Heat Pump Water Heaters, Worth it?

Not strictly a HASS question but I figure there are lots of people on here closely monitoring energy usage of their appliances and I was wondering if anyone has collected data on the actual difference in energy consumption when installing a heat pump hot water tank?

Considering an upgrade but where I live power is cheap and a heat pump water heater costs 4.5X the price of electric. The delta in price is equivalent to the cost of 24.5 Megawatt-hours of electricity.

Any data and discussion on this topic would be appreciated!

I recently changed my ~10yo water heater by heat pump backed water heater.

  • Before: 4.9kWh/day (including 2kWh/day when absent from home)
  • Now: a bit less than 2kWh/day (including < 0.5kWh/day when absent from home).

I live in France so electricity is quite cheap as well. I think it is worth doing the investment (since it improves heating in general of the house and reduce co2 emissions).

I have a similar related question that a HA user may have already done the math on.

Is a typical domestic instant gas hot water heater (non storage) more or less ‘costly’ (not efficient) to run per day than an electric heat pump storage hot water heater ?

I have not found an answer online anywhere, just claims that they are more energy efficient which I don’t have any doubts on, but that’s not the same as cheaper to run.
I guess if I knew what the typical average daily gas energy usage in MJ I could work out the rest…

Exactly. Heating water with gas or electricity is both very efficient. And having no storage (but heating always/only on demand) is also “more” efficient as there is no “loss” of hot water which cools down in the tank and needs to be re-heated. :arrows_counterclockwise:

The advantage with a heat pump is that you put like 1kWh of power in but get like 3 or 4 times the amount out in terms of heating power. To my knowledge this can only work with a hot water tank so you will have losses in the hot water storage. :potable_water:

Investing in a gas hot water heater in 2023 might be a little late depending were you live. Gas will probably get more expensive over time while with electrical energy there luckily is many sources including renewable ones (some you can even put on your own roof :sunny:).

There is also (on demand) hot water heaters without storage (like said I think they are not compatible with heat pumps) and they have the same “advantages” as the on demand gas water heaters :fire:

I’ve not seen on demand style instant electric here in AU myself yet but I understand they are popular in other countries.
One of the hard questions here where I am in South Australia is predicting the energy costs of gas and electricity into the lifespan of a new water heater, electricity has been going up slowly and steadily since supply privatisation decades ago, but gas seems to have eclipsed that in a rush now.
Yep I have solar PV so it’s likely that heat pumped electric is the way to go and use HA to bias it to heat during high solar output, but I’d like to prove that mathematically, but it’s not so easy to do that…

Is it? To my knowledge Australia uses a lot of renewable energies (specially photovoltaic) which is probably the cheapest source of energy available on planet earth. The sun will continue to shine no matter what. :sunny:

On the other hand gas actually needs a lot of energy to “harvest” and doesn’t count as a renewable energy source. :fuelpump:

For now you could just compare the price for 1 kWh of gas and electrical energy (and just assume they have the same efficiency). I guess that electrical energy is cheaper today and will probably also be in the future. :flying_saucer:

On the other and you have already PV on your roof (or elsewhere) which you can (or should) use and hot water just makes totally sense. Your hot water tank will/can essentially work as a battery (or energy storage). Having this combined with a heat pump will even “multiply” the energy you put into heating the water (like “invest” 1kWh and get hot water for 3/4kWh “out”). This is virtually free energy :twisted_rightwards_arrows: :zap:

No idea if Australia is exploiting fossil resources like gas, coal, oil and stuff (probably) but even if I would rather choose a clean energy source instead even if it would be more expensive (I very much doubt that). :wink:

No current data yet, but I’ve been using the 3rd unused transformer of a Shelly 3EM to monitor my electric hot water heater usage in preparation for an eventual replacement when it fails (it’s an 18 year old tank!) My online research suggests that the heat pump models are by far the most energy efficient.

Unless cost is an issue I think replacing any older gas appliance with another gas appliance doesn’t make sense. I recently had an HVAC tech tell me that Trane has advised that they will no longer produce any gas fired furnaces after 2030, and Trane has committed to becoming net-zero by 2050. Trane also recently completed testing of a high efficiency residential heat pump at -23° F (the DOE sustainability requirement is -20° F.)

I was also trying to figure out how to compare the efficiency/cost of my instant gas system to a heatpump, as I now have solar, and would love to remove gas all together (and my existing heater is over 15yrs and is starting to show its age).

I used chatgpt and some very rough approximations to help me realise I should be able to run a heat pump almost free with my solar.

  • I sourced my 4 previous quarterly to establish approximate daily gas usage.

  • my daily gas usage was X units, which they mentioned somewhere iirc was equivalent to ~3.6MJ per unit, or ~1kWh

  • Then asked ChatGPT to approximate how much water was heated (from say, 20 to 50c) in a day if I used X units / Joules / kWh or whatever from an instant gas heater. Which gave me approximately Y litres

  • Then I asked how many kWh this would use to heat with a resistive electric storage heater if I used the same Y litres in a day. This was roughly in line with the amount of energy the gas used, so I figured I was in the ballpark. Gas was always ‘more efficient’ for heating because ‘per kW’ of energy costs us around half what electricity would have.

  • Then asked how much energy a heat pump would use instead. and this was 25-30% of the energy as the gas/resistive.

I am now just trying to find something reasonably prices in my area, and hoping to find something on these forums with HA integrations.