"We run our tiny 2.5kW heatpump"

Thanks for the detail, Rob. What type/model of heat pump is it?

Posted By: djhNo way is wet heating economical, as well as being a huge amount of faff

Posted By: djhI expect you know the costs of installing a wet heating system better than I do

Yes but ... only a short time ago we'd not touch bad old air heating, recognising the value of high-mass low temp radiation. It's quite a jump - I have been astonished, but it's liberating to witness the change of heart here.

I'm reading above people talking about a 30kWh battery having high discharge rates etc. (that's what I understood to be the intent?). The discharge rate surely is limited by the inverter rather than the batteries, usually groups of 5kWh units. Generally the inverters are 3 or 5kW units (rounded). I've had 3's and 5's fitted for clients, but not seen a higher inverters, though not really had the need. Covering the few minutes per day of a 10 or 12kW elect shower (above the 5kW inverter feed) didn't seem sensible, but maybe someone here knows more detail of very high output inverters that could cover that short term high demand, and the cost premium of that inverter? would be interesting to hear about that cost/saving trade-off.

Back to djh's question, if I still recall it - my experience of A-A quotes is that the typical domestic heat pump installers know that an A-W will be let's say £20k with rads, so they quote £10k for A-A (why not if they an get away with it). So I use commercial air-con installers for my A-A projects, who might (for want of a better term) not realise there's a killing to be made in the domestic HP market, and give a competitive quote, as if it were a commercial job, more like £3-£4k.

I'd suggest enquiring with commercial air-con installers, and see how you get on. Consider that they will also be set up for maintenance/repair, as their normal commercial clients (shop fridge sets etc) will need fast response and reliability. This is just what I've done, and seems to work for my clients.

Posted By: fostertomBlimey, young Dave, was it that long ago - pre heat pump?

Well prices have certainly come down, and availability has improved. The question is whether the improved efficiency (=lower running cost) balances the increased capital and maintenance costs.

Yes but ... only a short time ago we'd not touch bad old air heating, recognising the value of high-mass low temp radiation. It's quite a jump - I have been astonished, but it's liberating to witness the change of heart here.

I've been using air heating from the start (in fact I had a 'bad old' forced air system in my very first house, and that was noisy!). And I supplement the air heating with a radiant heater. As long as I can dissipate enough energy into the house overnight, it stays warm during the day.

@ GreenPadddy; Apologies its a 9kW hybrid inverter I seem to remember it cost about £1000. the 2 x 10kW batteries are currently about £2500 each. My install cost £7325 plus I paid about another £500 for interconnecting cables and earthing provision. I also built an outside, insulated, storage cupboard and re configured the AC supply side to reflect the new grid power outage provision that the system offered.

@djh - you asked about “ any specific products?” - over here in Sweden Daikin, Mitsubishi, Panasonic run forever :)

Come in on this discussion late as have been almost full time on sorting replacement for my Delios inverter that has failed. The main issue of delivering a lot of kW from a battery is a practical one of delivering a lot of DC kW at low voltage into a inverter that will convert the same kW at lower volts.
The DC cabling becomes costly using 50 even 70 mm2 cables plus the inverter size to deliver it. I have settled on a Victron Energy set up, their systems can deliver much higher current from a smaller size inverter using a facility called power assist. I do not fully understand it, if at all. I came across it as in preparing to receive the equipment I read the install manual where it recommended that the inverter supply should be fused at 100A more than most DNO supply fuses and wired with appropriate size cable. I thought I had made an almighty hen up but the Victron Community forum helped to explain that I can limit the amount the inverter can take within the software and my inverter supply is protected by a 32A fuse anyway. The spec says the inverter can output 129A with power assist, and handle 188A of battery discharge current. So if anyone looking for high outputs from batteries maybe Victron is something to look at. Comparing to what I had before I get UPS which I did not previously have and I would get a bit higher kW from the battery except the battery (10Kw BMZ) BMS limit is 5 max. I would have liked to have added to the battery size butI would have to make the current one redundant as it is not possible to mix batteries of different makes and even you want to increase the current size with the same make and model there is a time limit as the one in use ages and becomes non compatible. The Victron set up can accommodate a wide range of battery makes.

Posted By: revorconvert the same kW at lower volts.

There is an error there, I meant higher volts i.e going from 48VDC to 230V AC.

I am basically building a hybrid inverter from seperate modules I will post on here details of finished item in a few weeks! I hope!.

Thanks for that. Very useful video. I hadn't realised you can reverse a battery-to-AC inverter to charge the battery! Very clever.