New gas boiler vs air source heat pump (ASHP) - What's the best boiler replacement option for an integrated heating system?

Well, what you don’t see on this forum is another magic trick.

This place really is multi-purpose. Perhaps some of the members on the heat pump related trials can give you their thoughts. I’ll ask them to stop by when they get a chance.

Our heat pump setup isn't exactly conventional so I can't comment on all of your statements but…

Our heat pump isn't noisy.

None of the pipes in our house had to be replaced. It works quite happily with normal 15mm pipes.

You do need to have the system properly specified and installed. My experience is that gas boilers tend to be oversized to avoid people complaining that they aren't working properly. This means they aren't as efficient as they should be. You can't really do that with a heat pump. 

Yes, you might have to replace radiators but often people find that their existing radiators are already oversized. Or they can swap a single for a double which takes up no extra wall space.

There's no arguing about them being expensive, which is why the govt are using incentives to encourage people to fit them. Running costs will depend on each case but looking to the future, it's likely gas prices will increase as the govt moves the environmental and social obligations from electricity bills to gas bills.

Hi @eezytiger I have a heat pump !

I think changing to a heat pump depends on what system you will be replacing. 

I have a bungalow which had gas powered warm air heating installed in 1969, in fact it appeared that the building was constructed around the warm air unit. There is ducting in the loft and vents into the ceiling of each room. The unit was replaced (it took a lot of work getting it out) about 11 years ago with another similar unit. We’d got used to the noise and the constant seesawing of hot blasts then gradual cooling. We liked the fact that we didn’t have to accommodate any radiators and that the heat was almost instant; we switched it off at the thermostat every time we went out, it took 5 minutes to get the house warm again. Our hot water was from a cylinder heated by an immersion, which we had no idea of the tank water temperature so had it on for far longer than necessary.

That all changed last January when we joined the Zero Carbon Heating Trial ! 

We had 7 radiators installed, only one is a big boy: our living room which is L shaped (about 6.6 m x 5 m max), has a 2.4 m double radiator which is a bit of a talking point. The kitchen one is a vertical double, the 3 bedrooms ones are normal proportions also double. The bathroom and hall are small singles. We also have an electrically heated towel rail in the bathroom which is separate from the heat pump system. So although we thought we had nowhere to put radiators it turned out that we did…!! The heat pump is a split system, an outdoor unit with the fan, and an indoor unit which has more gubbins and the controller, in the loft. There is refrigerant flowing between the two units, which transfers the heat/energy (magic). Pipework from the indoor unit it 28mm, then graduating to 22mm, then to the 15mm through the ceiling to the radiators. Of course we already had the airing cupboard with the old cylinder. Our new one is much bigger so less storage space in there but a bit of Marie Kondo dealt with that. Our room thermostat also displays the hot water temperature, which we have at 45/50 deg C. 

So, to address your list: 

Buy the heat pump - well I have to admit it was all paid for on a government trial; it’s all being monitored with data sent to Big Brother somewhere (not that one !).

Have it installed - no getting around that. There was a lot of disruption though we never lost our heating as the warm air is all still intact, though switched off forever now, I hope. It was put in during January/February so if it’s a straight swap for a gas boiler I’d advise trying to get a summer date or stock up on thermal underwear first.

Immersion tank - it’s an unvented cylinder now so we have mains pressure for the shower which is a great improvement. 

Radiators and pipework - I think a lot of the trialists have used existing radiators and pipework, though I presume my setup is the optimum as it’s all new.

Visual appeal, space, noise - ours is by the bins which aren’t visually appealing either, but the cold blast of air from it is more of a problem for me ! I wouldn’t want it on the patio, though of course if it was warm enough to sit out the pump wouldn’t be running, except for hot water but that’s only for a short time. It’s quite a big lump but I feel it’s so clever heating the whole house from just fresh air that I’ve come to love it, well admire it at least…

Tepid - not at all ! It’s constant and warm. Our thermostat’s at 21/22 deg C during the day.

Cost and elec 6x price of gas - well its sooo much more efficient than our previous heating I’m not expecting to be spending much more, though I realise that it all might rocket up in the cold winter days. 

What I must add is the warm feeling I’m getting that I’m not burning gas any more, and having all that heat/pollution going up the flue. 

This chart shows how much gas in kWh our old system used last Jan to mid-March, compared to the kWh of Electricity since then (just for heating not hot water). As you can see the price looks much the same, notwithstanding the unknown price for the coming winter months:

I’ve just had a quick read through https://www.ovoenergy.com/guides/uk-gas-boiler-ban and there’s a button at the end to register interest in being a heat pump pioneer ! I’ve not clicked on it but if there’s another trial like the one I’m on then you may be in luck !!

@eezytiger Another great thing about the Zero Carbon Heating Trial was that before we signed up we had an energy survey done by a Retrofit surveyor. He produced a Whole House Plan which suggested what could be done to improve the house’s energy rating. It was rated at 53 E which is not really ideal for a heat pump (which presumably is what the trial is all about - will a heat pump be enough ??).

The Plan lists out all the things that we could do regarding insulation/window/doors/solar/etc with an indication of costs and payback times, and the improvement in energy rating. Installing the heat pump has brought us up 12 points, from 53 E to 65 D. Further improvements would be insulating the floor (3 points better but enormous upheaval), ventilation (no points but strongly advised), 4kWp solar panels (18 points better), etc.

It gives example prices too for external and internal wall insulation - prices seem high and we have cavity wall insulation anyway, though it may have ‘slumped’ ! As you have solid walls maybe it would be worth getting a price for that. If one day you did get a heat pump then any insulation you can add will definitely help keep the running cost down.

I don’ t know anything about radiators except that they do get full of sludge so getting them flushed out might make your gas heating more efficient.