Electric combi boilers / solar panels / eco heating solutions

Interesting, thanks for this intel.
I haven't done masses of research yet, but am desperate to get off the big smelly oil tank in the garden.

After PVs we will tackle the cavity wall insulation then see what is left for heating.

For context we have just bought a 1970s house that hasn't been touched since the day it was built and are trying to get our heads around how to bring it up to spec without over investing.

compromised performance if retrofit overlay/between joists

I'm not convinced given UFH is fundamentally more efficient than radiators (also surely the emitter volume of a rad is even worse?!).

Our bedroom being too warm is a worry, I'm not sure we'll need heating at all in our loft when we're done as we barely turn it on as it is, but it will be a separate zone so we'll be able to control it.

I definitely wouldn't want screed UFH in a bedroom, that'd be daft, but stepping onto a warm floor in the morning seems pretty comfortable to me...

stepping onto a warm floor in the morning seems pretty comfortable to me...

Carpets are pretty great at this.

We're having both 💅🏻

Straight to the golf club for you :D

I'm in London but my boiler, which is ~ 60 degrees, is on for a fair chunk of time in the winter.

Given that the heating is only on (set at 18) for 6-8 hours a day those chunks of 25-30% boiler on is pretty much representing the boiler being full on when we're home with the heating on (I don't have it on when I wfh during the day).

It might be that the heat pump can do something clever with efficiency at lower temps during the day so there is less of a jump necessary but I'm very much struggling to find much about using heat pumps in houses with smaller radiators and poor insulation.

Of course improving insulation and replacing radiators would be the ideal but then it becomes a massive job requiring pretty much the whole house to have work (and the biggest heat sink of big end of terrace wall is very difficult to insulate).

Ideally the heat pump would run continuously 24/7 and modulate its flow temperature, thus heating output, in response to outdoor temperature.

Providing the system is specified, installed and programmed correctly, with no buffers/low-loss headers/zoning etc and run in weather compensation mode, then it won’t be hard to achieve similar/lower running costs to gas, even with existing undersized rads.

Yes, but then you've got the cost of installation that's gonna take a huge time to pay if the running cost is just similar to gas.

I'd posted a HeatGeek quote I recently got in the heat pump thread. It was 20k once the grant is taken off, and would save me an approximate 8 quid a month. The main reason for this is it being an old house with solid brick walls, being relatively large, and some of the existing pipework being microbore.

In situations like this, heat pumps still don't make sense IMO. In a newer place with cavity walls and insulation, absolutely it'll make sense.

Generic question. Is it possible to fit a wet UFH system to ASHP specs (150mm spaced 15mm pipes) but run it off a gas boiler until we can afford an ASHP?

Of course. The manifold will mix the right temp for the UFH regardless of what's coming out the boiler. Really want 100mm spacing though, snail pattern.

Yes, UFH works diffnewt so doesn’t go to the same temps as a rad

£20K post-grant is absolute madness.

We paid £3.5K after BUS grant for a 7kW Vaillant system, with Vaillant tank, completely new plumbing and buried outdoor pipework. £1.2K worth of new rads on top, which were VAT-free as the installer purchased them for us as part of the ASHP install.

That was with an independent installer; friends and family who have had heat pumps installed have paid less via big energy companies for theirs, all in uninsulated Victorian houses, all working well with varying levels of rad upgrades.

This. Fat pipes, narrow spacing, big volume. When you eventually get ASHP installed, remove the blending valve and secondary pump from the manifold, as they’re unnecessary and hinder efficiency.

So everything after the manifold could happily stay out when we change from boiler to ASHP? Sweet.

@ectoplasmosis so a combi boiler system would require an extra pump to push sufficient volume through that pipe setup? Presumably the aim would be to run the boiler as low as possible to get condensing benefits.

Some modern boilers have strong enough pumps to do without, depending on the rest of the system, but most UFH kits come with them so might as well.

FWIW I have a pump on my system even though I have an ASHP. Can’t hurt to keep flow high.

I’ve also got a pump and mixing valve on my manifold, but that was only installed as the plumber fitting the UFH was different to the plumber piping up the ASHP, and the two didn’t chat to each other much.

I’m gonna get it removed when we can afford to; the pump inside the ASHP is more than enough to push water through the entire system, and the dumb mixing valve always allows some return water to mix with the inlet to the manifold so reduces efficiency. It’s only really meant to be there if your flow temps are too high for UFH, i.e. a boiler feeding rads that need 60deg, and UFH that needs 35deg.

Yeah we have no mixing valve but a pump that I’ve rigged to come on when it senses +25 degree flow

Thanks all, that's really useful. With regard to pipe layout, we'll probably need to used pre-routed chipboard floorboards for the pipes since the floor joists are too skinny to notch to take bends in the pipes between trays/spreader plates between the joists. Is there any way to create a snail arrangement using those chipboard floorboards (that anyone knows of)?

Added 10kWh to my battery array today. Doubling capacity.

Solar Together were doing a deal so it was only £1,900 installed.

Sets us up to be completely free from daytime grid usage throughout the year and maybe 90% independent once we swap to a heat pump next year.

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Nice. Mine hopefully should be commissioned by the end of the day. Waited bloody ages. Still missing a battery but will now have a 8.6kW array and will have 27kWh in storage eventually.

Need to look at Octopus tariffs again now. Poss Agile?

If you have an EV, intelligent Go is great. 7p overnight 11.30-5.30.

Battery more than enough to see me though the day.

This boils my piss, not that I live there anymore but having economy 7 and paying 20 something pence overnight is criminal, think it was 6p when I first moved there.

Nice!

Was this price just for an additional array of cells? How much did you pay for the initial 10kWh setup?

Was this price just for an additional array of cells?

Basically yes. They daisy chain the original 4 into the same BMS as they max at 8 battery modules per BMS.

The previous 10kWh was part of an install with solar in Jan. That was 18 panels, batteries, inverter and install for £12k and change.

Batteries by themselves are usually about £700 each so about £500 discount and free install although that's really only turning off the inverter, plugging them in and turning it back on but need the install certificate so you'd have to get a professional in to do it anyway.

None of the quotes I have received have been below 20k, this is for complete rip out of a mix oil/gas system, re-pipe, all news rads etc, some new rad placements plus a 12kw ASHP. Its a painful amount of money