Air source heat pump vs gas heating? 28 March 2022 at 6:10AM in Green & ethical MoneySaving 19 replies 666 views

waqasahmed

So

Electric heating is 100% efficient, which may not be as true for gas given efficiency losses in the pipes

https://www.edfenergy.com/heating/advice/electric-vs-gas-heating-whats-best#:~:text=So, is electric or gas,use is turned into heat.

Heat pumps I believe typically have a COP of 3. With this in mind, would an ASHP reduce energy bills for heating if it's currently a well insulated house with gas heating ? Or would they actually go up? 

Would I basically need to rip out the boiler too? 

QrizB

waqasahmed said:

Heat pumps I believe typically have a COP of 3. With this in mind, would an ASHP reduce energy bills for heating if it's currently a well insulated house with gas heating ? Or would they actually go up?

If you read @Reed_Richards thread, you'll see that he's recently replaced his oil (not gas) boiler with an ASHP and his bills have remained roughly the same (possibly a little higher).

Mains gas is generally cheaper than oil, even with the imminent price increase, so it seems unlikely that an ASHP would save money if used to replace a gas boiler. I would expect your bills to go up.

Would I basically need to rip out the boiler too?

I can't see how that question relates to the rest of your post. If you want a gas boiler, keep it. If you don't want it, remove it.

mickyduck55

Depends on the rest of your "systems".. I have solar and batteries and have been using my Air to Air AC /ASHP .. certainly saving me money but only because my electricity is inexpensive.
If its a stand alone ASHP as above probably not 

Exiled_Tyke

I was talking at the weekend to someone who has replaced his gas boiler with an ASHP. On the whole he's pretty happy but was surprised how poorly it performed on the coldest winter days and fears that it won't be able to cope with a harsh winter.    I don't think the case is yet strong enough for most households.   

arty688

I have a ASHP but I put it in when I built the house so it was designed for it. The issue with most houses is the heating system has been designed high water temps . So you may also need to replace all your radiators and maybe pipework. Also I would say from people I know everyone has changed to a combi boiler and ripped out the tank so they would probably need to find space for a tank to. So I don't think ASHPs are the answer for most .

Reed_Richards

My ASHP is rated to "cope" down to -15 C.  At such a low temperature I think the CoP will be very poor or I could retain the normal CoP but set the temperature inside the house to ~11 C and use my multi-fuel stove to supplement the heating. 

Most gas and oil boilers are over-rated with regards to providing the necessary heating so might be able to cope better during a harsh winter.  But my installer told me that during a severe cold spell his ASHP kept going when his neighbours' external oil boilers froze and stopped working.  And although we have cold spells sometimes, I don't think we have had a harsh winter since the 1960s.       

Reed_Richards

The trouble with an air-to-water heat pump is that you have to extract heat from the outside air and use it to heat water to 35 to 50 C in order to heat a room to 21 C.  With an air-to-air heat pump you take the outside air and heat it to the 21 C you need in the room.  The smaller temperature difference should give you a much better CoP.  

arty688

but you will also need something to heat water as well as the upheaval involved in a whole house A2A retrofit.

waqasahmed

mickyduck55 said:

Depends on the rest of your "systems".. I have solar and batteries and have been using my Air to Air AC /ASHP .. certainly saving me money but only because my electricity is inexpensive.
If its a stand alone ASHP as above probably not 

I intend on getting solar panels anyway tbh. If I have both, would I expect it to be cheaper than gas heating? 

Martyn1981

waqasahmed said:

mickyduck55 said:

Depends on the rest of your "systems".. I have solar and batteries and have been using my Air to Air AC /ASHP .. certainly saving me money but only because my electricity is inexpensive.
If its a stand alone ASHP as above probably not 

I intend on getting solar panels anyway tbh. If I have both, would I expect it to be cheaper than gas heating? 

Not quite what you asked, but like mickyduck55 I also have two AC units for additional heating. I was running one through the night on E7 in the winter, and since early March have had the GCH turned off, and just run one of the 3.5kW units through the day, on a mix of PV and import. By mid March it was almost entirely PV.

Assuming an export payment of about 5p/kWh for the excess solar generation, and a COP of 4 (air temps outside of peak winter are higher), that's a cost/kWh(t) of about 1.25p.

Exiled_Tyke

waqasahmed said:

mickyduck55 said:

Depends on the rest of your "systems".. I have solar and batteries and have been using my Air to Air AC /ASHP .. certainly saving me money but only because my electricity is inexpensive.
If its a stand alone ASHP as above probably not 

I intend on getting solar panels anyway tbh. If I have both, would I expect it to be cheaper than gas heating? 

I think that is very much 'how long is a piece of string' type question. There are so many variables to consider e.g. are you at home during the day?  Do bear in mind that solar performs at its best at the wrong time of day and the wrong time of year for most people's heating requirements.  My friend I mentioned above said it's costing him in winter but that's not his primary reason for doing it.