With the moratorium on fossil fuel equipment, electric water heaters are now the only game in town. There, you have a few choices, but not really any good choices. You are basically limited to; old school electric tank heaters, electric instant (tankless), and electric heat pumps. Each has their drawbacks and sometimes those drawbacks make them unsuitable for common applications. Here’s my opinion of where each one stands…
Electric Tank Water Heaters
I’ll start with the “old faithful” electric tank water heater. On the positive side, they are dirt cheap relative to all other water heaters, but that’s about it for positives. It will cost about twice as much to run as an oil-fired unit and almost four times as much as a natural gas unit. The recovery rate (how long it takes to reheat after you use it) is mediocre at best compared to even the cheapest fossil fuel heater, but it’s functional for most typical builds. If you need more hot water, you get a bigger tank. However, If you are building in the Hamptons with a stretch code… it will trash your HERS rating, and you’ll end up needing to add solar PV to offset the efficiency losses. Also note… if your water tank is over 55 gallons, it must be a “smart” grid-tied unit to meet federal efficiency requirements. The commercial 75-gallon units that builders are installing aren’t technically legal in residential homes.
Electric Instant (Tankless) Water Heaters
Tankless heaters create the same horrors for your HERS rating, but they do have the benefit of never running out of hot water. The downside? They draw crazy-massive amounts of electricity and yet still have limited GPM flow rates. For comparison, a standard gas wall-hung heater, like a Navien 240, will supply just under 200,000 BTU of heat to make hot water. The largest “off the shelf” residential electric instant is about 120,000 BTU and it requires 4 – 40amp circuits (160 amps) to run. That 160 amps will give you about 5gal/min. Enough for two low-flow shower heads, but that’s about it. Good for a smaller home or that “one bath on the other side of the house” but probably not going to cut it for larger homes.
Residential Heat Pump Water Heaters
So that leaves us with heat pump water heaters. They look like regular tank water heaters with a tiny little heat pump unit on top. These are a little bit of a different animal, so they need to be thought out carefully. First off, they have amazingly small heat pump units… about 4,000 BTU. Compare that to the Navien unit mentioned above, and you can see that “abundant hot water” isn’t in your future. Basically… it will spend all night heating up the tank so you have hot water in the morning. If you run out, expect to wait till dinner before it’s hot again. They have hybrid models that add a couple of resistance coils in, but there goes your energy savings. At the end of the day, you still have slow recovery compared to a fossil fuel unit.
Another consideration… you have to think about where you are putting these units. They take heat from the surrounding air to put into the water. If you put them in a closet or small room, you’re not going to get the efficiency they promised you on the box, and you’re going to run into some crazy issues with interstitial condensation and its best friend… mold. You’re also going to need to make sure the heat pump that’s warming the room the water heater is in is large enough to also provide the 4k BTU that’s going into the hot water. I know, it sounds counter-intuitive, but that’s the way it works. In an older home, it would just draw the heat from what leaks into the basement and absorb the heat that your boiler or furnace gives off in jacket losses. But in a new, tight, all electric home, there isn’t any of that. So, in effect, you are paying to heat the room air and then again to put it into the water. I’m not sure how that’s efficient, but that’s the way it works. In the summer, your water heater will provide a little extra AC for the building, but the rest of the time you’ll be supplying the heat from your home heating system.
Commercial Split-System Heat Pump Water Heaters
There is another option – an expensive option, that’s best suited for really large homes or really high use situations. You have the option of using commercial grade split system heat pumps. On the larger side, Mitsubishi sells a “Heat2O” unit with a 204k BTU output (about the same as the Navien we discussed before) with a tank size up to 500 gallons. What’s the catch? You need a 70 amp 3-phase circuit to run it. If you are building big and already planning on City-Multi units for HVAC, this might be exactly what you were looking for. Otherwise, adding a phase generator to get the 3rd phase might just be too much to make this practical.
Going down a size, Mitsubishi is bringing over from Europe their “Ecodan” line which looks promising since it’s a packaged air/water unit that can be used for water heating, radiant heat, etc. They are available (in Europe at least) up to about 45k BTU. It’s “coming soon” sometime at the end of 2025. I’ll post an update once I get more info.
At the other end of the spectrum, downright tiny compared to the Heat2O, there are the SanCO2 Gen5 split units. These have a 15.4k BTU compressor which is still tiny, but a big step up from the “pump-on-top” 4k BTU units they have sitting at the plumbing supply. There’s still a catch to this one also… a $6,000 price tag, but it might be an option if you really want hydronic radiant in some of your floors.
I haven’t spent too much time hunting down other options, but I’m sure they exist. A trip to the supply house might yield some happy surprises, or at least a few more options. At the end of the day, making hot water without fossil fuel is do-able. To paraphrase an old movie, “We’re doing it, but we ain’t diggin’ it”. It’s not going to save anyone any money, but clearly that wasn’t what the powers-that-be were worried about when they made the law. But … Like everything else, we’ll get used to it.
Tom