Air to water heat pump systems

If you are looking at a air/water heat pump, then it is not designed to be switched on and off as needed. There are timers, but, these are meant to just reduce flow temperatures (max about 4C for rads) and not for room temps.
Not always required to change existing rads, but if you are taking out storage heaters then maybe a good idea in those areas. You could replace the storage units with fan coils, but these can be more expensive than rads.

Yes, I've got one and had it for nearly seven years and I'm very happy with it BUT if you are seriously considering one then make sure you know how they work and how to operate them. They do not work like a conventional system and getting it wrong will cost you a lot of money and you'll still be cold.

They are not suitable to just turn on and off, they work best when gently idling witha flow temperature of around 35 degrees C. For every degree above that it will cost another 2.5% or thereabouts on your leccy bill so you need radiators that are capable of working at low temperatures. Likewise you shouldn't turn it off overnight or during the day, just turn the stats down a couple of degrees as it will take a long time to reheat the place.

Our system will take a couple of days to get the house up to temperature from stone cold unless I tweak the temperature control.Once set up though we've got nice even heat throughout the bungalow.

You need to ensure that the whole system is designed properly and not just bung onto the end of the radiators that you've already got. We installed it in conjunction with an overlay underfloor wet system but an alternative is for fan convectors which are quite effective with low flow temperatures.

I've got some info on my set up if you want to PM me

You'd have to do some heat loss calculations to see if your radiators would be large enough bearing in mind the lower flow temperatures. It's also worth looking at your insulation as well to reduce the heat losses.

You can get heatpumps with all the "gubbins" in the outside unit, they are called monoblocs and the circulating water, which contains antifreeze flows through the outside unit.

A split system has the compressor unit outside and the refrigerant to water heat exchanger and other stuff inside. Ours is a split and the circulating pump is the same as that in a conventional boiler - not ever so noisy but certainly noticable. I doubt its any noisier than your existing LPG boiler.

You really would need to get a proper assessment to see if it's viable. Get several quotes though and make sure it all gets explained very thoroughly. You do need to compare system designs but hopefully they should all come to a similar conclusion regarding heat losses and pump sizing.

Heatpumps do work but the systems do need to be properly designed and installed. Those who just bung one on in place of a boiler and dont understand how they work or how to use them are those who end up with a system that doesn't perform well and can cost a lot to run especially if you have high flow temperatures and try to run it like a conventional system