apesort

Thanks for the reply, very useful points. Can I assume you don't find noise a big issue with them in bedrooms?

Thanks for the suggestion. I'd go for one of the main brands if I were to get one.

Anyone here using split A2A heat pumps for heating? Or in combination with an existing gas boiler or air to water heat pump. They seem tempting as a relatively simple solution, especially for Spring and Autumn heating loads. With the added benefit of cooling being an option for scorching weather. For example we've a 3 storey - 200m2 house. My non-detailed calcs would put the total winter heat demand around 13kW max. Our front hall, stairs and landing are all quite open plan up to the loft landing. The existing radiator in the hall does a lot of the work in heating the whole house. I've been looking at single 5kW to 7kW A2A systems, to install in just the hall (without considering other rooms at this stage). This would be 4-5 times the output of the hall radiator. My theory is that the hot air may circulate enough from this one device to sufficiently warm the whole house on Spring and Autumn days (or even cold June days like this morning!). We tend to have our bedrooms fairly cool anyway. For example this 6.0kW Daikin unit is about £1k - Even with "F-Gas" installation I'd imagine around £2k fully installed - Probably less than a days work for the installer and no need to touch the existing boiler or pipework. https://www.airconditioningworld.co.uk/daikin-ftxf60c-rxf60b-6-0kw- A full A2W upgrade of an existing hydronic system would of course be much more expensive and more disruptive as most of our radiators would have to be changed. I'm leaning towards getting a single A2A unit this year and testing how it performs this Autumn (and winter alongside gas). Then next year either go A2W heat pump or add additional A2A units to phase out gas. If we ended up with an air to water heat pump the Daikin in the hall could be additional, backup or just there in case we ever needed cooling. Am I missing any serious down-sides to my plan?

Thank you. May I ask why you say "drop no lower than 38 °C." Rather than say let the store run down to close to 21°C or whatever room temperature is ? It certainly looks like a 2000l tank would be much more worthwhile storage for the amount of energy that we're looking to store.

My understanding is that glycol isn't really necessary if you accept the risks. The ASHP will have a antifreeze function which will prevent freezing provided it has power. It would only freeze if there was a combination of a lengthy power cut combined with freezing weather. Good article about it here: https://renewableheatinghub.co.uk/do-air-source-heat-pumps-really-need-glycol

Good point, thanks. I guess in the ideal world we'd have battery capacity for all our energy needs inc. heating. This is the lower cost alternative for energy storage.

I'm investigating the pros and cons of having a large thermal store heated by an ASHP for home space heating. This year we'll have a decent amount of PV installed and will probably move our electricity supply to an overnight EV tariff. We're also planning on installing an ASHP (prob a 13kw unit) for space heating. We have the space in a utility room for a large thermal store for space heating. DHW is already provided separately by a combined heat-pump cylinder. I've been looking at simple, relatively-inexpensive thermal stores without coils or PHEs. For example: https://www.ebay.co.uk/itm/125057059348 - 1000l for £895. Which looks attractive for the price. https://www.ebay.co.uk/itm/114920430255 1500l for £1298 2000l for £1598 I'm thinking one of these in a "4 pipe" setup we could prioritise heating the thermal store during cheap off-peak "EV hours" and possibly also during the winter PV generating hours - In the winter we could then avoid using grid electricity for the ASHP during the morning and evening peak. I was thinking TS would be around 35-40 degrees to get the max COP from the ASHP. Radiators would be sized accordingly. But maybe it should be higher temp to maximise energy storage. As a very rough calculation: In an off-peak 4 hour window, the ASHP could potentially use 10kWh electricity to generate 30kWh of heat Say 1kWh of off-peak electricity is 20p cheaper than peak rate Ball-park £2 / day savings (not accounting for losses, running the heating circulation pump etc) Sounds worthwhile enough to consider further. Pros: Not massively more costly than a small buffer tank / volumiser. Allows shifting of the ASHP run times away from when it might otherwise be used. Cheaper than adding additional battery storage for off-peak or PV energy Heat loss from the store would be indoors, so not really lost. Cons: Not practical to fill the entire thermal store with glycol mix. I've read this isn't necessarily an issue, as the risk of a prolonged power cut during freezing weather is pretty small. Some say not to bother with glycol at all and accept the small risk of the ashp freezing. Has anyone else done similar? any considerations I'm missing? Many thanks