Air-source heat pumps - are they good/crap?

[clockworks]

Coming back to this, now that I've had prices to replace the dodgy oil tank, and to switch to ASHP.

Quick recap:

West Cornwall, 1960's 2 bed detached bungalow (originally 1000 sq ft habitable) with a late 1990's dormer conversion (2 small bedrooms and a shower room). Last EPC was a "C" - cavity insulation, double glazing, loft insulation that could do with topping up a bit more in places.

No mains gas, so oil heating. Oil tank was basically condemned by the chap who serviced the boiler. No leaks, but the start of some surface cracking (UV damage?). Worcester 15kw system boiler is about 25 years old. Working OK though.

Replacing the oil tank like-for-like (and keeping quiet about it) is going to cost the best part of 2 grand.
Going for a fire-rated bunded tank (to satisfy current regs) would be £4k+.
Resiting a normal bunded plastic tank would possibly be a bit cheaper, but a real eyesore and a lot of digging.

Quote by a local ASHP installation company (personally recommended) who operate to the MCS scheme:

Mitsubishi 6kw ASHP
200litre unvented hot water tank
Installation, including removal of the existing vented immersion and header tank.

After the government grant, cost to me is £3600.
Survey said that my existing radiators are mostly fine, a couple might need uprating, best to see how it goes before replacing any.

The survey and calcs suggested heating needs of just over 5kw, heat loss of 56 watts per sq Mt, and annual 10,500 kwh for heat.


The calcs look reasonable. We get through around 900 litres of oil a year, so that's about 8000kwh equivalent.
I work from home, so temps are maintained throughout the day. The Evohome setup reduces consumption in unused rooms - lounge and 2 of the bedrooms are off during the day.

Looking at the numbers, if it achieves a COP of 2.5, averaged over the year, it'll cost the same to run as the current oil heating.
Up front, it'll cost about the same as just getting a new, compliant, oil tank.
I'll also get a much better hot water system - flow rate from the vented immersion tank is atrocious.

Seems like I should go for the ASHP?

[jonathan_roberts]

Is the 10500kw the calc for the heat pump or for gas? I can’t believe it would be that much.

[clockworks]

jonathan_roberts said:

Is the 10500kw the calc for the heat pump or for gas? I can’t believe it would be that much.

It appears to be the heat input requirement for the house to maintain target temps.

At COP of 3, that would need 3500kwh of electricity from the meter. Around £730 a year at the average unit cost on my tariff (Octopus Go) - not far off the cost of a year's worth of oil

[jonathan_roberts]

Right. Going on my experience, I’d be surprised if you use that much in a 2 bed bungalow.

Our house is just over 180m2 and for CH/HW is 4500kwh/year. I’m not sure of our heat loss though which I suspect to be minimal due modern insulation and windows and UFH.

[B'stard Child]

jonathan_roberts said:

Right. Going on my experience, I’d be surprised if you use that much in a 2 bed bungalow.

Our house is just over 180m2 and for CH/HW is 4500kwh/year. I’m not sure of our heat loss though which I suspect to be minimal due modern insulation and windows and UFH.

I reckon your house is much newer than a 60's bungalow - with much more insulation by design - it's quite hard to get to modern insulation stds in an older home whilst still living in it

Early 80's 4 bed detatched 112m2 over two floors CH/HW is now 7800 kWh per year

It was when we purchased it in 1991 25,000 kWh per year but it didn't have DG, CWI, LI, Condensing Gas Boiler and it did have a well vented suspended round floor which was incredibly leaky heat wise

Even just a couple of years ago it was 16,500 kWh a year for CH and HW

[B'stard Child]

clockworks said:

Coming back to this, now that I've had prices to replace the dodgy oil tank, and to switch to ASHP.

Quick recap:

West Cornwall, 1960's 2 bed detached bungalow (originally 1000 sq ft habitable) with a late 1990's dormer conversion (2 small bedrooms and a shower room). Last EPC was a "C" - cavity insulation, double glazing, loft insulation that could do with topping up a bit more in places.

No mains gas, so oil heating. Oil tank was basically condemned by the chap who serviced the boiler. No leaks, but the start of some surface cracking (UV damage?). Worcester 15kw system boiler is about 25 years old. Working OK though.

Replacing the oil tank like-for-like (and keeping quiet about it) is going to cost the best part of 2 grand.
Going for a fire-rated bunded tank (to satisfy current regs) would be £4k+.
Resiting a normal bunded plastic tank would possibly be a bit cheaper, but a real eyesore and a lot of digging.

Quote by a local ASHP installation company (personally recommended) who operate to the MCS scheme:

Mitsubishi 6kw ASHP
200litre unvented hot water tank
Installation, including removal of the existing vented immersion and header tank.

After the government grant, cost to me is £3600.
Survey said that my existing radiators are mostly fine, a couple might need uprating, best to see how it goes before replacing any.

The survey and calcs suggested heating needs of just over 5kw, heat loss of 56 watts per sq Mt, and annual 10,500 kwh for heat.


The calcs look reasonable. We get through around 900 litres of oil a year, so that's about 8000kwh equivalent.
I work from home, so temps are maintained throughout the day. The Evohome setup reduces consumption in unused rooms - lounge and 2 of the bedrooms are off during the day.

Looking at the numbers, if it achieves a COP of 2.5, averaged over the year, it'll cost the same to run as the current oil heating.
Up front, it'll cost about the same as just getting a new, compliant, oil tank.
I'll also get a much better hot water system - flow rate from the vented immersion tank is atrocious.

Seems like I should go for the ASHP?

I'd say yes it's a bit of a no brainer compared to oil tank replacement/relocation etc

Although your heatloss seems very good for the age of the house (despite the improvements) according to Heat Geek cheat table



From here (worth a read)

https://www.heatgeek.com/how-to-size-my-heat-pump-...

[jonathan_roberts]

B'stard Child said:

jonathan_roberts said:

Right. Going on my experience, I’d be surprised if you use that much in a 2 bed bungalow.

Our house is just over 180m2 and for CH/HW is 4500kwh/year. I’m not sure of our heat loss though which I suspect to be minimal due modern insulation and windows and UFH.

I reckon your house is much newer than a 60's bungalow - with much more insulation by design - it's quite hard to get to modern insulation stds in an older home whilst still living in it

Early 80's 4 bed detatched 112m2 over two floors CH/HW is now 7800 kWh per year

It was when we purchased it in 1991 25,000 kWh per year but it didn't have DG, CWI, LI, Condensing Gas Boiler and it did have a well vented suspended round floor which was incredibly leaky heat wise

Even just a couple of years ago it was 16,500 kWh a year for CH and HW

Yes hence I mentioned it. I cannot believe it makes that much difference though. But evidently it does. In any case the faff of replacing oil boiler and oil tank etc is greatly reduced with ashp

[clockworks]

Looking at that chart, 56 watts per sq metre seems about right for a 1960's build that was upgraded 25 yrars ago with cavity insulation, double glazing, and 2 layers of loft insulation in most areas?

There's one area that hasn't had extra insulation fitted since I've lived here, because the cold water tank makes access very tricky. I'll do that bit when the tank is removed. The rest had 100mm added to the original 75mm a few years ago.
I can't do anything with the dormer area, around 230 sq ft. I have to assume that it was insulated to the then current standards of the late 1990's.

[gfreeman]

clockworks said:

Coming back to this, now that I've had prices to replace the dodgy oil tank, and to switch to ASHP.

Replacing the oil tank like-for-like (and keeping quiet about it) is going to cost the best part of 2 grand.
Going for a fire-rated bunded tank (to satisfy current regs) would be £4k+.
Resiting a normal bunded plastic tank would possibly be a bit cheaper, but a real eyesore and a lot of digging.

Copied from another website - A bunded oil tank isn’t always necessary for a domestic property if it is storing less than 2,500 litres of fuel. Generally up to this level it really depends on the pollution risk as to whether you opt for a bunded tank. But there are also many cases in which a bunded oil tanks is a legal requirement, even for a domestic setting:

· Where oil spills could run into an open drain or a loose manhole cover

· Where the tank vent pipes cannot be seen when the tank’s being filled, for example because the delivery tanker is parked too far away

· Within 10 metres of coastal waters or inland fresh waters like rivers, ponds, lakes or streams

· Within 50 metres of a drinking water source, for example wells, boreholes or springs

· Where oil spills could run over hard ground and reach coastal waters, inland fresh waters or a drinking water source

· If your tank holds over 2,500 litres of oil

· Where the tank is supplying heating oil to a building other than a single family home eg a block of flats or a holiday house

· Where the tank is within an Environment Agency groundwater protection (SPZ) zone 1 (find out more at www.environment-agency.gov.uk)

· Where the tank is in close proximity to any other environmental hazard

[LooneyTunes]

gfreeman said:

clockworks said:

Coming back to this, now that I've had prices to replace the dodgy oil tank, and to switch to ASHP.

Replacing the oil tank like-for-like (and keeping quiet about it) is going to cost the best part of 2 grand.
Going for a fire-rated bunded tank (to satisfy current regs) would be £4k+.
Resiting a normal bunded plastic tank would possibly be a bit cheaper, but a real eyesore and a lot of digging.

Copied from another website - A bunded oil tank isn’t always necessary for a domestic property if it is storing less than 2,500 litres of fuel. Generally up to this level it really depends on the pollution risk as to whether you opt for a bunded tank. But there are also many cases in which a bunded oil tanks is a legal requirement, even for a domestic setting:

· Where oil spills could run into an open drain or a loose manhole cover

· Where the tank vent pipes cannot be seen when the tank’s being filled, for example because the delivery tanker is parked too far away

· Within 10 metres of coastal waters or inland fresh waters like rivers, ponds, lakes or streams

· Within 50 metres of a drinking water source, for example wells, boreholes or springs

· Where oil spills could run over hard ground and reach coastal waters, inland fresh waters or a drinking water source

· If your tank holds over 2,500 litres of oil

· Where the tank is supplying heating oil to a building other than a single family home eg a block of flats or a holiday house

· Where the tank is within an Environment Agency groundwater protection (SPZ) zone 1 (find out more at www.environment-agency.gov.uk)

· Where the tank is in close proximity to any other environmental hazard

It might not be a legal requirement, but if you installed a non-bundled tank and had a spill the conversation with your insurers (or bill for cleanup) might be quite interesting.

[Fonzey]

My oil tank was bricked in by a previous owner (to stop thieves I guess, as they also nailed carpet grippers to the top edge of the enclosure ). It does fill me with a bit of dread to be honest.

I check on it regularly, and I guess one benefit is that it's shielded from UV - but any maintenance on it would be chaos and any "emergency" maintenance would only be possible after ripping down a breezeblock enclosure.

[clockworks]

The existing tank is at the side of my house, up against the boundary. Originally a fence, but nextdoor extended right up to the boundary 20+ years ago, eaves overhanging the tank.
A like for like replacement wouldn't get "signed off", so no approved person would touch it.

A normal plastic tank would gave to go in the front or rear garden, as there's only 1.8 metres each side of the house. Do-able, but a proper eyesore.

Apparently an ASHP only needs to be a metre from the boundary, so it will fit at the side of the house against the garage wall. Oil boiler is in the garage, so that'll make the plumbing very easy.

[cptsideways]

Insulating a house to suit a heating system that's marginal is the wrong way to think about this.

If you insulated your existing house you could reduce your current energy consumption massively. The cost to keep your existing system is next to zero. Calculate the pay back time on that scenario.

The likes of solar vacuum tube water tank heating is largely ignored at 20% the cost and uses virtually zero electricity in the process. There is no reason it can't heat a tank of water for heating purposes, we just don't use it like that.

Our big old draughty Victorian is now a mostly warm non draughty place and we've reduced gas consumption by about half, payback time is minimal.

[OutInTheShed]

clockworks said:

jonathan_roberts said:

Is the 10500kw the calc for the heat pump or for gas? I can’t believe it would be that much.

It appears to be the heat input requirement for the house to maintain target temps.

At COP of 3, that would need 3500kwh of electricity from the meter. Around £730 a year at the average unit cost on my tariff (Octopus Go) - not far off the cost of a year's worth of oil

Is it valid to assume your average unit cost from a vehicle tariff will apply to your heating?

How quickly does your house cool down?

Can you heat the house during the cheap tariff hours, or will you mostly need heat at peak hours?

That's aside from my opinion that cheap night rate electricity won't stay cheap.

[clockworks]

OutInTheShed said:

Is it valid to assume your average unit cost from a vehicle tariff will apply to your heating?

How quickly does your house cool down?

Can you heat the house during the cheap tariff hours, or will you mostly need heat at peak hours?

That's aside from my opinion that cheap night rate electricity won't stay cheap.

Octopus Go cheap rate applies to the whole house.

I asked the chap who did the survey about running the system to maximise the overnight usage, and he said that it should be possible. When they come out to do the detailed site check, I'll find out more. Makes sense to at least heat the water overnight, which is what I currently do with the immersion heater (hot water isn't plumbed via the boiler).

Cheap rate electricity is cheap because there's a surplus at night. Better for the supplier/generator to shift some load and sell it cheap. I can't see that changing any time soon. E7 has been a thing for as long as I can remember. I just googled it, apparently since 1978.

[OutInTheShed]

Night rate electricity goes back further than 1978, my parents had it early 70s to my knowledge.
The cheap period has got shorter.
There's more and more people charging cars at night, there's increasing solar power, more people with batteries, talk of grid scale batteries etc.
The past may not be an exact guide to the future.

Houses vary a lot in the 'thermal time constant'.

My house is fairly well insulated, but made of lightweight materials.It cools noticeably after sunset, even though it doesn't take many watts to keep it warm.
My brother's house is moderately well insulated but has a concrete floor slab and some solid internal walls. It's much slower to heat and cool

My house, it's a complete waste of heat to heat it after we've gone to bed. My brother's house, it's best to take a long term view and you could heat the floor slab at night to keep you warm the next day.
Plus, what do you actually want? Personally, most of what we want is a warm lounge in the evening, and sometimes some heat on a Winter morning.

If you're running the heating around cheap tariffs rather than what you actually want, it can be inefficient.

Some friends of ours have a shiny new build house with heat pump, I'd like to think it's well insulated, but their bills are not particularly low. They are 'up country ' a bit though.
Water heating is a trivial amount, unless you are very wasteful with power showers.

The other thing is, at night, when power is cheap, your heat pump is trying to pump from cold night air, so you get less COP than in the day.

I think heat pumps will get cheaper, but then the handouts will disappear.
They ought to pay their way on standard tariffs. More so as gas and oil become less popular?

[clockworks]

OutInTheShed said:

Night rate electricity goes back further than 1978, my parents had it early 70s to my knowledge.
The cheap period has got shorter.
There's more and more people charging cars at night, there's increasing solar power, more people with batteries, talk of grid scale batteries etc.
The past may not be an exact guide to the future.

Houses vary a lot in the 'thermal time constant'.

My house is fairly well insulated, but made of lightweight materials.It cools noticeably after sunset, even though it doesn't take many watts to keep it warm.
My brother's house is moderately well insulated but has a concrete floor slab and some solid internal walls. It's much slower to heat and cool

My house, it's a complete waste of heat to heat it after we've gone to bed. My brother's house, it's best to take a long term view and you could heat the floor slab at night to keep you warm the next day.
Plus, what do you actually want? Personally, most of what we want is a warm lounge in the evening, and sometimes some heat on a Winter morning.

If you're running the heating around cheap tariffs rather than what you actually want, it can be inefficient.

Some friends of ours have a shiny new build house with heat pump, I'd like to think it's well insulated, but their bills are not particularly low. They are 'up country ' a bit though.
Water heating is a trivial amount, unless you are very wasteful with power showers.

The other thing is, at night, when power is cheap, your heat pump is trying to pump from cold night air, so you get less COP than in the day.

I think heat pumps will get cheaper, but then the handouts will disappear.
They ought to pay their way on standard tariffs. More so as gas and oil become less popular?

Could be it was called something else back in the day?

I had E7 and storage heaters in my last house. Longer cheap period, but both rates were higher (compared to the standard tariff).

Octopus have just increased the cheap rate Go period from 4 to 5 hours.
Home battery storage and selling back to the grid (or reducing daytime consumption) is doing the electricity generators a favour - saves them building their own storage and/or more generating capacity. I'm sure it will become less beneficial as more households do it though.

ASHP should be comparable in cost to oil or propane right now, but only if the COP is around 3.
Point taken about ASHP being less efficient at night though. Worth heating the water at night, as it'll last all day. Heating, probably just keep it ticking over at night.

My aim here isn't about trying to save money compared to oil, it's about future-proofing for a similar outlay as buying a new oil tank.

[caziques]

clockworks said:

Coming back to this, now that I've had prices to replace the dodgy oil tank, and to switch to ASHP.

Quick recap:

West Cornwall, 1960's 2 bed detached bungalow (originally 1000 sq ft habitable) with a late 1990's dormer conversion (2 small bedrooms and a shower room). Last EPC was a "C" - cavity insulation, double glazing, loft insulation that could do with topping up a bit more in places.

No mains gas, so oil heating. Oil tank was basically condemned by the chap who serviced the boiler. No leaks, but the start of some surface cracking (UV damage?). Worcester 15kw system boiler is about 25 years old. Working OK though.

Replacing the oil tank like-for-like (and keeping quiet about it) is going to cost the best part of 2 grand.
Going for a fire-rated bunded tank (to satisfy current regs) would be £4k+.
Resiting a normal bunded plastic tank would possibly be a bit cheaper, but a real eyesore and a lot of digging.

Quote by a local ASHP installation company (personally recommended) who operate to the MCS scheme:

Mitsubishi 6kw ASHP
200litre unvented hot water tank
Installation, including removal of the existing vented immersion and header tank.

After the government grant, cost to me is £3600.
Survey said that my existing radiators are mostly fine, a couple might need uprating, best to see how it goes before replacing any.

The survey and calcs suggested heating needs of just over 5kw, heat loss of 56 watts per sq Mt, and annual 10,500 kwh for heat.


The calcs look reasonable. We get through around 900 litres of oil a year, so that's about 8000kwh equivalent.
I work from home, so temps are maintained throughout the day. The Evohome setup reduces consumption in unused rooms - lounge and 2 of the bedrooms are off during the day.

Looking at the numbers, if it achieves a COP of 2.5, averaged over the year, it'll cost the same to run as the current oil heating.
Up front, it'll cost about the same as just getting a new, compliant, oil tank.
I'll also get a much better hot water system - flow rate from the vented immersion tank is atrocious.

Seems like I should go for the ASHP?

I'd be worried about the specification.

Presumably there are radiators involved, do you have 1/2" pipes?
How does the heat pump switch between the radiators and the hot water cylinder? Is there a coil in the cylinder?
What refrigerant?
A 6kW heat pump may be a bit on the small side for adverse conditions.

[Sheepshanks]

clockworks said:

I work from home, so temps are maintained throughout the day. The Evohome setup reduces consumption in unused rooms - lounge and 2 of the bedrooms are off during the day.

Are you thinking of continuing to have those rooms unheated if you had a heat pump? It might be a struggle to warm the lounge up so its usable in the evening.

[Ardennes92]

OutInTheShed said:

clockworks said:

jonathan_roberts said:

Is the 10500kw the calc for the heat pump or for gas? I can’t believe it would be that much.

It appears to be the heat input requirement for the house to maintain target temps.

At COP of 3, that would need 3500kwh of electricity from the meter. Around £730 a year at the average unit cost on my tariff (Octopus Go) - not far off the cost of a year's worth of oil

Is it valid to assume your average unit cost from a vehicle tariff will apply to your heating?

How quickly does your house cool down?

Can you heat the house during the cheap tariff hours, or will you mostly need heat at peak hours?

That's aside from my opinion that cheap night rate electricity won't stay cheap.

If cost allows, fit a large battery and charge that on the “cheap tariff” and use during the day? Add solar when cheap rates stop