Are Heat pumps worth it

[deuce22]

I'm wondering whether to install an ASHP and would like to get some feedback from others on whether these are actually worth it.

 

I have a 350m2 property over 3 floors and was planning to use underfloor heating on each floor. I've read quite a lot and have noticed that although they are a greener choice, they are not as efficient as gas and in some cases ridiculously expensive. A heating engineer that fits these have told me to install a heat only boiler and cylinder or a combo storage boiler.

 

What are your opinions about this?

 

Thanks.

[PeterW]

1 minute ago, deuce22 said:

A heating engineer that fits these have told me to install a heat only boiler and cylinder or a combo storage boiler.

No.1… get a new heating engineer as the last suggestion is not for a 350m² house ..!!

 

They cost of the heat pump is broadly irrelevant - if you go full mainstream grants and badged installers you will get mainstream prices. The same units can be fitted by a competent plumber and electrician who can read and follow instructions.

 

The issue comes when you expect an ASHP to perform in the same way as a boiler and rads, which isn’t going to work as their efficiency points are different.

 

First place is a full heat loss calculation, then look at fabric investment in insulation and air tightness, and finally price the heat pump that fits the required heating load. 
 

Final thought is unlike a boiler, they are not a one trick pony and can cool so you can have a setup where you get floor cooling in the summer - that isn’t possible with a gas boiler !

[JohnMo]

As suggested get a better plumber.  Proper heat loss calc is important, not this is what normally do.

 

I have gas, so will give you an unbiased view on both.

 

A well insulated house with UFH throughout will have very low water flow temps, circa 26-29 on weather compensation. Limit the number of thermostats to one per floor and balance flows to match room temps needed.  Install a small buffer 50L.  This will act to give hydraulic separation from the pumps, as well perform a duty for the heat pump.

 

A decent heat pump should then give a CoP of around 5 for central heating at those flow temps and about 2-2.5 for DHW. So running costs will be lower, but if you have loads of thermostats and a low loss header, the efficiency will be lower.

 

If you have solar PV some of the running costs can be offset.

 

Gas, no cooling as mentioned.  Gas can be efficient, but I suspect in most cases they are badly installed to get a high efficiency, they also suffer from to many thermostats short cycling.

 

 

[billt]

21 minutes ago, deuce22 said:

I've read quite a lot and have noticed that although they are a greener choice, they are not as efficient as gas and in some cases ridiculously expensive. A heating engineer that fits these have told me to install a heat only boiler and cylinder or a combo storage boiler.

 

I don't know where you get the idea that they are less efficient than gas, properly designed and installed they should be 2.5-3.5 times more efficient than gas (that is energy out over energy in).

 

They may well be more expensive to run than gas but that depends on your utility prices and how well designed and installed the system is. Properly done and all things being equal, at the moment running costs should be broadly similar.

 

The heat pump itself will be a bit more expensive than a simple gas boiler, depending on size and manufacturer, but the reat of the system should be similar in cost. In the overall scheme of things the equipment expense is not that significant. When it comes to installers it's a different matter. At the moment there seem to be a few people following the double glazing,FIT and RHI examples; i.e. dodgy salesmen adding on the grant to the install costs and raking in extra profits.

 

I've been looking at heat pumps for some years and I'm now trying to get costs for replacing the gas boiler. The ball park prices I've been getting, although without a survey, seem to be about £9000 after the £5000 government grant. My calculations bring the material costs bought at retail including 20% VAT to about £7000 (including new cylinder and replacing 2 radiators). AIUI installers don't pay 20% VAT and should be getting trade discounts so their costs should be noticeably lower. If they're charging £15,000 it looks as if they're profiteering to me.

[ReedRichards]

In a large house you need to consider the length of your hot water pipe runs.  If your combi boiler is situated at one end of the house it will take a long time to get hot water out of taps at the other end.  A cylinder situated near the centre of the house would minimise the pipe run lengths.  If you want greater luxury, a cylinder supplying a hot water recirculation loop would give you the fastest hot water out of hot taps. 

[deuce22]

PeterW

That's what I was thinking, surely a small cylinder in one of those combo boilers isn't sufficient for 5 bathrooms.

 

JohnMo

I was thinking of installing solar if I go down the ASHP route.

 

billt

I've joined an ASHP group and there is a lot of unhappy people, one person is paying £20 per day to run as it wasn't set up properly.

 

ReedRichards

I was planning on installing a heating loop, but watched a video on youtube where the calculations were done and it cost a lot to have these running all year.

[nod]

Anyone who is thinking of installing a HP to save money on bills is going to be disappointed 

We have a job installing EWI and render on a local authority estate in Liverpool All have gone over to HPs At 0 cost to themselves There are three Clark’s of works overseeing the renovation 

So probably a better job than most private builds 

But all I here from the tenants is that there bills are higher and the heating is slow to heat up 

 

We will probably spend about 10 k on ours But need to factor in the cost of getting gas and a boiler to the plot 

Perhaps 7k So not a lot in it 

But we have accepted that running costs will be higher than our greenstar boiler 

Sellers need to be upfront about this 

In the same way as PV sellers are 😁

 

 

[Kelvin]

Two of the problems with ASHPs is that they are being installed in inappropriate houses and even when the house is appropriate they are often incorrectly specified, installed and configured.
 

Even when they are installed in an appropriate house and are correctly sized and installed the owners need to change the way they think about heating the house and hot water if they’ve come from traditional boilers.
 

I also think too many people run their houses far too warm although the energy price increase is fixing that. 
 

Gas boilers can also be incorrectly specified and installed of course. 

[nod]

8 minutes ago, Kelvin said:

Two of the problems with ASHPs is that they are being installed in inappropriate houses and even when the house is appropriate they are often incorrectly specified, installed and configured.
 

Even when they are installed in an appropriate house and are correctly sized and installed the owners need to change the way they think about heating the house and hot water if they’ve come from traditional boilers.
 

I also think too many people run their houses far too warm although the energy price increase is fixing that. 
 

Gas boilers can also be incorrectly specified and installed of course. 

Your right there 

I was talking to the installers foreman 

He said while these are the best they can be 

The houses arnt suitable With no insulation in the floors 

He also said Rads  arnt really suited to ASHPs 

UFH would be better with insulation 

But where do you stop There’s over a 100 k being spent on each property as it stands 

 

[Kelvin]

What is the mantra on here…fabric first! What you just explained is exactly the problem we have in the UK building industry where long term problems are built into properties at the outset. 

[JohnMo]

I'm really operating my gas boiler exactly the same as you should a heat pump.

 

Operating at very low temperature flow all the time and with weather compensation, and monitoring gas consumption and reheat times. Have 100mm concrete screed with UFH 0.09 u value for floor.

 

If you let things get too cold reheating time can be 24hrs.  As the heat input is closely matched to the heat loss.  You also use way more energy in that 24 hrs reheating, than you would over a couple of days at steady state, and very small night setback.  Also noticed it cost no more to have the whole house at a similar temperature, than it does with warm and cold rooms, maybe slightly less, as the flow temp can be lower.

 

So low flow temps, on for long periods, small nighttime set backs, no thermostats, if you hitting a thermostat your flow temp or DT across the radiator or floor loop is wrong and needs adjusting.

 

Lots of on/off thermostats, expecting quick heat up times, equals expensive to to run, true for oil, gas and heat pumps.

 

 

[ProDave]

1 hour ago, deuce22 said:

I've joined an ASHP group and there is a lot of unhappy people, one person is paying £20 per day to run as it wasn't set up properly.

At current prices, that would be about 65kWh per day or 2.7kW continuously.  It must be a big heat pump in a very poorly insulated house probably trying to drive high temperature radiators.

 

2 hours ago, deuce22 said:

 

I have a 350m2 property over 3 floors and was planning to use underfloor heating on each floor

Tell us about this property?  New build in progress?  Old house being refurbished? have you had any heat loss calculations done etc?

 

At the moment a heat pump is unlikely to deliver cheaper heating than a gas boiler, but in the right situation it will come very close.  They are a great benefit to people who don't have mains gas so the only other choices are LPG, Oil or solid fuel.  And don't forget you save the gas standing charge and cost of having gas connected if it is not already there.

 

[Kelvin]

When we first moved into our previous house it took some time for everyone to adjust to how the ASHP and UFH worked (and a bit of tinkering from me on flow temps at the mixer valves) The main thing was telling everyone to leave the thermostats alone! 

[SteamyTea]

As usual, there is misunderstandings around heat pumps.

Sized correctly, and run as intended, they are compatible to gas heating on cost.

 

With any system that uses UFH, plenty of insulation has to be fitted under the pipework. You would not put your radiators outside on the wall, so why would you, in effect, do the same with UFH.

[ReedRichards]

1 hour ago, deuce22 said:

ReedRichards

I was planning on installing a heating loop, but watched a video on youtube where the calculations were done and it cost a lot to have these running all year.

 

So that means you have to have a hot water cylinder; you can at least eliminate the option of a combi boiler.  I have a heating loop which I run for 5 minutes every waking hour.  This keeps the water out of the hot taps at least warm  and reduces the running cost.  The pipes in the loop are very well insulated but even so it's a bit of a luxury as I was traumatised by the overly long pipe runs before I refurbished the heating system.

 

So your choice is between a low temperature gas boiler (since you have UFH throughout) or a heat pump and with a hot water cylinder in either case.  I would have thought you could achieve a good enough COP with a heat pump and UFH to make the running cost competitive with that of a gas boiler.  At the very least you should design a system where the gas boiler could be easily replaced by a heat pump when it comes to the end of its life or if gas becomes prohibitively expensive.

[deuce22]

nod

Saving money must be one of the top reasons for people installing these. Why would you pay more for something at the start to then pay the same or possibly more to run? When I started this build 3 years ago, the plan was to install a heat only boiler with 300l cylinder, run off gas.

 

ProDave

It is a new build constructed from Nudura ICF, 150mm PIR in floor, warm/hybrid roof with 150mm PIR, 200mm mineral wool between rafters.

The boiler and cylinder I was going to install, was £3000 and this HE I mentioned, said he could do a HP for around £8/9000 and then get the £5000 grant. However I should then install PV to counter act the high running costs. This would add another £4/5000, so between £7/9000 for heat pump and PV and £3000 for gas + plus connection.

[ReedRichards]

I wonder if your HE is just touting for business?  I have both solar PV and a heat pump and the two are very ill-matched.  I have more solar electricity than I need in summer when I don't need heating and not nearly enough in winter to make much of a dent in the demand for electricity of my heat pump.  By all means get both but don't expect them to play nicely together.  

[PeterW]

10 hours ago, deuce22 said:

That's what I was thinking, surely a small cylinder in one of those combo boilers isn't sufficient for 5 bathrooms.

No it’s not but could be .. as it depends on demand and flow requirements for the bathrooms and concurrency etc 

 

But for that you need a plan, a spec and a set of calculations … not a bunch of guesswork and a heating engineer talking out of his ar$e… 

 

10 hours ago, deuce22 said:

I was planning on installing a heating loop, but watched a video on youtube where the calculations were done and it cost a lot to have these running all year.

It does - but you don’t run them permanently… and this is why you need a design and a spec and then decide what to do.

 

Start with a blank sheet of paper, work out your DHW requirements and then find your overall fabric heat loss and you stand a chance of getting a sensible design. 

[deuce22]

ReedRichards

So in your experience there's no benefit to installing solar to reduce bills from the HP? Have you got storage batteries as well?

 

PeterW

I didn't think it went on what my requirements are, I thought it was on the size of the house and how many bathrooms there are. It has 5 bathrooms, a utility room with sink and shower and kitchen. There is only myself, wife and child living there, but I have family that will stay multiple times per year. Our DHW requirements are not that much, but if a larger family moved here in the future, their requirements may be different.

I started this build 3 years ago and have about another year before it's all complete, the plan was to have it complete in 2 years. This won't be my final property as I have an opportunity to live on a small holding in 5 years time, so i will eventually be selling this.

[ProDave]

Re heat pumps and solar PV.

 

DON'T think of it as "PV powering the heat pump"  Think of it as "PV helping to power the whole ALL ELECTRIC house"

 

Like many on here, we are in the country with no mains gas, so for our present house, designed to be well insulated and air tight, an ASHP made sense. The only practical alternatives were LPG gas or oil.  I find is it easy to self use just about all our PV generated electricity just by time shifting big loads like washing machine etc to the middle of the day, and using excess otherwise unused PV to heat hot water via a diverter.

 

 

[ReedRichards]

1 hour ago, deuce22 said:

ReedRichards

So in your experience there's no benefit to installing solar to reduce bills from the HP? Have you got storage batteries as well?

 

I have a 4.8 kWp solar array and a 6.5 kWh storage battery.  Yesterday was sunny but the peak output from my array was about 3.4 kW.  My battery was fully charged by about 15:00 and fully discharged (15% charge) by 18:30.  And that's on a really good day, sunny days are rare in November and even rarer in December.

 

This is what my inverter reports; about 30% of my 25.6 kW of electricity usage was supplied by my solar panels on a really good day for solar power.    

Edited November 4, 2022 by ReedRichards

[SteamyTea]

20 minutes ago, ReedRichards said:

Yesterday was sunny but the peak output from my array was about 3.4 kW

That may be true, and quite good for time of year.

21 minutes ago, ReedRichards said:

This is what my inverter reports; about 30% of my 25.6 kW of electricity usage was supplied by my solar panels on a really good day for solar power.    

Not what your screenshot is showing.

 

kW is power, kWh is energy, they are not, on their own, interchangable.

[ReedRichards]

35 minutes ago, ReedRichards said:

about 30% of my 25.6 kWh of electricity usage was supplied by my solar panels on a really good day for solar power.    

 Oops yes @SteamyTea  , of course I meant to write 25.6 kWh.  It seems to be too late to edit the original but I have corrected the quote

[deuce22]

ProDave

I understand that the electric coming from solar will be used for anything electric in the house, not just on the HP, but I wouldn't bother installing PV if I wasn't installing a HP, so I'm combining them together.

 

ReedRichards

So how many KW over the year do you think you save through solar? 

[PeterW]

3 hours ago, deuce22 said:

didn't think it went on what my requirements are, I thought it was on the size of the house and how many bathrooms there are. It has 5 bathrooms, a utility room with sink and shower and kitchen.

It very much goes on DHW requirements, and flow rates etc are vital as are usage patterns. For example in your instance I would go for a pair of 180 litre slimline tanks in a tandem arrangement. That allows an extra volume when you need it but isn’t included in your standing heat losses.

 

There are a lot of moving parts in the design of this sort of system and one size doesn’t fit all - you need to start from base principles. I would also consider if you’re not going to keep this and want it saleable in 3-4 years then go with a single large tank (300 litre min), and a 28kW heat only boiler with a 100 litre buffer tank for the UFH assuming this is in solid/concrete flooring. Benefit of gas and a buffer is you can also run towel rails off it, and if you put an immersion in both DHW and buffer you can use them as dump loads for PV.