them around TOU rates.
Water heating is the second largest energy load in most homes (after HVAC). A heat pump water heater (HPWH) cuts that load by roughly two-thirds compared to a standard electric resistance tank — and unlike most efficiency upgrades, the payback math is fast.
How they work
A standard electric water heater uses a resistance element — same physics as a toaster. Every watt in = one watt of heat. Efficiency tops out at ~100%.
A heat pump water heater is a refrigerator running in reverse: it pulls heat from the surrounding air and dumps it into the tank. The COP (coefficient of performance) is typically 3.0–3.5, meaning every watt of electricity moves 3–3.5 watts of heat into the water.
| Tech | Input power | Heat delivered | Effective efficiency |
|---|---|---|---|
| Resistance electric | 4,500W | 4,500W | 100% |
| Heat pump (heat pump mode) | 500W | 1,500–1,750W | 300–350% |
| Heat pump (resistance backup) | 4,500W | 4,500W | 100% |
| Gas (typical tank) | 36,000 BTU/h | 22,000–25,000 BTU/h | 60–70% |
The catch: heat pump mode is slow. A 50-gallon tank in pure HP mode takes 3–5 hours to recover from a heavy draw. Most HPWHs have hybrid logic that fires the resistance element when demand outpaces the compressor.
What it costs to run
A typical 4-person household uses ~60 gallons of hot water/day, requiring roughly 12 kWh/day of energy delivered (resistance baseline).
| Tech | kWh/day from wall | Annual kWh | Annual cost @ $0.18/kWh | Annual cost @ $0.32/kWh |
|---|---|---|---|---|
| Resistance | 12.0 | 4,380 | $788 | $1,402 |
| Heat pump (COP 3.2) | 3.75 | 1,369 | $246 | $438 |
Savings: $542–$964/year vs resistance, in pure energy alone. HPWH installed cost is $2,000–$4,500 including labor. Payback is typically 3–6 years, sometimes faster with utility rebates (often $500–$2,000) and the federal Section 25C tax credit (30% up to $2,000).
For homes on TOU rates, scheduling can push savings further (see below).
Where they make sense
Good fit:
- Garage, basement, or large utility room (8'+ ceiling, 700+ cubic feet of air).
- Climate zones where the HPWH's cool/dry exhaust is a feature in summer.
- Replacing an existing electric resistance tank (1:1 swap, same circuit usually works).
- Households with predictable hot water use patterns (easier to schedule).
Bad fit:
- Cramped closet with no airflow. The unit pulls heat from the room; a closed closet cools to near-freezing and the unit falls back to resistance mode.
- Conditioned interior space in cold climates. The HPWH "steals" heat from your living space, which your furnace then re-makes — net efficiency drops.
- Replacing a gas tank requires running a dedicated 240V/30A circuit. Add $500–$1,500 for electrical work.
Sizing rule of thumb:
| Household size | Recommended tank | Notes |
|---|---|---|
| 1–2 people | 40 gallon | Smallest common HPWH size |
| 3–4 people | 50–65 gallon | Most popular |
| 5+ people | 65–80 gallon | Larger compressor helps recovery |
HPWHs need a slightly larger tank than resistance for the same household — the slower recovery means more buffer capacity is required to avoid resistance fallback.
Scheduling for TOU
HPWHs are an excellent timeshifting candidate. The compressor draws 400–600W for hours, not minutes — long, low loads are easy to move.
Goal: Heat the tank during off-peak hours, coast through peak on stored hot water.
Three approaches, easiest first:
- Built-in app schedule. A handful of current models expose proper TOU scheduling — not just "vacation" mode, but per-hour heating windows you can set yourself. See the model table below.
- CTA-2045 / EcoPort module. A standardized utility-control port. Plug in a $50–$150 module and the utility can shift heating around grid demand. Some utilities pay $50–$200/year for enrollment.
- Smart plug + thermostat hack. Not recommended — most HPWHs need continuous low-voltage power for their controls. Cutting the 240V supply will trip error codes on many models.
Models with native TOU scheduling
| Model | App / Control | TOU schedule | CTA-2045 port | Notes |
|---|---|---|---|---|
| Rheem Performance Platinum / ProTerra Plus (XE40/50/65/80T10HP) | EcoNet (Wi-Fi built in) | Yes — custom peak/off-peak schedule via app | Yes (EcoPort) | Most flexible scheduling of any HPWH. 5 modes selectable per window. |
| A.O. Smith Voltex XE with CTA-2045 (HPTU-50CTA / 66CTA / 80CTA) | iCOMM | Limited in-app, full schedule via utility CTA-2045 | Yes | Sold under multiple brands — same hardware as State Premier. |
| State Premier Hybrid Electric — Smart Grid Ready (HPX-50/66/80-DHPTCTA) | iCOMM | Same as Voltex (rebranded) | Yes | Often cheaper than the A.O. Smith branded version. |
| GE Profile / Haier UltraHeat (GEH50DFEJSR, current gen) | SmartHQ | Yes — basic schedule + utility opt-in | No (Wi-Fi only) | Cheaper than Rheem; scheduling is less granular. |
| Bradford White AeroTherm RE2H | None (24V dry contact only) | No app | Optional ICON module | Requires an external controller (smart relay, Shelly, home automation) to schedule. Most durable hardware on the list, weakest software. |
| Stiebel Eltron Accelera 300 E | None | No | No | Built-in time clock for basic on/off windows, no app. |
Practical pick:
- Rheem Performance Platinum / ProTerra Plus is the easiest to schedule yourself, no utility program required. If you want to set "heat midnight to 3 PM, sleep until tomorrow" and forget about it, this is the model.
- A.O. Smith Voltex XE-CTA / State Premier CTA are the right choice when your utility runs a CTA-2045 demand response program — you get a check from the utility and off-peak heating, but you give up some control over exactly when it heats.
- Bradford White is for installs where the hot water has to work for 20 years and you don't care about app features — pair with a Shelly relay or Home Assistant for scheduling.
For CTA-2045 utility programs, check PG&E WatterSaver (California), BPA's CTA-2045 program (Pacific Northwest), and the DSIRE database for active rebates and demand response programs in your area.
Example schedule (PG&E E-ELEC plan):
- 12 AM – 3 PM: Heat pump mode active, tank reaches setpoint
- 3 PM – 9 PM: Heating disabled, draw stored hot water
- 9 PM – 12 AM: Partial-peak, heat only if tank drops below ~110°F
This pattern can shift 80–90% of water heating energy to off-peak. At a 16¢/kWh TOU spread, that's another $120–$180/year on top of the HP savings.
Utility programs to check
Many utilities run programs specifically for HPWHs:
- WatterSaver (PG&E) — bill credits for off-peak heating.
- HEEHRA / HOMES rebates — federal IRA program, up to $1,750 for income-eligible households, available through state energy offices.
- Local utility rebates — $300–$2,000 typical, stackable with federal credits.
Check your utility's commercial-grade water heater page (yes, even for residential — that's often where the program is listed) and the DSIRE database for active incentives.
The bottom line
If you have an electric resistance tank, switching to a heat pump is one of the highest-ROI efficiency upgrades available. Payback under 5 years is typical, often under 3 with rebates. Add TOU scheduling and you're saving on rate and timing.
The only setups where HPWHs don't make obvious sense: cramped closets with no airflow, cold-climate interior installs, and homes with cheap gas where the conversion electrical cost dominates the bill savings.
How to use PowerUsage for HPWHs
- Add the water heater as a device. Use the compressor's nameplate wattage (not the resistance element) for "typical" wattage — 500W is a reasonable default.
- Set the schedule to your planned heating window (e.g. 12 AM – 6 AM and 12 PM – 3 PM).
- The TOU breakdown will show how much you're saving by avoiding peak heating cycles.
- Compare against a 4,500W resistance tank running the same hours to see the combined hardware + scheduling savings.