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I am getting ready to replace my current hot water heater - it is a ~15 year old tank gas water heater so I want to be prepared in case it breaks. In the summer (when I am not using gas to heat the house) I pay on average $20 per month for gas, so as a first-order approximation I pay ~$240 a year for hot water.

I also have solar panels, and currently pay nothing for electricity except for the connection fee. My electrical provider offers net metering, so excess electricity made in the summer months count towards the winter months. I haven't had the panels for a whole year so I cannot be sure that I generate a net positive amount of electricity yearly, but it is trending that way at this time. So, for the purposes of this comparison, electricity is currently either free or very cheap, but the addition of an appliance that uses a large amount of electricity could change that.

I am trying to decide whether I should replace my current tank gas water heater with a heat pump electric water heater, or with another gas water heater (of some type).

Everything I have read about electric heat pump water heaters is that they offer significant energy savings over conventional electric water heaters. I have not been able to find a direct comparison of energy used by a heat pump water heater compared to a gas water heater, so it's not clear to me if I would see any savings (either money or energy) over what I currently pay/use. In terms of potential gas water heaters, I am pretty open to any of tank, tankless, or condensing - my primary interest is saving energy and lowering monthly costs, and am OK with a large up-front cost if need be.

Taking into account that I have solar power (e.g. cheap electricity) but also have gas already set up, which of heat-pump electric or gas water heaters is likely to be the most efficient and least expensive to operate?

Update

Answers to some questions

  • Current water heater is in the garage, and that is where the replacement will go
  • Home heating uses gas
  • I am looking at hybrid heat pump water heaters.

Basically, my question boils down to the following: it is known that going from conventional to heat pump electric means savings, and going from conventional electric to gas means savings, but it is not clear to me in what direction the savings flows when going from gas to heat pump electric.

  • Check out solar thermal panels - sunshine to heat is more efficient than sunshine to electricity... – Solar Mike Jun 30 at 7:06
  • You really have not provided enough information to determine which solution is best from an economic viewpoint. You've only provided generalities. It's not just the operating cost of the solution you choose. It's also the equipment and installation costs, the maintenance, the service lifetime, tax credits, etc. – jwh20 Jun 30 at 10:29
  • Are you looking only at hybrid heat pump water heaters, or are you looking at split system heat pump water heaters as well? Also, how do you currently heat your house? – ThreePhaseEel Jun 30 at 11:45
  • Check out noise levels with a heat pump WH; also reliability. What is the location of the gas WH? If it is in a small closet, then that might not allow replacement with a heat pump. – Jim Stewart Jun 30 at 12:17
  • You can’t just multiply your gas bill by 12 to allocate water heater use. First, there’ll be connection charges that you would pay even if you used zero gas. Second there is usage by other appliances (range/oven/dryer). If all that other stuff is electric, then look at the bill details, and see actual gas used midsummer. Also, I wouldn’t say a WH is about to go merely because it’s 15 years old. – Harper - Reinstate Monica Jun 30 at 15:11
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If you gas to heat the hot water is only $20 a month, It would not make economical sense to change to a heat pump. The cost of a gas water heater would be roughly 1/3 or less the cost of a hybrid heat pump. The gas has low maintenance, just yearly flushing and maybe anode replacement. Gas has a fast recovery time. The hybrid heat pump would require 220 v circuit, has a shorter life cycle, very slow recovery time unless the electric elements are turned on, then it would still be slower than gas. Trying to save $20 a month with a $2000 hybrid water heater with all its short coming would not be practical.

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Is your water heater inside the home or outside? I ask this because heat pumps use heat transfer using the heat of the area they are in to create heat.

Ok to put it more simply if the water heater is inside the home when the water heater is extracting heat to store in the tank it is cooling that area just like an air conditioner would. So are heat pumps more efficient inside the home envelope barely when compared to electric but compared to gas it will cost more. Also remember that 15 year old gas water heater that is still running , you now have a fancy electronic controlled thermal transfer system with a compressor to pump the process, do you think that will last as long as a new simple gas water heater?

I would gladly go back to gas, faster recovery and less monthly cost. I you might think well I don’t like electric stuff. I am a professional electrician that also has universal 608 and 609 (HVAC&R & MVAC) licensees and I like gas better.

The only possible advantage is your electric utility may have incentives to go heat pump usually electric to electric but check. My utility paid 99% of me installing my unit but I am licensed so most of the install cost was just my time. Edit they gave me most of the cost of the heat pump unit.

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The #1 factor in water heater life isn’t raw age (and 15 isn’t exactly geriatric), it’s maintenance of anode rods.

Heat pump water heaters aren’t free. They just change the piper you are paying.

As Ed Beal says, heat pump water heaters are basically air conditioners that have the “hot side” in a big tank of water. That’s awesome when you want to run air conditioning, throw the utility room door open and enjoy the cool! However, when you want heat, the HPWH is stealing your heats, working against your furnace.

And worse, if you bottle the HPWH inside a utility room, it will quickly turn the utility room into a refrigerator, at which point it stops working. You must actively heat the utility room!

That is working as intended: the environmental logic of this is that most places have gas heat, so you’re turning 90% of the gas’s energy into water heat, instead of the the 33% you get from converting gas to electricity at a gas thermal power plant. (Turning gas into heat is easy; turning heat into electricity is hard).

Obviously this is an ignominious fail if the house has pure electric heat-strip heating.

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  • I don't actually think it's doomed - I softened the language in the question to reflect that I am a planner and want to have a plan for when I do need to replace rather than scrambling at the last minute. – SethMMorton Jun 30 at 15:42
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Depends a LOT on your local costs - in many places, natural gas is quite inexpensive on an "energy basis" but against "nearly free" electricity that might not hold.

Then there's the upfront costs of the heat pump water heater (fairly expensive) .vs. a gas water heater (boringly normal.) While you are OK with a large upfront cost, in cases of slight savings per month you may never recoup a large upfront cost increase before it's time for the next water heater.

Finally, there is house heat in heating season (presumably gas?) and whether you cool or would like at least some cooling in the summer - the heat pump water heater cools air, so it contributes to A/C, but also adds (slightly) to your heating load in the winter.

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