Very interesting.  Aren't the efficiency numbers for boilers a bit like the COP figures for ASHPs, i.e. achieved under test conditions?  I think gas boilers are also more efficient at lower flow temps and can benefit from weather compensation, etc.  But gas is so cheap it's easier and cheaper just to crank it up when it gets cold.  Having said that I doubt you'll match gas costs with an ASHP at todays prices but maybe the difference isn't as much as is thought.

@kev-m I think everyone has zero idea of how efficient their boiler actually is - I didn't even think about it. My assumption, like anyone, would be that my boiler kwh of heat is what I needed to replace. However if your boiler is only 60% efficient in the real world, then you can assume your gas is 70% more expensive per unit of gas. This would totally change an ASHP calculation as it would make my gas cost for comparison 4.17p vs 2.5p or decrease my electricity demand before COP from 36000 to 20000. After a COP of 2.8 in the winter.

As an example my actual gas use in Jan this year was 5,000 kW, after the efficiency of the boiler and a COP of 2.8 the electricity demand to provide heat for the ASHP is 1,000 kW - 20% of the gas demand!!!! Given I have solar and batteries the ASHP should be cheaper. Especially as I can store power in the batteries at a lower rate.

I can do some more detailed maths, but I think the ASHP will be significantly cheaper than my current gas/elec. Time will tell on that, but I think with an increased battery system I can reduce my costs like for like from £125 on gas to £74 with tariffs, solar and batteries. Also I might be able to drop my current bill from £1265 to £578 with the Agile Go tariff and another 7kwh of batteries.

Hi batalto,

I read with interest about the efficiency of your gas boiler and had a look at the Installation and Servicing Manual, which quotes expected efficiency in the high 80's for both CH and DHW.

Do you have DHW set for pre-heat, which could be one reason for low efficiency? You could try switching it off for a period and see if it makes a difference.

What is the temperature settings for CH and DHW? They can be set individually.

If you are planning to get an ASHP, now would be a good time to try lowering the temperature setting for CH on your gas boiler. Initially you could try setting it at 40C, to see if your radiators/UFH etc. is of adequate size to operate with the lower temperature water produced by an ASHP. If the temperature within your home is maintained with CH at 40C then try 35C. I think the lowest that you could take the CH water is 30C.

Since you are planning to keep your gas boiler, if any of the above do not improve the efficiency then I would contact the manufacturer and seek their advice on why you are getting low efficiency readings.

Regards,

Derek.

@derek-m it's down at 50° for theb moment. Let's see what the wife says...

Still at 50° and no comments on the heating in the house especially having has a few cold days at zero. Next stop 45°

Hi Batalto,

When you get close to the point where your gas boiler is only just supplying the heat loss when it is cold outside, it will be firing up more frequently. Last night when the ambient air temperature went down to -1C, the water temperature requested by our controller was approximately 35C, and the boiler was firing up about every 20 minutes.

What is your efficiency reading now? Has it improved?

Regards,

Derek.

Still on 58%. No idea if that's the long term average and I'll need to reset it?! Can't find anything in manual that actually says.

As an aside we had to put on the AC today in our boys room as it was too hot. Our house has insane solar gain due to the insulation. Insulation has positives and negatives. At least the solar and batteries means it free

down at 45 for the last couple of days. No adverse impact on the house, no complaints about the temperature. We've had a few 0 evenings and nights and we are still using our 3 tog duvet. Overall pretty happy with the impact. Having radiators I was a little unsure about the lower temperature impact. I have a spreadsheet from Freedom Heat Pumps which includes radiator assessment and they were (apart from 2) classed as oversize for our needs.

Pump goes in next Friday and the boiler will be isolated. Given we are rolling into the spring/summer I expect we wont see the real acid test until late this year or even early next year. Jan and Feb seem to be the coldest months.

Good news @batalto, keep us all updated.

Global Energy Systems came out to our property and made amendments to our system (moved the filter, put in a bigger distribution pump and upgraded five radiators to Stelrad Compact K3s, and our system (touch wood) is now running amazingly well. We've posted a new video on our YouTube channel where we speak about all the changes. Please head over to our YouTube channel and check our Episode 9:

www.youtube.com/c/MyHomeFarm

@editor I am just reviewing COP and I looked up your ASHP, not easy as there isn't much literature. Mine will be a Midea 12kw unit and have a stated COP at -2/50 degrees of 368%. Mars I looked yours up and although I can't find exactly the same measure, the closest I could see was for -2/55 and it was around 2 (it wasn't a great graph). Does this tally with your real world experience? I am aware that a COP at -2 of 368% is pretty good, and it would further lower my costs. 

The Midea also have ambient temperature adjustment, which lowers the heating temperature to adjust for outside temps. Has anyone got this?

I think that is also called weather compensation curve. All modern ASHPs have this as an option. Or you can just set exit & return water temperature.