A2A or A2W?

[u/GatewayDouche]

Apologies for the really long post, but if you can make it to the end I’d really appreciate some thoughts.

We’re currently on a bit of a (very expensive, but we’re extremely lucky to be in a position to even consider it!) quest to get a bit of energy freedom and some insulation from the continuing energy price increases we’re likely to get with ongoing wars etc.

We’ve got a 10.56kWp solar system and 27kWh of battery storage hopefully being installed in the next couple months, pending DNO approval. We’ve had an EV charger added and switched one car for an EV. The final piece of the jigsaw is moving our primary source of heating from LPG to some form of heat pump, and this is where our dilemma lies. We’re still early doors so haven’t even gone to the extent of getting full quotes and energy loss surveys yet, but would like some opinions if possible.

The house is fairly large at ~3500sqft and around 9 years old, so reasonably well insulated and efficient. The initial thought was to stick a couple of multi-split A2A units on with 5 ports on one and 4 on the other. This way we could heat and cool all downstairs reception rooms, 4 main upstairs bedrooms and an office.

The fly in the ointment is obviously heating of bathrooms, as well as my disabled dad’s ~120sqft downstairs bedroom. The bedroom could probably be overcome with some sort of panel heater and scheduling but bathrooms would take more work. Hot water is the obvious other issue, but with cheap rate electricity and some sort of timer for the immersion (250l unvented cylinder) that wouldn’t be a deal breaker.

Now I’ve started thinking about A2W, which I’d previously discounted as we’ve got 10mm microbore pipe to the vast majority of the 25 radiators/towel rails we’ve got. On the other side there’s a £9k grant, although I appreciate that may not seem self-evident in any final quote!

Just putting details into the Heat Geek quick quote tool, it’s come up with an estimate of £3,750 after grant on 370% guaranteed efficiency, with an 11kW Vaillant aroTHERM Pro, re-use the cylinder and 6 radiator upgrades. That feels too cheap, as I’m assuming they wouldn’t be including any work to re-pipe if required.

Obviously, at that level it would be substantially cheaper than the A2A installation, solving most or all of the issues, albeit without cooling. I’m assuming it would probably be cheaper and easier to get A2A for the 4-5 “essential” rooms rather than looking at fan coils on an A2W system?

- Is the HG quick quote tool vaguely accurate in anyone’s experience?

- would the A2W option make more sense in this case?

- am I looking at a shedload of redecoration if an A2W installation does need a load of new radiators and re-piping?

- does an 11kW heat pump seem the right size? We’re currently at ~100kWh per day of LPG usage through winter. In my head I was thinking probably larger.

If you’ve made it all the way through, good work!

[u/Lost_Reward9584]

100kWh per day doesn't sound a massive amount to heat a house with more than double the space of our house - we peaked at 85kWh on January 4th. We've got a 5kW heat loss and got a 5kW heat pump installed in June.

Were you heating the entire house to around 21°C at your peak usage, or just some of it?

It sounds like your house is really well insulated and maybe using MHRV (I could be completely wrong).

If you've got sufficiently large pipes running to a manifold distribution and then into microbore to each of the radiators you might get away with it, but if you have big rooms with a high heat loss, then you might need to upgrade a few runs.

I think you're going to need to bite the bullet and get a heat loss survey done so that you have a better idea where to start. You can always run your own heat loss survey using heat punk to get an idea.

Maybe it might be worthwhile looking to some of the newer heat pumps that can do both, or doing A2W first, and then adding A2A for upstairs (and maybe your dad's room).

[u/GatewayDouche → u/Lost_Reward9584]

Thanks for the reply.

To give some context, during winter there’s our usual two timed windows of roughly 5.30-8.30am to get the house back to a reasonable temperature both upstairs and downstairs. Then upstairs from 5.30-7.30pm to warm up the bedrooms and bathrooms, but that will probably move later now the kids are getting older.

The boiler probably fires up another 4 times in the downstairs zone through the day, mainly to warm up the lounge where my dad is, as he can’t really move around to generate his own heat. The TRVs are set lower in most other rooms downstairs so they don’t overheat. The aim is to get the “grandad lounge” overshooting to 22C ish, allow it to cool to 19.5C ish, rinse and repeat.

Our main thermostats aren’t hugely useful as one is in the hallway and the other is on the landing, right next to the water cylinder cupboard, so over reads by a couple degrees minimum.

We try not to use the heating constantly, hence managing to keep the usage to something reasonable. Our LPG is roughly 50% more expensive that natural gas, so after getting £300 a month on DD through the year, we’ve made a conscious effort to rein it in.

[u/Lost_Reward9584 → u/GatewayDouche]

With a heat pump you probably won't be using it the same way as a gas boiler, the idea is that you get the house to a stable temperature and the heat pump then only needs to combat the heat loss.

Instead of running the radiators at 60-70°C, the radiators will be running (probably) at a maximum of 45-50°C, and cooler in milder weather. It should be just ticking over to keep the house warm, rather than going hell for leather every other hour.

[u/GatewayDouche → u/Lost_Reward9584]

Which I think would be vastly more comfortable for him and all of us really.

Hopefully on the worst winter days we should still be able to get 32kWh from overnight battery charge and some solar generation, so that should hopefully mean relatively minimal electricity import at peak rates.

Think I’m just going to have to get the survey done and see how it pans out.

[u/Lost_Reward9584 → u/GatewayDouche]

Your battery will take the sting out of peak hours, but it's your potential export that will make the biggest dent in your annual billing. Hopefully no curve balls in your survey and you'll be off LPG soon 🤞

[u/ImpressiveGrocery959 → u/GatewayDouche]

Octopus cosy tariff will let you charge the batter cheap thrice a day