@springswood

We have two Daikin single split A2A systems, 3.5kW in the living room and 2.5kW in the main bedroom. This is in a 4-bed detached, 1970s house, with as much retrofit insulation as we could practically do. The whole house heat loss is around 6-6.5kW. We also have gas central heating.

The Daikin units (FTXM25A/R and FTXM35A/R) both modulate down to 800W output and around 125W minimum input. They have a SCOP of 5.2 on heating, which was achieved over the last heating season.

All through the heating season, we used the 3.5kW unit in the living room to put a steady supply of heat into the house on cheap rate overnight electric. This was very effective and cost less than 2p per kWh of useful heat. Compared to gas prices from Oct 1st at say 90% boiler efficiency works out at 8.8p per kWh, so the A2A costs less than 25% the price of gas for overnight heating. In autumn and spring, we were often able to cover all our heating requirements by also running both A2A units at a light load during the day (off solar/battery) without needing the gas CH to come on at all. The units are easily powerful enough, the issue is one of spreading the heat around sufficiently evenly. With less heat loss from the house in autumn and spring, it seemed there was more time for the warmth to spread around and just using the A2A was fine. However, once we got into cold winter days, the kitchen ended up not being warm enough as did the bathroom and one of the bedrooms, and we let the gas CH take over during the day to even the temperatures out. Year to date, our gas consumption, also used for hot water and cooking, is down from 14400 to 8400 units, due to using the A2A.

In summer, the A2A was fantastic at dealing with the heat waves. With 34C outside temperatures for hours on end, our whole house was easily maintained at 23-25C with the occasional help of an extra fan to push the cool air along the upstairs corridor towards the other bedrooms.

One suggestion would be to get A2A units in only the places where they are most needed, perhaps just two indoor locations as we have done. You'll need a multi-split (one outdoor unit) to avoid the need for planning permission (2 outdoor units are permitted development on detached properties, 1 otherwise). If you keep your gas CH, then you have the best of both worlds, cheap heating via A2A whenever you can and gas when you need extra and for the hot water. That way you have cooling in summer and redundancy in your heating system. If the boiler packs up at some point, you can still heat the house well enough.

A more comprehensive solution would be to look at something like a Daikin Multi+ system. This is a single outdoor unit, 6.8kW or 8.6kW on heating, that can be connected to 3 or 4 indoor units, and also provides hot water. If you went down that route and got rid of your gas boiler at the same time, then you would be eligible for the £2500 BUS grant for replacing a gas boiler with an A2A system that can cover both he space heating and the hot water requirements of your house. You could also do away with your gas supply altogether and save on the annual standing charge.

Note, with multi-splits, you don't need the outdoor unit to match the total output of the indoor units, for example a 6.8kW outdoor unit would be perfectly fine with 3x 2.5kW indoor units.

I've mentioned Daikin systems, only because I have Daikin A2A in my house and I am very happy with it.