Heat Pump vs Gas Water Heater
The heat pump uses a fraction of the energy. The gas tank refills faster and fits anywhere. Your basement decides which of those you can have.
Heat & Tap earns a commission on qualifying purchases made through the Amazon links on this page, at no extra cost to you. Commission does not decide what we recommend or how we rank it. Full disclosure.
Buy a heat pump water heater if you have the space for it. The Rheem ProTerra 50 publishes a 3.88 UEF against roughly 0.58 to 0.62 energy factor for an atmospheric gas tank — it moves heat rather than making it, so it uses a small fraction of the energy per gallon. Buy the gas tank if the space is tight, cold, or the recovery has to be fast: the A. O. Smith Signature 100 delivers 91 gallons in the first hour against the ProTerra's 67.
This is the comparison that has replaced tankless-vs-tank as the one worth having. A heat pump water heater is an air conditioner pointed at a tank: it takes heat out of the surrounding air and puts it into the water, which is why its efficiency figure is above 1.0 and a burner's never can be. The catch is everything around it — air volume, temperature, noise, a condensate drain, and headroom.
Side by side on published figures
| Rheem ProTerra 50 | A. O. Smith Voltex AL, 66 gal | A. O. Smith Signature 100, 50 gal gas | |
|---|---|---|---|
| Energy source | Electric heat pump with element backup | Electric heat pump | Natural gas |
| Efficiency | 3.88 UEF (up to 4.07 advertised on 30 A models) | Highest published in our registry | Not published on the retail listing; the category runs 0.58 - 0.62 EF |
| Capacity | 50 gallons | 66 gallons | 50 gallons |
| First-hour rating | 67 gallons | 82 gallons | 91 gallons (77 on the 40,000 BTU model) |
| Recovery | 27 gal/h | Not published separately | Gas recovery, not published separately |
| Backup element | 5,000 W | Yes | Not applicable |
| Ambient operating range | 37 - 145°F | Northern Climate Specification Tier 4 | Not temperature dependent |
| Venting | None — but it needs air volume | None — but it needs air volume | Atmospheric chimney or B-vent |
| Leak protection | Integrated detection with auto shutoff, leaks limited to 20 oz | Leak protection included | None |
| Warranty | 10-year limited | Not published on the sheet we hold | 6-year tank and parts; 9-year on the 40,000 BTU model |
Two rows carry the decision. The efficiency row is why anyone considers a heat pump at all. The first-hour row is why gas still wins in a busy house: 91 gallons against 67 is roughly one and a half extra showers before the tank falls behind.
Quick picks
Tap any row to read the full assessment below, or go straight to Amazon from the right-hand column. We earn a commission on qualifying purchases at no extra cost to you.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | Rheem ProTerra 50 gal hybridThe heat pump water heater to start with: a 3.88 UEF, a 67-gallon first-hour rating, and a 37°F lower operating limit that is the widest ambient range in its class — which is the specification that decides whether it works in a cold garage. | Most heat pump installs | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  A. O. Smith Signature 100, 50 gal gasThe straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one. | Most gas tank replacements | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 3 |  A. O. Smith Voltex AL, 66 galThe efficiency leader on this page at 4.02 UEF, in the capacity that suits a five- or six-person household, with a heavy-duty anode rated to protect the tank for 10 years. | Highest published heat pump efficiency | Check price on Amazon No live price feed on this site, so we show none. #ad |
The three units in full
Pick 1 — Most heat pump installs
Rheem ProTerra 50 gal hybrid
The heat pump water heater to start with: a 3.88 UEF, a 67-gallon first-hour rating, and a 37°F lower operating limit that is the widest ambient range in its class — which is the specification that decides whether it works in a cold garage.
| Capacity | 50 gallons |
|---|---|
| Efficiency | 3.88 UEF; up to 4.07 UEF advertised on 30 A models |
| First-hour rating | 67 gallons |
| Recovery | 27 gallons per hour |
| Heat pump capacity | 4,200 BTU/h |
| Backup element | 5,000 W |
| Voltage | 208 - 240 V |
| Ambient operating range | 37 - 145°F |
| Cold-climate rating | Meets Northern Climate Specification Tier 4 |
| Leak protection | Integrated detection with factory-fitted auto shutoff; leaks limited to no more than 20 oz |
| Warranty | 10-year limited |
What is good
- A 37°F lower limit means the compressor keeps running in an unheated garage through most of a northern winter
- 3.88 UEF is roughly four times a resistance tank, so the running cost difference is not marginal
- 67-gallon first-hour rating is better than most 50-gallon resistance tanks
- EcoNet control lets you force high-demand mode before guests arrive instead of discovering the limit
What is not
- It is a refrigeration appliance in your house: there is a compressor, a fan and a condensate drain
- Needs roughly 700 cubic feet of air, or louvered doors, in a closet
- It cools and dehumidifies the space it stands in, which is a gift in a Houston garage and a problem in a Minnesota basement
Skip it if: Skip it if the only place it can go is a finished, heated room you occupy. It will steal heat from that room in winter — your furnace then pays for the hot water, and the efficiency you bought disappears.
No live price feed on this site, so we show none. #ad
Specifications above from Rheem ProTerra PROPH50 T2 RH375-30 product page; ABR Wholesalers listing, PROPH50 T2 RH375-30. We have not tested this unit ourselves.
Pick 2 — Most gas tank replacements
A. O. Smith Signature 100, 50 gal gas
The straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one.
| Capacity | 50 gallons |
|---|---|
| First-hour rating | 91 gallons (50,000 BTU model); 77 gallons (40,000 BTU model) |
| Burner | 50,000 BTU/h ultra-low NOx, or 40,000 BTU/h |
| Dimensions | 61 in H x 22 in dia (50,000 BTU); 60-3/4 in H x 22 in dia (40,000 BTU) |
| Warranty | 6-year tank and parts with 1-year labor (50,000 BTU); 9-year tank and parts with 2-year labor (40,000 BTU) |
What is good
- A 91-gallon first-hour rating from a 50-gallon tank covers back-to-back showers that empty an electric tank of the same size
- Widely stocked at Lowe's, so same-day replacement is realistic when the old one fails
- Ultra-low NOx burner meets the stricter air-district rules in California and Texas
- 22-inch diameter fits most existing alcoves without re-plumbing
What is not
- The longer 9-year warranty is on the smaller burner, so warranty and recovery pull in opposite directions
- Atmospheric venting needs a working chimney or B-vent
- Standing pilot and flue losses mean it idles energy away all day
Skip it if: Skip it if your water heater sits in a sealed closet or a space with combustion air problems. An atmospheric gas tank needs real combustion air and a real flue — the power-vent or direct-vent models exist for exactly that case.
No live price feed on this site, so we show none. #ad
Specifications above from Lowe's listing, Signature 100 50-gal 50,000 BTU; Lowe's listing, Signature 100 50-gal 40,000 BTU 9-year. We have not tested this unit ourselves.
Pick 3 — Highest published heat pump efficiency
A. O. Smith Voltex AL, 66 gal
The efficiency leader on this page at 4.02 UEF, in the capacity that suits a five- or six-person household, with a heavy-duty anode rated to protect the tank for 10 years.
| Capacity | 66 gallons |
|---|---|
| Efficiency | 4.02 UEF |
| First-hour rating | 82 gallons |
| Cold-climate rating | NEEA Northern Climate Specification Tier 4 qualified |
| Anode | Heavy-duty smart anode, adapts to local water conditions; rated to protect the tank for 10 years |
| Connectivity | iCOMM smart connectivity with app and display |
| Leak protection | Leak detection, with an optional automatic water shutoff |
| Warranty | 10-year limited |
| Certification | ENERGY STAR certified |
What is good
- 4.02 UEF is the highest figure of any unit in this registry, and an 82-gallon first-hour rating with it
- 66 gallons removes the recovery anxiety that a 50-gallon heat pump creates in a big household
- The 10-year anode is a real durability claim, not a marketing one
- ENERGY STAR certification keeps it inside most utility rebate lists
What is not
- 66 gallons is a tall, wide cabinet — measure the space before you order
- Sold mainly through wholesale, so availability is slower than big-box
- No numeric ambient operating range is published, so cold-garage suitability rests on the NEEA Tier 4 qualification rather than on a stated lower limit
Skip it if: Skip it if your install space is a closet. A 66-gallon heat pump needs air volume to work, and starving a heat pump water heater of air is how you end up running on the backup element and paying resistance rates for a premium appliance.
No live price feed on this site, so we show none. #ad
Specifications above from Auer Steel listing, A. O. Smith HPTS-66 Voltex AL; A. O. Smith Voltex AL introduction; First Supply listing, A. O. Smith HPTS-66 Voltex AL. We have not tested this unit ourselves.
What a heat pump needs that a gas tank does not
- Air volume. A heat pump water heater cools and dries the air it draws from. Manufacturers specify a minimum space or ducting; a sealed closet starves it and it falls back on the resistance element, which is the expensive way to run it.
- Headroom. These units are taller than the tank they replace — plan on around seven feet of clear height for a 50-gallon model and more for a 66 or 80.
- A temperature floor. The ProTerra operates from 37°F, which is the widest ambient range in its class and the specification that decides whether it works in an unheated garage in January. Below that it is running on the element.
- A condensate drain. It makes water the way an air conditioner does, and that water has to go somewhere.
- Tolerance for noise. It is a compressor and a fan. Our page on heat pump water heater noise has the published figures.
What the gas tank gives you instead
- Recovery. 91 gallons in the first hour from 50 gallons of storage is the strongest number on this page, and it comes from the burner, not the tank.
- It fits where the old one fitted. 61 inches tall and 22 inches in diameter drops into most existing alcoves without re-plumbing.
- It does not care how cold the room is. A garage at 30°F is a non-event for a gas tank and a problem for a heat pump.
- Same-day availability. Stocked at Lowe's, which matters when the old unit failed this morning.
- It needs a flue. That is the cost on the other side of the ledger, and in a sealed closet it is a disqualifier.
Where each one belongs
| Your situation | Pick | Why |
|---|---|---|
| Garage or basement, 7 ft of headroom, mild or warm | Rheem ProTerra 50 | 3.88 UEF, a 37°F ambient floor and integrated leak shutoff |
| Large household, electric only, space available | A. O. Smith Voltex AL, 66 gal | 82 gallons in the first hour without giving up heat pump efficiency |
| Existing gas line, 3+ people, tight alcove | A. O. Smith Signature 100, 50,000 BTU | 91-gallon first-hour rating in a 22-inch footprint |
| Unheated space that drops below freezing | Gas tank | A heat pump below its ambient floor is just an expensive resistance tank |
| Sealed interior closet | Gas tank, direct vent — see water heater venting | Neither atmospheric gas nor a heat pump can breathe in there |
| You are weighing a heat pump against going tankless instead | Read heat pump vs tankless | Different problems: running cost against endless supply |
If you are on electricity today and the question is really whether the heat pump premium pays back, are heat pump water heaters worth it? works through the conditions, and heat pump vs electric tank is the straight like-for-like.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Drain pan
A heat pump water heater makes condensate continuously, so this one is not optional.
- Leak detector
A condensate line that blocks will overflow long before you notice it.
- Expansion tank
Same closed-system rule as any other storage tank.