Water heaters
SANCO2 CO2 Heat Pump Water Heater, 83 gal split system
Prices are the equipment only — the appliance, before install labour. Every product in this catalogue currently has at least one real, seller-observed equipment price (see the SKU verification and price observation notes on each product). Get contractor quotes for the install itself, especially for anything needing new electrical circuits or condensate drainage.
Split-system CO2 refrigerant heat pump water heater rated to operate down to -25°F ambient, with a UEF of 3.75.
Our take
This is the answer to the heat pump water heater's biggest weakness. Conventional units put the compressor on top of the tank indoors, which is why they need a big warm room and why they fail in cold garages. SANCO2 puts the heat pump outside like a mini-split and runs CO2 as refrigerant, so it keeps working at -25°F and produces water hot enough that it doesn't need resistance backup at all. It costs roughly double and needs a specialist installer. In climate zone 6 or colder with no good indoor location, it may be the only real option.
Best for
Cold-climate homes with no suitable conditioned space for a conventional heat pump water heater.
Watch out for
Specialist install, limited contractor familiarity, and a price that only makes sense when the alternative genuinely doesn't work.
What sellers are actually charging
Real listings, read on the date shown. Prices change — click through to check before you act on any of them.
| Seller | What you get | Price | Seen |
|---|---|---|---|
| SkipTheWarehouse.com
online retailer |
SANCO2 GS4-83 split system, exact catalogue SKU
GS4-45HPC + SAN-83SSAQA |
$7,355 | 2026-08-16 |
Equipment price is not installed price. The listings above are what the hardware costs. Installation — labour, electrical, refrigerant lines, permits, removing the old system — is typically a similar amount again, and varies more between contractors than between brands. Where we have an installed figure it is labelled as such and comes from someone who actually installs.
What owners and installers report
Collected from trade forums, owner communities and video reviews. Every report links to the original. We synthesise and quote briefly — we don't republish other people's writing.
Cold-weather performance
Whether the unit actually keeps the house warm when it gets cold, and how hard backup heat has to work. On a heat pump water heater this is whether it stays in efficient heat-pump mode or falls back to resistance heat in a cold space.
Thin evidence — too few independent reports to call this a pattern. Shown because it may still be worth asking your contractor about.
Rated to operate to -25°F, but early units had freezing problems in the outdoor compressor loop; the maker retrofitted heat-tape insulation and freeze-protecting relief valves. The remaining failure mode: a power outage during extreme cold can still freeze the compressor even with the tape installed — an installer recommends backup power for the unit.
“the compressor pump will freeze, even when protected by the relief valves” — forum participant trade, 2023-11-20
SANCO2 Heat Pump Water Heater · GreenBuildingAdvisor Q&A · 2023-11-20 · read it in context
Installer/owner consensus: the Sanden makes hot water down to -20°F and can lift incoming water nearly 100°F even at 5°F, but efficiency collapses in the cold — COP falls to roughly 2-3 below 10°F versus 5-6 in warm weather.
“COP in the 2-3 range when below 10F” — forum participant, 2021-05-01
Sanden Sanco2 vs. Standard Heat Pump Water Heater · GreenBuildingAdvisor Q&A · 2021-05-01 · read it in context
Installation and commissioning
How much the outcome depends on the installer rather than the equipment, and what specifically goes wrong.
Thin evidence — too few independent reports to call this a pattern. Shown because it may still be worth asking your contractor about.
Split-system design requires more materials/labor than a unified HPWH, though the article calls it 'basic stuff for plumbers'. Cost ($5,000-$6,000 installed, per the article) is the recurring adoption barrier.
“basic stuff for plumbers” — forum participant trade, 2023-11-20
SANCO2 Heat Pump Water Heater · GreenBuildingAdvisor Q&A · 2023-11-20 · read it in context
Noise in real installations
What owners report hearing, versus the manufacturer's rated sound level. Rated figures are measured under controlled conditions that rarely match a real installation.
Thin evidence — too few independent reports to call this a pattern. Shown because it may still be worth asking your contractor about.
Because the compressor sits outdoors (split system), owners report no indoor noise or cold-air dumping — the complaint that dogs standard indoor-cabinet heat pump water heaters like the ProTerra.
“extraordinarily happy” — Mibici trade, 2023-11-20
SANCO2 Heat Pump Water Heater · GreenBuildingAdvisor Q&A · 2023-11-20 · read it in context
Sources are linked so you can verify any of this yourself. We don't mirror content — Amazon in particular permits no republication of review text, so where we use retailer data we show the aggregate rating and link out. How we collect and weight this →
Compare against
Rheem ProTerra Hybrid Heat Pump Water Heater, 50 gal
The default heat pump water heater for most US households: 50 gallons, UEF 3.75, widely stocked and widely serviced.
Rheem ProTerra Hybrid Heat Pump Water Heater, 80 gal
80-gallon version of the ProTerra, UEF 4.0 — the highest efficiency in the mainstream heat pump water heater market.
A. O. Smith ProLine XE Voltex AL (HPTS-66) Heat Pump Water Heater, 66 gal
66-gallon heat pump water heater with a UEF of 4.02, the highest figure in our water heater set. Sold under A. O. Smith's 'ProLine XE Voltex AL / Smart Hybrid' line — a different, retail-exclusive 'Signature Series' name is used for a different model-number family at Lowe's, so don't cross-shop the names.
A. O. Smith ProLine XE Voltex AL (HPTS-80) Heat Pump Water Heater, 80 gal
80-gallon version of the same ProLine XE Voltex AL 'Smart Hybrid' platform as the HPTS-66 — same compressor and control architecture, larger tank.
Before you buy this
Ask for the first-hour rating, not just tank size, and check it against your household's simultaneous demand — showers and laundry at the same time — rather than headcount alone. If it's a heat pump water heater, confirm the room has enough air volume (or a duct kit) that it won't spend winter on resistance backup, and that there's a real route for condensate, not just a nearby floor drain. Confirm the panel has spare 240V capacity. And if you're removing a gas unit that shared a flue with a furnace, ask what happens to that flue once your water heater's draft is gone — an orphaned flue can backdraft.