Water HeatersHeat Pump
A. O. Smith CAHP-66 2 Water Heater Manual
Setup, everyday use, maintenance and troubleshooting for the 68-gallon heat pump water heater, with verified specifications.
- UEF3.84
- Tank68 gal.
- First-hour rating83 gal.
- Est. yearly cost$220
About the A. O. Smith CAHP-66 2
A. O. Smith model CAHP-66 2 is a 68-gallon heat pump water heater that meets ENERGY STAR efficiency requirements.
It stores 68 gallons and has a first-hour rating of 83 gallons — the amount of hot water it can supply in one busy hour starting with a full tank. The DOE classifies it in the high usage draw pattern, so its efficiency rating assumes about 84 gallons of hot water a day.
Its UEF of 3.84 means it moves about 3.84 units of heat into the water for every unit of electricity, by drawing heat from the surrounding air. A standard electric-resistance tank scores roughly 0.9 to 0.95. That UEF is higher than 68% of the 595 heat pump models in our database.
As an integrated unit, the compressor sits on top of the tank and pulls heat from the surrounding air, cooling and dehumidifying the room slightly as it runs. Its rated electric input is 4.5 kW at 240 V (22.0 A maximum). The compressor operates down to 37 °F; outside that range backup resistance heat takes over. Refrigerant: R-134a (GWP 1,430). It is connected-capable (CTA-2045) and supports CTA-2045-A and CTA-2045-B demand-response communication, so it can take part in utility programs that shift water heating to off-peak hours.
Specifications
| Brand | A. O. Smith |
|---|---|
| Model number | CAHP-66 2** |
| Water heater type | Heat Pump |
| Heat pump configuration | Integrated, 240 V |
| Fuel / energy source | Electric |
| Storage volume | 68 gal. |
| First-hour rating | 83 gal. |
| DOE draw pattern | High-Usage |
| Uniform Energy Factor (UEF) | 3.84 |
| Estimated annual electricity use | 1,292 kWh/yr |
| Rated electric input | 4.5 kW |
| Voltage | 240 V |
| Maximum current | 22.0 A |
| Compressor low-temperature cut-off | 37 °F |
| Refrigerant | R-134a (GWP 1,430) |
| Tank height | 61.0 in. |
| Tank diameter | 23.0 in. |
| Connected / demand-response capable | Yes |
| Connectivity | CTA-2045 |
| Demand-response protocol | CTA-2045-A and CTA-2045-B |
| Load-up functions | Advanced load-up |
Safety information
- Set the water heater to about 120 °F (49 °C). Water at 140 °F can cause a serious burn in a few seconds; at 120 °F it takes several minutes. Homes with young children or older adults benefit from anti-scald valves at tubs and showers.
- The temperature and pressure (T&P) relief valve protects the tank from bursting. Never cap, plug or remove it, and keep its discharge pipe running full size to within about 6 in. of the floor or to an approved drain.
- Installation should be done by a licensed plumber (and electrician or gas fitter where required). Most jurisdictions require a permit.
- Turn off the breaker before removing any cover. Never switch on power to an electric water heater until the tank is completely full — an element energized in air burns out in seconds.
- Where local code requires it (for example, in seismic zones), secure the tank to the wall with approved strapping.
Installation and first-time setup
Use this checklist when planning the installation of the A. O. Smith CAHP-66 2 and when reviewing the finished job with your installer.
- Choose a space with enough air
Integrated heat pump water heaters need a large volume of air or ducting — often around 700–1,000 cubic feet, but follow your manual. Basements, garages and large utility rooms work well; a closet usually needs louvered doors or ducts. The compressor stops below 37 °F, so very cold spaces push the unit onto backup heat.
- Leave service clearance
Keep space above and around the unit for airflow and for removing the air filter. The tank is 61 in. tall and 23 in. in diameter, so check ceiling height and doorways before delivery.
- Condensate drain
The evaporator removes moisture from the air. Route the condensate line to a floor drain or condensate pump; the amount can be significant in humid weather.
- Electrical supply
Provide a dedicated 240 V circuit sized by an electrician to the nameplate (maximum current 22.0 A); under the National Electrical Code, water-heater circuits are sized at 125% of the rated load.
- Plumbing connections
Use dielectric fittings where dissimilar metals meet, install a shut-off valve on the cold inlet, and pipe the relief valve discharge to an approved location. Add an expansion tank if the supply has a check valve or pressure-reducing valve.
- Fill and purge before start-up
Fill the tank completely and run a hot tap until water flows steadily, so no air remains, before turning on power. Then set the temperature and check every joint for leaks.
Using your water heater
Operating modes
Most heat pump water heaters offer an efficiency (heat pump only) mode, a hybrid or auto mode that adds backup heat when demand is high, a high-demand mode, and a vacation mode. Mode names differ by manufacturer, so check your manual. Use the most efficient mode that keeps up with your household, and switch to hybrid or high demand only when guests are staying.
Heat pump recovery is slower than an electric element. If you run short of hot water, raise the setpoint a few degrees with a mixing valve installed, or use hybrid mode during peak times rather than leaving the unit in resistance-only mode. When the surrounding air falls below 37 °F the compressor pauses.
Expect cool air from the unit's exhaust and a gentle fan and compressor hum. In summer the cooling and dehumidifying effect can be a bonus in a basement; in a heated space during winter it slightly increases the load on your heating system.
Saving hot water and energy
- Fix dripping hot-water taps promptly and use WaterSense showerheads and faucet aerators.
- Insulate the first several feet of hot and cold pipes at the heater.
- Wash laundry in cold water when possible.
- Enroll in your utility's demand-response program if one is available; this model's advanced load-up functions let it heat ahead of peak periods while keeping hot water available.
Care and maintenance
| When | What to do |
|---|---|
| Every year | Test the T&P relief valve by lifting its lever briefly with a bucket under the discharge pipe; if it does not reseat and stop dripping, have it replaced. |
| Every year | Drain a few gallons from the tank drain valve, or flush it fully, to remove sediment — more often in hard-water areas. |
| Every 2–3 years | Have the anode rod inspected and replaced when it is heavily corroded; this is the main defense against tank corrosion. (Some models use a powered anode — follow the manual.) |
| Every 1–3 months | Clean the air filter on the heat pump section as the manual directs, and check that the condensate drain flows freely. |
Troubleshooting
Check these common causes before calling for service.
| Problem | Possible cause | What to try |
|---|---|---|
| Not enough hot water | Efficiency mode cannot keep up with demand; setpoint low; very cold air around the unit. | Switch to hybrid or high-demand mode temporarily; raise the setpoint slightly with a mixing valve; improve air supply to the unit. |
| Unit seems to run constantly | Normal for heat pump recovery, which is slower than an element; dirty air filter. | Clean the filter. Long run times at low power are expected. |
| Water around the base | Blocked condensate line; leaking fitting; relief valve discharge. | Clear the condensate drain and check fittings; a leaking tank must be replaced. |
| Fault or alert on the display | Sensor, airflow or element fault detected by the controls. | Note the code and look it up in the code table in your manufacturer's manual. |
| Rotten-egg smell in hot water | Bacteria reacting with the anode rod or water chemistry. | Flush the tank; a plumber can replace the anode with a different alloy or treat the water. |
| Relief valve dripping or discharging | Excess pressure from thermal expansion; failing valve; temperature set too high. | Have the pressure checked and an expansion tank added if needed; replace a faulty valve. Never plug it. |
Energy use and running costs
The A. O. Smith CAHP-66 2 is estimated to use 1,292 kWh per year, about $220 a year ($18.30 a month) at $0.17 per kWh.
A standard electric-resistance tank with a UEF of about 0.92 would need roughly 5,393 kWh to deliver the same hot water — about $697 more per year.
These estimates come from the DOE test, which assumes 84 gallons of hot water a day heated from 58 °F to 125 °F; your use will differ. Heat pump performance also depends on the temperature of the air around the unit and on how often backup heat runs.
Frequently asked questions
How much hot water does the A. O. Smith CAHP-66 2 provide?
It has a 68-gallon tank and a first-hour rating of 83 gallons, which is the best guide to how it handles a busy morning.
What is the UEF of the A. O. Smith CAHP-66 2?
Its Uniform Energy Factor is 3.84, measured in the DOE high usage draw pattern. Values above 1 are possible because a heat pump moves heat from the air rather than generating it.
How much does it cost to run the A. O. Smith CAHP-66 2?
About $220 a year, based on its estimated 1,292 kWh/yr and electricity at $0.17/kWh.
What electrical supply does the A. O. Smith CAHP-66 2 need?
It needs a dedicated 240 V circuit for a maximum current of 22.0 A, sized by an electrician to the nameplate.
Can the A. O. Smith CAHP-66 2 be installed in a cold garage?
Its compressor operates down to 37 °F. Below that, it relies on backup heat, so a garage that regularly drops below that temperature will reduce its savings.
Does the A. O. Smith CAHP-66 2 support utility demand-response programs?
Yes. It is connected-capable (CTA-2045), it supports CTA-2045-A and CTA-2045-B demand-response communication, it offers advanced load-up functions, and it can follow a time-of-use schedule.
Is the A. O. Smith CAHP-66 2 ENERGY STAR certified?
Yes. It appears on the ENERGY STAR certified water heater list, with a certification date of August 2026.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified water heaters dataset published by the U.S. Environmental Protection Agency (record certified August 12, 2026), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with A. O. Smith. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact A. O. Smith or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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