Electric Heatpumps.

Andy C: 
. …. Should we go down the road of the USA with new houses having central air systems ducted to each room? Should be better and more efficient than trying to heat up water/floors through UFH and allows for cooling in those sweltering hot summers we get!

There are two goals with such a system. One is heating. The second is clean fresh air. They do conflict with each other some. Air circulating purely internally is best from a thermal point of view, but you need some way of (at least) extracting CO2 and adding O2. The easiest and least costly way of doing that is air exchange with the outside. There has to be some heat exchange at the interface. There are fairly straightforward ways of doing that, and I know what is claimed for them in the literature, but I am not at all sure that how it works out in practice is near how theory says it operates.

I don't see that ducted hot air is any more thermally efficient than other methods. Let's stick with heating. If your house has a general indoor temperature of X and the outside of Y < X, then your house is going to be radiating into the environment at a rate given essentially by Y-X plus the insulating qualities of the interface (walls + roof + ground under the house). Ducted heated air or underfloor heating or hot radiators or space heaters or whatever, that is a question of distribution and what occupants are most comfortable with, not of thermal efficiency. (I agree that comfort is the main factor for those who can afford their heating bills in the first place.)

Denis McMahon:

When we moved to Hampshire, in the mid-1980s, we saw ducted air heating installations in several houses, including in the one we eventually bought. ……..

There are some downsides to ducted air heating…… this system can be easily designed and built into a new house but adapting to an older house, …..is less easy and probably very expensive.

There are individual devices for individual rooms which exchange air with the outside, and which exchange heat during the air exchange. They are not large. The specs for one device I have been looking at are roughly 38cm^2 cover, sticking out 5cm into the room (you get a 35cm to 60cm hole in your outside wall). They claim 82% thermal efficiency through heat exchange, and you can get them to exchange 15 m^3/hr to 55 m^3/hr for the same wall space. They are not noisy – claimed 25dB at 30 m^3/hr.

You just have to find that 38 cm^2 patch per room outside wall. 

It solves both problems of course: heating and air exchange.

One often hears the USA criticised for being one of the world's biggest polluters, but I think the Americans are onto a good thing here. 

It is not just the US. HVAC knowledge spreads around the first world as fast as any engineering.

Andy C: 
. …. Should we go down the road of the USA with new houses having central air systems ducted to each room? Should be better and more efficient than trying to heat up water/floors through UFH and allows for cooling in those sweltering hot summers we get!

There are two goals with such a system. One is heating. The second is clean fresh air. They do conflict with each other some. Air circulating purely internally is best from a thermal point of view, but you need some way of (at least) extracting CO2 and adding O2. The easiest and least costly way of doing that is air exchange with the outside. There has to be some heat exchange at the interface. There are fairly straightforward ways of doing that, and I know what is claimed for them in the literature, but I am not at all sure that how it works out in practice is near how theory says it operates.

I don't see that ducted hot air is any more thermally efficient than other methods. Let's stick with heating. If your house has a general indoor temperature of X and the outside of Y < X, then your house is going to be radiating into the environment at a rate given essentially by Y-X plus the insulating qualities of the interface (walls + roof + ground under the house). Ducted heated air or underfloor heating or hot radiators or space heaters or whatever, that is a question of distribution and what occupants are most comfortable with, not of thermal efficiency. (I agree that comfort is the main factor for those who can afford their heating bills in the first place.)

Denis McMahon:

When we moved to Hampshire, in the mid-1980s, we saw ducted air heating installations in several houses, including in the one we eventually bought. ……..

There are some downsides to ducted air heating…… this system can be easily designed and built into a new house but adapting to an older house, …..is less easy and probably very expensive.

There are individual devices for individual rooms which exchange air with the outside, and which exchange heat during the air exchange. They are not large. The specs for one device I have been looking at are roughly 38cm^2 cover, sticking out 5cm into the room (you get a 35cm to 60cm hole in your outside wall). They claim 82% thermal efficiency through heat exchange, and you can get them to exchange 15 m^3/hr to 55 m^3/hr for the same wall space. They are not noisy – claimed 25dB at 30 m^3/hr.

You just have to find that 38 cm^2 patch per room outside wall. 

It solves both problems of course: heating and air exchange.

One often hears the USA criticised for being one of the world's biggest polluters, but I think the Americans are onto a good thing here. 

It is not just the US. HVAC knowledge spreads around the first world as fast as any engineering.