[jamiegreen]

Does anyone know if they work in old houses?

We have a stone house built in ~1800. We have upgraded with insulation in the floors, walls ceiling, but of course it is still fairly draughty if it is windy.

It's damn expensive to heat, and have considered an air source heat pump, but always thought that it wasn't really a good idea for old houses.

[Jochim]

They often operate at much lower temperatures than gas central heating. In older houses especially this will often require much larger radiators and/or UFH.

From my research a couple of years ago:

Replacing gas central heating with air source heat pumps was a waste of money, they're more energy efficient but the cost worked out the same due to gas being so much cheaper. If you have rooftop solar and batteries already and are overproducing electricity it might be a viable choice but without those you'd be spending a lot of money replacing radiators for no financial benefit.

Ground source heatpumps offered a decent cost saving but were extremely expensive to install. You also need space available to sink them or a lot of lateral space if you want to save a fair bit on the install. Before the energy crisis my estimates for breaking even on installation costs were on the order of decades.

[jrochkind1]

> due to gas being so much cheaper.

I'm curious where you live. The OP suggested that gas and electricity prices vary a surprising amount throughout the US, and that gas is not usually cheaper than electricity, but is sometimes. They did suggest if you are in a place where gas is a lot cheaper than electricity, that might be the one thing to make heat pumps not cost effective, but that this was not typical.

I personally do not know much about this. (I don't even know how to know if my own gas is "cheaper" than electricity, since they are metered/measured in different units!)

[Jochim]

I'm in the UK. Our gas is metered in m^3 but our energy suppliers typically bill and advertise based on the converted kWh price. My current prices for electricity and gas are 33.76p/kWh and 10.28p/kWh respectively. That's after a government price cap has been applied without it it's 49.15p/kWh and 14.00p/kWh

Based on those prices a heat pump would need to have at least an efficiency of 3.28 (3.5 uncapped) just to break even. Given that the total cost of installation is in the range of £3k-40k there really needs to be a compelling reason to retrofit an existing house.

Some of this is due to the vagaries of the UK energy markets. The outcome is that we often end up paying renewable providers of electricity based on the cost set by gas powered stations. At the moment that price has been grossly inflated due to profiteering, we're far less reliant on imported gas than mainland Europe.

I'd like to note that the price savings and break even point have probably gotten better compared to when I last checked. If we go back to much warmer, happier times - like September 2020 - I was paying 15.999p/kWh and 2.915p/kWh for electricity and gas respectively. Prior to that it was 14.150p/kWh and 2.920p/kWh. At that point I believe an air source pump resulted in a net increase in my bill and a ground source heat pump would have taken around 30 years to pay off. I should probably recalculate when things have settled down a bit.

[jrochkind1]

Very interesting!

I wonder what leads to the gas/electricity price relationship being usually (but not always) inverted here in USA from UK. A good reminder that we think of these prices as being set by "the market", but there is so much policy and subsidy that actually effects them, probably in both/all countries.

Here my electricity is charged in kWh, but gas is charged in `therms`! I'm not sure if I can just convert one to the other to compare, or if differences in efficiency in various places matter, or what.

Let's see what I can figure out...

On my last bill, in Baltimore, Maryland, USA, from BGE. (I use standard BGE supply, I don't try to choose a different supplier on "the market", which is possible here in a confusing way)....

OMG looking at my bill, it's a mess. The first so many therms of gas were charged at a different rate than subsequent, then there's also a separate delivery charge per therm, then other fees... But let's just take my actual total bill and divide by therms... gives us $1.88813/therm... which I think google dimensional analysis tells me is $.0644/kWh for gas? Which is GBP 0.053/kWh for gas? Double what you are paying?

Electricity, doing the same with their crazy 5-part itemized bill and just dividing total charge by kWh used, I get $0.177/kWh. Which if I've done my numbers right is in fact 3x what I pay for gas, hm. GBP 0.15 -- same as you are paying?

I am confused and may not have done proper arithmatic.

OP suggests:

> In Connecticut, electricity costs a little more than $0.20 per kWh. Those same electrons cost $0.10 per kWh in Louisiana.

So my electricity rates are right smack dab in the middle there.

OP says of gas:

> In Florida the average price of residential natural gas is about $2. In Idaho it’s $0.65.

If those are therms, my gas rates are to the top end of that but within range: $1.80. Ok that makes sense.

Hm, so OP is suggesting at these prices heat pumps should still work out, which is not what you found...

[Jochim]

> which I think google dimensional analysis tells me is $.0644/kWh for gas? Which is GBP 0.053/kWh for gas? Double what you are paying?

You're paying about half of what I am for gas and electricity, almost 1/3 of the unsubsidised price. I'm paying GBP 0.1028/kWh for gas and electricity is GBP 0.3376/kWh. We usually list energy in pence(£1/100) as it's a bit easier to read.

It's interesting that you have additional consumption based supply charges. We have an additional daily "standing" charge that's independent of use. Currently those are GBP .2256/day(GBP 93.294/year) for gas and GBP 0.4669/day(GBP 170.4185) for electricity.

> Hm, so OP is suggesting at these prices heat pumps should still work out, which is not what you found...

The ratio between electricity/gas prices has reduced since I last looked into it. Based on 2020 energy prices in the UK a heat pump would have been more expensive to run unless it had a cold weather efficiency greater than 4.85. At the time this necessitated a much more expensive heat pump which is probably where the 10k came from.

If we look at the Energy Saving Trust's current projections[0]. Someone with a relatively new boiler would expect to save £115/year. My energy provider offers a relatively cheap installation package starting at ~£3k[2]. It would take 26 years to pay off the air source heat pump at that rate. Their projections based on April's price data.

Many people require extra insulation and larger radiators to offset the reduced output temperatures of a heat pump. Radiators add an additional £200-300 each (£500+ if you're splurging) and a 4 bedroom family home will have a minimum of 6, more likely 8. If you end up spending £5000 overall it'd take 43 years to recoup the cost of changing your system.

On the bright side! If you're on an older boiler you could pay it off in under 10 years and if you're unfortunate enough to be on resistive electric heating, as far too many people still are, you'd break even in just over 3.

If we look back to March 2022 when energy prices were still inflated, Which[1] estimated that replacing your combi-boiler with a heat pump would cost you an extra £80/year. Should energy prices stabilise we'd expect to see the savings offered by a heat pump decrease. Which also estimates a much higher installation cost at £7,000-13,000. At the top end it'd take 113 years to pay for itself based on energy costs at what appears to be the peak of the gas crisis.

Ground source heat pumps are more efficient but the time to pay it off is similarly dire. The Energy Saving Trust estimates £24k to install one in a horizontal trench[3]. If you don't have the space or don't want bury a grid of pipework across your entire garden they estimate closer to £49k. They estimate a saving of £195/year. You'll break even in 123 years.

The issue with them is that they're a large capital investment that doesn't result in equally large cost savings. Until gas prices rise much closer to that of electricity, heat pumps will either cost more to run or will take longer than their expected lifespan to pay for themselves.

[0] https://energysavingtrust.org.uk/advice/air-source-heat-pump...

[1] https://www.which.co.uk/reviews/ground-and-air-source-heat-p...

[2] https://octopus.energy/get-a-heat-pump/#heat%20pump%20cost

[3] https://energysavingtrust.org.uk/advice/ground-source-heat-p...

[jrochkind1]

> You're paying about half of what I am for gas and electricity, almost 1/3 of the unsubsidised price

Ah, maybe that explains it.

And that matches my assumptions about US vs UK and EU -- US makes energy really cheap for consumers.

That could explain the OP, the cost-benefit might make more sense with US energy prices? Or is that right, should it be the opposite? The OP seemed to know what they were talking about, do you think they were wrong? I'm figuring they were right for US prices but maybe not UK.

> It's interesting that you have additional consumption based supply charges.

So it's complicated, and has to do also with the fact that my state in the USA, Maryland, has a complicated "market choice" thing where you can choose your "energy supplier" from a number of different companies with different complicated rate structures (most of which float in some way, and change month to month). But of course you still get the gas and electricity through the same pipes and wires. So you still pay the traditional legacy companies for "distribution" to pay for the infrastructure, while (if you choose) paying different companies for "supply". then there are various other fees and taxes (some based on usage) on my bill that I have no idea what they are.

My impression is that the "supply choice" thing is all a neoliberal scam. The price structures are super confusing, and a LOT of people, especially poorer people who can't afford it, get really taken for a ride. Often there's a cheap "teaser" rate, then the rates balloon to something hypothetically "market-based" but who really knows where the numbers on your bill come from. I have stuck with the traditional/legacy supplier myself.

At least once a week people knock on my door (in a not very wealthy neighborhood), salespeople trying to get me to switch my energy supply. Except they don't say that, they usually are very misleading about what they are selling, trying to imply (or outright lying and saying) that they are from the government or the traditional utility company, or are here to "check that you've done things right on your energy bill" -- they never have written materials to leave with you or a brochure, just a patter. Which only reinforces my belief that it's just a giant market for scamming people. (I think the salespeople themselves often don't really know what's going on, they're young people desperate for work recruited for commission-based door-to-door and being scammed themselves!)

So USA -- cheap subsidized energy prices, but a system still set up to screw poor people and enrich scammy corporations (and screw the environment).

[dazc]

I lived in such a house once and it was permanently cold, even with heating left on all day. In this instance the problem wasn't just the draughts but also the fact that it was connected to the old standard sized radiators that never got hot, they were always just above tepid, at best.

The landlord will happily bore you senseless about how much money he's saved though.

[MonkeyMalarky]

There's no reason why it won't work, its just another (more efficient) source of heat.

[Jochim]

It might work theoretically but that doesn't mean it should be done in many cases. Where I live electricity is nearly 3x the price of gas. While some heat pumps can achieve this in certain conditions it eliminates most of the affordable options which raises the question of how long are you willing to wait before a £10k-50k+ investment pays itself off?

They typically operate at lower output temperatures than existing systems. For example, swapping out a gas boiler for a heat pump will often require replacing all the radiators with much larger ones as well.

IIRC they're also less responsive. You might find yourself keeping the house at 18-20c all day rather than turning off rooms you aren't using. The effect is that you use more energy than you would have otherwise.

[MonkeyMalarky]

Right, it is decision that depends more on the economics of where you live and your usage than the age or construction of your house. Where I live, gas is not an option and there are subsidies to change over to electric and off of heating oil.