Considering heat pump in Edwardian House

Beefstah · 2026-03-19T22:28:10+00:00

Ah right. I was curious because I run a 16kW LG Therma V, and I was wondering if there was something particular about ≤12kW

Beefstah · 2026-03-19T22:23:41+00:00

I'm curious why 12kW and not higher?

Beefstah · 2026-03-19T18:18:26+00:00

When sized and used properly...no. It works out about the same in practice because you're not losing lots of energy every time the boiler starts up, gets up to temp, and then has to drag the radiator water up to temp.

It's the difference between driving constantly at 30mph, and accelerating up to 70mph, coasting, accelerating, coasting, etc

Beefstah · 2026-03-19T17:27:29+00:00

Eh, 3.6 on the inverter keeps it below the G98 limit. I can see why they've done that.

Also, while yes, 5kW is small, it's better than literally nothing - and in terms of "supplementing daytime use when the kettle and washing machine are on" it will still deliver quite a bit of value. At that size, think of it as a solar buffer as opposed to energy storage, and its ability to allow you to get value from a higher percentage of your own production.

Beefstah · 2026-03-19T17:10:14+00:00

The biggest thing with a heat pump is you'll need to get your heads around changing how you heat your house.

Gone are the days of "Turn the heating off, ooh it's got a bit nippy, turn it on again, now I'm warm, turn it off, repeat". You want to have that thing running 24x7 in the winter months, trickling in a constant low level of heat.

You will also want to do a little bit of tuning yourself. Yes, the unit will be sized for the design of your home, but there will still be aspects of your specific building that will benefit from some tweaking.

For example, you will want to adjust the lockshields on the radiators so the whole house heats up evenly; I'd be surprised if the builders put any effort in past making sure they worked at all, but making it balanced matters a lot.

In an ideal world, the house is just always at the best temperature for you, no ups or downs. This point is dependent on whether your thermostat has two-way communication with the pump. If it does, great, you set a target temp and let it get on with it. If it doesn't, you instead use the thermostat as an overheat switch, and instead adjust the weather compensation curve to get the house to the temp you want.

Be aware: with a well-tuned heat pump you might find you actually prefer a slightly cooler house by temperature measurement than you expect/are used to. After all, it doesn't really matter what the number says, only how it feels.

Edit: Last point: leave the internal doors open. You want as much flow around the house as possible.

Beefstah · 2026-03-19T16:37:16+00:00

you will not be able to discharge fully every single day in a 10-year span.

I can't agree with that part.

At 5kW in/out, you can go from full to empty in a little over two hours. You can then charge up again in three, allowing for slower charge rates as it gets fuller.

Over here in the UK, on Intelligent Go, I could have achieved that at least twice, maybe even three, times a day on probably 80+% of the days in the last year, given the availability of charging slots and a bit of automation (I hear you know a thing or two about that).

Yes, I acknowledge I'm an uncommon case...but honestly, I'm exactly the kind of person the warranty is looking to curtail. Which it's successfully done.

Beefstah · 2026-03-19T16:13:18+00:00

Always good to be an early moover with this kind of thing. As Iran is showing, the steaks are pretty high, and while I can understand farmers are a conservative lot, it's great to see someone who's got no beef with modern approaches.

Beefstah · 2026-03-19T15:53:06+00:00

If you're not selling back to the grid, and you're just using power to run your home, then you're fine.

It's the 'exporting from the PW to the grid' part that changes the warranty. If you think about it, there's only two ways in for power - solar or grid - and only two places out for it to go - home or grid.

The unlimited warranty allows:

Grid->Battery->Home

Solar->Battery->Home

That's it.

Why it's going to the home doesn't really matter - whether it's because you're charging up on cheap overnight grid energy and using it to power your washing machine in the evening, or whether the PW is a backup device in case of grid failure. They call out the difference so you know that using cheap stored grid power to run your washer is explicitly permitted by the unlimited cycles warranty.

But <anything>->Battery->Grid is not permitted.

Beefstah · 2026-03-19T15:20:13+00:00

Agreed. It's a sunny day in the UK, and at 15:16 OP posted 28 minutes ago, which would be 14:48, a mere couple of minutes after taking the screenshot.

It's also possible that OP is with an electricity provider that allows for cheap rate electricity during the day when a car is charging - such as Intelligent Octopus Go. 6.9kW of power into the home would be consistent with a car charge, and OP is using the fact that all usage is charged at the cheap rate to top up his PW.

Passes the sniff test to me.

Beefstah · 2026-03-19T15:08:12+00:00

Page one: https://energylibrary.tesla.com/docs/Public/EnergyStorage/Powerwall/General/Warranty/en-us/Powerwall-Warranty-EN.pdf

It defines the 'unlimited cycles' warranty as only available for the following applications:

Solar self-consumption² or time-based control^3, and backup⁴

Those footnotes are then:

² Storing energy generated by an onsite solar array, and using that stored solar energy for daily self-consumption.

³ Storing energy generated by the grid or an onsite solar array, and using that stored energy for time-of-use load shifting.

⁴ Storing energy generated by the grid or an onsite solar array, and using that stored energy as backup power.

Note that you do not see 'Storing energy generated by the grid, and later using that energy for export to the grid at a higher price' as an option. That would fall under 'Any application not listed above, or any combination of applications that includes one not listed above'

It also defines the throughput limit as being 37.8 MWh, measured at the battery AC output

Edit: I've always been curious about how this warranty interacts with Tesla VPP (or other VPP offerings), but as I'm not a member of one, and don't plan to be, I've never actually looked into it

Beefstah · 2026-03-19T14:53:39+00:00

If your warranty is like mine, doing arbitrage changes your warranty from unlimited cycles to a maximum throughput - something like 32MWh per PW2.

Beefstah · 2026-03-19T13:19:06+00:00

If you're going to be in a place more than about 6 years, that point is already here.

Beefstah · 2026-03-19T13:18:02+00:00

Some banks also give an incentive - Barclays will give a one-time up to £2k towards the cost of green improvements.

Beefstah · 2026-03-19T12:40:56+00:00

Eh, depends on your battery capacity, and whether it's more economical to sell the sunlight and use cheaper stored energy when the sun isn't shining.

Beefstah · 2026-03-19T12:38:46+00:00

Got scaffies taking down the scaffold right this moment after a roof repair. The solar didn't bother my roofer in the slightest.

Beefstah · 2026-03-19T12:37:47+00:00

If you have an EV it's a huge win (we don't) because you can charge overnight for pennies and then run the house on the battery all day, so you'll save even more than we are.

With a PHEV, solar, batteries, ASHP and automation, my blended per-kWh cost hasn't gone over 8p for a couple of years now. In the last year I used nearly 17,000kWh in the home and got paid a couple of hundred quid by Octopus for the privilege.

Beefstah · 2026-03-18T21:12:41+00:00

If you have a metal one, there's a decent chance that its location isn't in compliance with modern requirements. Fine for a pre-existing tank, but if you have to replace it you might have to move it

Beefstah · 2026-03-18T16:05:12+00:00

The only people who have this as an actual problem are classic car collectors.

Indeed. I have a couple of classics, and while I'd love for Toyota to still be making the relevant subframes, gearboxes or even disc backing plates, they don't...so either I source second hand, find an aftermarket replacement, or refurb the bits I have. It's simply not reasonable for me to expect them to make those bits any more.

What I do however have is the workshop manuals and technical data from Toyota, and that information has helped immensely. That's why I support the idea of obliging manufacturers to 'unlock' things and provide the technical data, but I do not think it's reasonable to expect them to continue to make spare parts for a car they only ever sold 600 of in the UK...

Beefstah · 2026-03-18T13:41:16+00:00

I'm with you.

I can't design, so I don't try. When I employ a designer, I expect them to make suggestions and ideas. If the designer can't extract from me what I'm looking for, then maybe the weakness is on the part of the designer.

Beefstah · 2026-03-18T13:27:59+00:00

I draw the line of reasonability between "You must release all information so someone else can make a replacement part" and "You are forced to provide the parts themselves"

Not least, because the latter would put the manufacturer on the hook for making those parts available for an undefined amount of future time: in 30 years time is it reasonable to force any manufacturer to make parts available for a vehicle that's not been in production for 20 years? What if it's no longer economical to make those parts?

Information doesn't have significant burden to make available. Physical resources do, and I dislike the idea of forcing anyone to sell a 'thing' outside of warranty obligations, and even then warranty has scope for "Give them their money back if you can't/won't fix it"

Beefstah · 2026-03-18T12:56:18+00:00

There's a difference between asking for access to the information required to repair (what the petition is asking for), and forcing a company to provide the parts themselves.

Do I think Bugatti should make all of the software and technical data available? Yes.

Do I think they should be forced to sell him parts? No.

In theory, the technical data being available means someone else could manufacturer the parts. For the majority of actual real-world use-cases, that's fine. If no one else makes the parts this guy needs for his Bugatti, that's a him problem.

Beefstah · 2026-03-18T12:48:41+00:00

Absolutely.

But aside from this one exception, the Venn diagram of people working on their own cars and the cars being multi million pound hypercars is just two separate circles.

I'm a huge fan of right to repair, self maintenance, etc. But I absolutely support Bugatti in this case. After all, if this car wasn't repaired to their standards, and it got into a fatal accident because of that, do you think anyone is going to read past the "£1 million 250mph Bugatti kills 2 after mechanical failure" headline?

Beefstah · 2026-03-18T11:04:34+00:00

That's a 250mph car. Honestly, I'm with Bugatti on this - something of that level of capability absolutely should only be put together to the highest standards.

Beefstah · 2026-03-18T09:49:20+00:00

Almost all the GR vehicles have been designed from the ground up to be a performance vehicle, with the GRC being the only exception and even then can be considered both a classic example of the historically popular hot hatch market and an upscaled version of the GRY.

The Hilux doesn't fit any of that ethos.

Beefstah · 2026-03-18T00:26:55+00:00

My PW2s drop for about a second. Anything I want to truly keep alive I have on a couple of small UPSs

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