Quote Originally Posted by nonshinyfinish View Post
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Do you know for sure that you need underfloor heating? The internet is full of "certainties" about heat pumps – for example I read online (and was told by a plumber) that microbore pipework ruled out a heat pump and you'd have to replace it all. Guess what – our house is now heated by an air-source heat pump using our existing radiators complete with microbore pipes.

There is useful information out there if you can wade through the nonsense, but ultimately every house is different and the work that you do or don't need comes down to the heat-loss calculation for each room. Best thing you can do is contact some companies for quotes and find one that will do the heat-loss calculation up front for a small (or zero) fee. (Some will ask for big deposits etc before they do that.)
Microbore can certainly be made to work for heat pumps, but it requires a bit more design work and calculations to ensure it is correct. It may also require additional radiators added to a room to make it work (but you may have this with traditional pipework as well depending on the size of the radiators).

I would say it would be unusual for someone to find your situation where all the pipework and existing radiators were adequate to heat the house with a heat pump rather than a boiler. Having said that, it does happen especially if the initial calculations were done "rule of thumb" by a plumber or were done by an engineer who allowed plenty of leeway in their calculations. As a former design engineer it was pretty common for radiators to be 50% - 60% oversized for the space once allowances were made for the errors in calculations and then taking the next available size up to be on the safe side....

To answer a previous point, underfloor heating is not a requirement for air source heat pumps, but it does mean the efficiency of the system can be maximised. The main downside of using existing radiators and pipework is that as the heat pump is at its most efficient at lower temperatures, the radiators may not be able to put out enough heat to heat the room. You can compensate for this by increasing the temperature of the heat pump, but this leads to a drop in efficiency. Heat pump technology is developing all the time though and a lot of the modern heat pumps are really efficient even at 50 - 60 degrees rather than the 35 - 40 degrees of a few years ago.

In a new build I would definitely say that using underfloor heating with a heat pump would be a wise choice, the additional costs of underfloor heating installations are able to be swallowed up in the house build a bit and it does offer a nicer more comfortable heat in the house. However in a retrofit, I don't know that I would be going for underfloor heating, the cost and upheaval of it would be pretty significant when you could (worst case) just replace some radiators with larger ones or add an additional radiator or two to get the heat pump to work.

We've got an ASHP on our house (no mains gas up here) and have had no issues with it, but we are a new build with excellent insulation and underfloor heating throughout. Where people have had issues with heat pumps is where they have put them into old houses with radiators which were too small, potentially a heat pump that was too small and haven't improved the insulation levels of the house before fitting it. They then find that the heat pump is running at full load and higher temperatures for long periods just to try to keep the house warm and the bills start racking up.