I bought a Heat Pump

Reed_Richards

Cardew said:

...At the moment it is surely a 'no contest'.

However in the future things could change - either way

My installer reckoned the current ("RHI") subsidy is sufficient to make the cost of installing a heat pump (after subsidy) equivalent to the cost of installing an oil boiler.  And at current prices it's cheaper to run an oil boiler than an ASHP (unless you can achieve a better CoP than my system has, which you might if you had underfloor heating instead of radiators).  But if you are putting in a new "boiler" you will be looking for at least 10 years of working life and who knows what will happen to fuel prices over that time period.  As you say,  "in the future things could change - either way" so it's actually a very difficult decision if you are faced with it now.

When I was looking around I got quotes for an ASHP from three companies.  Two told me that the ASHP would save me money in running costs and one told me that there would not be much in it.  If you believe the quoted SCoP then it's actually a simple calculation to compare running costs and my calculation a year ago told me the third company was correct.  I went with that company and have no regrets whatsoever.   

shinytop

Cardew said:

Reed_Richards said:

  A Money Saving website would ideally compare the full life cost of your heating, not just the running cost.  This would include the cost of replacing the boiler (or whatever) periodically and other ancillary equipment you need (like an oil tank for oil). 

100% agree.

In existing houses, factors for full life comparison costs should include:

A. Running costs.

B. Replacement cost of a gas/oil CH boiler(if needed) and installation of a heat pump system. - taking into account subsidies for a heat pump.

C. Future repairs/replacements.

At the moment it is surely a 'no contest'.

However in the future things could change - either way

If choosing to reduce emissions were always purely an individual, personal financial decision, and people chose to have ASHPs, EVs, PV, etc. only on that basis, then we would never change.  

Thank goodness it's not like that.

Cardew

Reed_Richards said:

Cardew said:

...At the moment it is surely a 'no contest'.

However in the future things could change - either way

  I went with that company and have no regrets whatsoever.   

I have used your useful results over 12 months to re-inforce my argument that at present retro-fitted Heat Pumps are an expensive option both in terms of running costs and installation costs - even after subsidies.

I have passed no opinion on your individual circumstances and installation. If you are happy, that is all that matters.

Surely on an internet forum advice/opinions are for all readers and if anyone agrees or disagrees they are free to post.

Reed_Richards

Cardew said:

...Surely on an internet forum advice/opinions are for all readers and if anyone agrees or disagrees they are free to post.

Absolutely so @Cardew; I cannot fathom from what you quote why you think I believe otherwise.  My lack of regrets refers purely to my choice of  installer.  I don't regret my choice of an ASHP.  I'm a bit put out by the unforeseen rise in electricity prices but everyone using gas or electricity for heating is in the same boat. 

michaels

Reed_Richards said:

When I installed my ASHP in December 2020 I was able to buy electricity at 13p per kWh and I had paid an average of 45.2p per litre for my oil since we moved in in September 2018.  Now my electricity costs me 20.46p per kWh (up 57.5 %) whilst oil at 59p per litre is up 30.5% on my average price.  This has swung the balance in favour of heating oil.  Who knows what will happen in future.  You could envisage that gas prices will continue to rise, pushing up electricity prices and heating oil becomes the cheapest option!

I took advantage of a subsidy for installing a heat pump that gives you considerably more money back than the subsidy that replaces it after the old one ("RHI") finishes at the end of March 2022.  A Money Saving website would ideally compare the full life cost of your heating, not just the running cost.  This would include the cost of replacing the boiler (or whatever) periodically and other ancillary equipment you need (like an oil tank for oil).  Had I stuck with oil I would have needed a new tank costing over £1000 and I don't know how much more in labour.  

Sadly this is true - the current divergence of gas (and therefore leccy) and oil prices mean that actually if you were facing the full market price for your gas or electricity then oil would be by far the cheapest option right now - and will likely become so in April when the cap increases by at least 50%

shinytop

I don’t want to hijack @Reed_Richards thread but here are a few initial figures from another ASHP user.  Caveat - I don’t have a full year of data and I’ve been experimenting with different ways of running the system.  It might add a bit to the ASHP debate so here goes. 

In terms of my previous system’s energy used, there is no contest.  In November 2020 my storage heaters/immersion used 1913 kWh. In November 2021 my ASHP used 720kWh for heating and DHW.  Peak electricity is about 1.5 x E7 price so even with these raw numbers the ASHP, as expected, wins. 

It’s quite hard to compare the two systems though.  The storage heaters weren’t very controllable and you often over or undershoot what’s needed. I was also topping up with electric heaters and I used a lot of wood and coal but I can’t easily quantify that so I’ve ignored this.  However the ASHP is heating about 25% more area than the storage heaters did and it’s heating it more consistently and for longer.  It was also colder in November 2020 than in November 2021.  Using that extra information and the fairly detailed heat loss and performance models I have, I think my COP is around 4 for November, probably a bit more.  I’ll be able to confirm this when I get my MMSP monitoring working properly.   

It’s taken a lot of fiddling around with weather compensation curves and spreadsheets to get where I am.  I am running the system completely unlike I would a boiler.  I have my thermostats set to 30C and control the room temperature using flow temp/weather compensation only.  This keeps my house at 20-21C between (so far) -3C and 12C without any intervention.  The radiators are between 35C and 40C most of the time.  This won’t work for all houses or people but works for us.  It takes a big leap of faith to turn the thermostats up to the max and leave the heating on 24/7 but it works.  Having warm radiators instead of hot ones also takes a bit of getting used to. 

For info, my house is a 1990 bungalow of c.160m2. with decent insulation and double glazing.  Not a leaky old ruin but not a Passivhaus either. ASHP was a complete install; tank, radiators, the whole lot.  

An interesting number; at 5C ambient I can keep my whole house at 20-21C using about 1.5kW of electricity. I think that’s quite impressive. It’s still more expensive than gas though. BTW I’m no ASHP evangelist; to be honest if I could have had gas CH I probably would have.

EDIT - just received my first RHI payment of £401.17.  Thank you taxpayers   

Reed_Richards

I use a nighttime set-back on my heating controller.  For the sake of simplicity we'll say it is 21 C from 07:00 to 22:30 then 18 C overnight.  If the outside temperature is near 0 C it takes about 6 hours for the temperature to cool from 21 to 18 so the heat pump is off all that time.  That leaves 2.5 hour for my controller to get the temperature back up to 21 C in time for 07:00.  It will do this automatically if I set "Comfort Mode".  But to do this it has to make the water in my radiators hotter than is necessary to maintain a constant 21 C which means it will be running less efficiently.

Which is better for fuel economy, @shinytop's strategy of maintaining a constant internal temperature or mine?  With a conventional boiler I should win but with a heat pump it's not so obvious.  I'll have to try to read my heat pump meter after 22:30 and then (if I wake up in time) at 07:00 the following day to find out how much electricity that 2.5 hours of hard work uses. 
   

shinytop

I've seen calculations that show it can be better with an ASHP to keep it constant but I think it depends.  Your comfort mode will definitely use more power if it's boosting the flow temp.  I've experimented with just turning the ASHP off 12-5am; this drops the room temperature 2-3C.  I just let the house heat up slowly without any boosting in the morning; it takes a few hours but that's fine with us. 

This is running all night (blue) and of for 5 hours (red) in November/December.  There's not a lot in it.  
 

Reed_Richards

The truth is what I actually do is more complicated than my simple explanation.  I set back the room temperature by 3 C at 22:30 then up by 1 C in time for 07:00 and gradually up during the day until it arrives back at the base temperature (21 C) at 17:00.  I've been doing something like that for the past 24 years, ever since I had a programmable room thermostat and with whatever boiler.  It's what feels comfortable; I think because as the day progresses we get more sedentary and need it a bit warmer.  So in terms of heat demand that's probably very similar to @shinytop 's red dot data.

That's a very interesting chart, @shinytop ; I'm still getting my head around the trend line.  I suppose with a conventional boiler the power requirement would double from 11 C to 1 C ambient (because 2*(21-11) = 21-1 ) whereas with your heat pump arrangement it's nearer treble rather than double.

Meatballs

Reed_Richards said:

I use a nighttime set-back on my heating controller.  For the sake of simplicity we'll say it is 21 C from 07:00 to 22:30 then 18 C overnight.  If the outside temperature is near 0 C it takes about 6 hours for the temperature to cool from 21 to 18 so the heat pump is off all that time.  That leaves 2.5 hour for my controller to get the temperature back up to 21 C in time for 07:00.  It will do this automatically if I set "Comfort Mode".  But to do this it has to make the water in my radiators hotter than is necessary to maintain a constant 21 C which means it will be running less efficiently.

Which is better for fuel economy, @shinytop's strategy of maintaining a constant internal temperature or mine?  With a conventional boiler I should win but with a heat pump it's not so obvious.  I'll have to try to read my heat pump meter after 22:30 and then (if I wake up in time) at 07:00 the following day to find out how much electricity that 2.5 hours of hard work uses. 
   

8.5 hours (maybe less if the HP is actually cycling off for periods) at your efficient COP kWh

 vs

2.5 hours at your inefficient COP kWh

Almost certainly the 2.5 hours? 

If it's a 10kWh heater running at COP1 for 2.5 hours = 25kWh

If it's running at COP 3 for 8.5 Hours - 3.333*8.5 = 28.33kWh

Unlikely you will be down to COP1?