Are my current C/H Radiators good enough if I replace my old Gas Boiler for an ASHP?

As a brief answer without looking too much at the detail of what you have written is that it is unlikely. Radiators designed for gas boilers with a high flow temperature are too small to work with the lower temperatures coming out of heat pumps. In my ASHP survey 9 out of my 10 radiators would have to have been replaced. The only one that was ok was massively oversized compared to the room's heat loss for decorative reasons. I declined for a lot of reasons.

Peter 

Thank you Peter, like your home setup, I am thinking of keeping hold of my gas supply to give me, and any future occupant, the option of changing to a gas oven with separate induction electric hob in the kitchen plus a balanced flue gas fire in my lounge together with an ASHP, in the hope that this will give me, at least, a good background warmth throughout my modest family home whilst retaining my existing 9 convector style radiators. My wife and I are retired now and enjoy our EAPC e-bikes and so we are not really worried about petrol price escalation, though the change from undiluted unleaded petrol to E5 and now E10 has added more than 10% to my fuel consumption and so my harmful CO2 emissions, NOX etc have actually increased!

Our heat loss survey showed room by room heat requirements and current radiator output. I had begun to change some radiators over recent years and the outcome was that a further 6 needed changing out of 12 in the property. While the survey was done by the installation company, I used a draft in Heat Punk to adjust and check certain elements.

Although generally in the UK TRV’s have been the norm, for a heat pump, especially using weather dependent control, you would normally keep all TRV’s at maximum. As you are heating ‘low and slow’, additional restrictions can cause problems.

We also kept our gas supply for various purposes. We still have a gas hob but pipework remains for any other preference in heating.

Your mains supply will no doubt need upgrading to 80 amps but your DNO should do this as part of the process and the installer can request this as an LCT (Low Carbon Technology) upgrade.

Your insulation could be upgraded also. Additional loft insulation always helps, obviously double glazing is useful and although you don’t mention it, any insulation for a cavity wall (or insulation on any external wall).

For the grant, you will need an EPC and get an installer you’re happy with after any heat loss survey showed.

Although our installation was just over a year ago, it came in after the grant at around £2,700 which included surveys, new radiators, hot water cylinder and installation.

​@Cloudliner79 you’ve been starting some really interesting threads recently, it’s great that we’ve got a community that can help with this sort of thing! I’m looking forward to hearing about your progress with the installations. Keep us updated!

The issue with ASHP and TRVs is that even having a TRV fully open sometimes causes enough of a restriction to cause a flow problem so it tends to be no TRVs at all. I think it must deoend on how much of a margin you have left with a particular ASHP and the pipes you have already in the house. 

The advantage that you have with an A2AHP is that they are cheap enough to fit without the BUS grant so you don't have to conform to the (committee designed) MCS rules. My monoblock was £800 and a DIY fit and it replaces nearly 90% of my gas heating which is excellent as far as I'm concerned.

I'm also annoyed with the EPC I had done for the heat pump survey. Despite increasing the loft insulation to 200mm and changing some of my windows to triple glazing it barely changed the rating. Why? The new EPC rules now add requirements to have solar panels and an HP to get a significant improvement. It's not about how well you have insulated the house any more it now focuses on the tech. So you can have a poorly insulated house but so long as you've added some tech then you get a reasonable EPC rating. (Sorry, rant over)

Peter

Update: A multi-split A2A unit (heating/cooling at multiple locations) is £3-4k so still an option if you want to keep your gas boiler and want to play by your own rules. I quite like the multi-fuel flexibility and I have a woodburner as well but it plays a minor role.

​@Peter E thanks for this - I wasn’t aware that the EPC rating structure had been changed in this way. I can really imagine how frustrating this is if you have done a huge amount of work making a lower band house more efficient.