Notes from an eco house. (2025 Update)

With very high solar gain, how easy are they to cool in a hot summer? I assume that blinds/curtains are essential, but what about air-conditioning? I suppose the simplest thing would be to run the ASHP "in reverse", but isn't there some ban on doing that for subsidised installations?

Well naturally they will have to draw what curtains they have And open winbdows at night.

Mine does when the load is high, heating the air fryer etc. I would think 80W is realistic then but less when drawing the 150W base load here.

The pre-2020 RHI prevented an ASHP being installed that could be used for cooling (officially, there was usually a hidden jumper or something to turn it back on). But subsidies are only for retrofits - on a new build you wouldn't get them and are free to install what you want / could get past building regs.

A decent new build would have sufficient shading and/or overhangs so that solar gain isn't a problem in summer. Part O should cover it, although it only came in in 2022.

Theo

Yes but as long as the cylinder is not lossy (John R said his lost about 60W) you can heat it off peak at 100% efficiency for 7p/kWh and export during the day at 15p/kWh, losses of 1.5kWh (10,5p) in 24 hours compared with dhw on demand.

Yes I'm not knocking it, it just doesn't suit me. My daughter OTOH benefits greatly , runs a car for no net fuel cost and the surpluses offset her standing charge.

The new Octopus cozy tariff requires one to have a smart meter that switches the storage heater. Apart from that it would suit me.

The system is that every electricity supplier for those 30-minute slots will get paid the same amount per kWh as the costliest among them, so if an OCGT plant successfully bids at 100x ‘base rate’ then that’s what they all get paid. None of this ‘cheap renewables’ rubbish, they just take the profits while complaining publicly about the high price of gas.

It’s lunatic, for everyone but the suppliers.

Innit just.

Is that something they've told you? There's no mention of meter-based switching here: https://octopus.energy/smart/cosy-octopus/ It does say at: https://octopus.energy/policies/smart-tariffs-terms-and-condition/#cosyoctopus"2.7.3 To be eligible for the Cosy Octopus tariff, you must have a heat pump or compatible low carbon heating system installed and operational at the property which we supply. Compatible systems are determined at Octopus' sole discretion. If you sign up to our Cosy Octopus tariff but do not meet this eligibility criteria, we can place you on an alternative tariff that we consider is more appropriate for your circumstances. We will let you know if we do this and advise you of the rates and terms that apply to the alternative tariff."

so depends what a 'compatible low carbon heating system' means. A random storage heater might not count.

Theo

My mistake, the tariff I am referring to, for storage heating, is called snug, not cosy which is the one aimed at heat pump users.

Doesn't work for her address for some reason - asks me to input the figure (tried some variations around the defaults).

Some *very* peculiar readings around me. Mine's pretty much accurate, but some are from an educated guess wild underestimates - some are even negative.

My immediate neighbours use over 3 times the gas, and double the electric, to me. Says something about someone :-)

OK thanks, yes. I think an additional issue with older homes is damp, especially to the ground floor, where the building is constantly drying out due to partially failed DPMs. No evidence mind, just a guess.

My comment on transferring was made in trying to make your experience widely applicable - it does sound average(ish), but there's such a wide variety of homes . . .

All of that said, it's not too difficult to calculate heat loss, at least to ballpark figures.

I'll measure it under different loads. Bought myself one of these as an xmas present to self:

I understand that Octopus want to sell you power at a time they can buy it cheaper, but why are they *so* concerned with whether you're then going to use it for heat pumps, EVs, or growlamps?

Ah, I'd not come across that one. It seems like it's a variable time that's set by the meter, rather than the fixed times on Cosy.

Have you asked them if they'll install the right meter for you?

Probably that they give you discounts based on predicted usage. eg if you have an EV your usage might be a constant current draw in the nighttime, while a heatpump will tend to run more at dusk in winter when the temperature drops. They aren't too bothered if individual customers deviate from the model, but in aggregate they predict that X million customers' consumption will look like <this>, and price the tariff accordingly.

If they take on too many customers who don't fit the profile (eg those who use more energy in peak times) then it blows holes in their pricing model. By filtering on what you have it's a hurdle to prevent growlamp/etc users from jumping on those tariffs. They're also keen when they can tell your car/heating/etc when to fire up, rather than just having fixed periods.

Theo

It doesn't work for my own either. Maybe being on a smart tariff foils it, I don't know.

Tried a few houses I know and the numbers seem about right, but I wouldn't be able to verify with actual bills.

Negative could be if they're exporting solar?

I checked a house on a retirement estate. Don't know the occupants, but the usage was high as you might expect.

Yep, that's the plan. Just the crawling is such a PITA. I've invested in some Gapotape to make installation easier.

I think a big unknown is the pre-WWI houses - single skin brick, suspended wooden floors, designed to be heated with a big coal fire running constantly. Some decent internal wall insulation would likely help a lot there, but it's quite disruptive.

Indeed.

My ASHP installer's survey came in at 5kW, my own calcs at 8. So that's pretty average I think.

Theo

AIUI growlamps are mainly LED now.

No chance! They're big houses occupied by single state pension men.

snip

Yes, I recently completed the traditional building retrofit assessor course, and it's a minefield. You have to variously maintain ventilation, keep it all breathable, and have a regard to the enviromental integrity of whatever materials you use. And insulate it.

I've only got a little (HNC building modules) level of technical knowledge, but I think they overdo the porosity/ventilation thing. Seal the envelope with celotex and heat recovery ventilation - through wall by room if necessary. I've got a pile of books to get through on the subject . . .

Mine's about 10 (1910 semi).

Possibly the only accurate results are from those with a working smart meter. Some people will not bother with giving monthly readings to their utility companies

I think the numbers come from the same place as the 'your annual consumption is ...' on your bill, which must be calculated from actual bills and estimated readings if you don't have a smart meter.

Interestingly, someone with no smart meter in the middle of a switch had a 'your annual consumption' figure on their account even though the switch hadn't happened yet (no switch date set and no readings sent). So there must be some database that their old supplier is submitting the reading to that the new supplier and the comparison sites can find it out from.

Theo