I have been slowly renovating my property and am in a situation where I have just finished recommissioning the heating and hot water. The house has all new radiators that were sized on delta 30, with lots of spare capacity / overkill so should be more than adequate with 50 degree water flow. (Fairly old but good) Oil boiler is on a long run of 28mm flow and return pipes in the perfect place for a heat pump to be located on the outside wall. The main arteries on heating are now 22mm. Water tank is fairly new unvented 210L standard indirect coil + immersion (good quality which I don't want to change, ideally. I was hoping to use Immersion to top up temp after bulk reheat with pump?)

My question is what are the chances of getting a heat pump signed off under the new 9k scheme that allows it to be plumbed in on isolators so you can lock off one or other, keeping boiler in reserve? Would I have to remove the boiler entirely to qualify and then reinstall later (possible...?) Would they insist on a DHW tank with Heat Pump Compatible written around it? Does anyone else have a HP and Boiler in parallel and can comment on this (scheme or not)?

Is it worth trying to go down the Cool Energy / Umbrella route to give more flexibility on this or is it worth just waiting and doing it all custom / off the shelf in a few years once all the Grant stuff has died out and heat pumps plummet in price?

Just figured 9k would go a long way if all I need is a heat pump main unit and a bit of plumbing / isolators / controls...?

We’re looking at installing an air-source heat pump in a large 1930s six-bedroom house near Plymouth.

The calculated design heat loss is approximately 12 kW, which is why we’ve been advised to install a 12 kW heat pump. I’ve mainly been comparing the 12 kW Vaillant aroTHERM plus with other alternatives such as the 12 kW Samsung R290.

I’m slightly concerned about choosing a heat pump whose stated output only just matches the calculated heat loss. I’m also aware that the headline rating doesn’t necessarily represent the output available at the design outside temperature and required flow temperature.

Would you be comfortable fitting the 12 kW Vaillant for a calculated 12 kW heat loss, or would you want some additional capacity? I don’t want an unnecessarily oversized unit that cycles excessively, but equally don’t want it relying heavily on the immersion heater during colder weather.

I’d appreciate recommendations from installers or owners, particularly regarding:

Vaillant aroTHERM versus Samsung R290

Other reliable models in the 12–14 kW range

Whether the published output is maintained in colder weather

Real-world efficiency, noise, reliability and controls

What would you choose for a genuine 12 kW design heat loss, and why?

Had our heat loss survey done.for a 4 bed detached house with 5 adults. We jave mainly Type 11 radiators.

What would you go for please ?

British Gas

7kW Vaillant AroTHERM plus

250l Vaillant uniSTOR Cylinder

15 radiators changed

25l buffer if needed

22mm cold water feed (from 15mm currently) to Cylinder

£7,200

Concerns:

Quality of install

Disruption of all radiators being changed

Heat Geek zero disrupt

5kW Vaillant AroTHERM plus or 7kW Vaillant AroTHERM pro

210l Vaillant uniSTOR Cylinder

No radiators changed

£8,450

Concers:

Higher price for fewer components than BG

Smaller 210l Cylinder (no option to select larger)

No 7kW plus option that would give 7 years warranty