Originaltwist

Forgive me for plugging my own ideas but this might do the job for you at a much lower cost. Basically it's a double radiator in a pair of kitchen cupboards with PC fans above. More info and picture on Originaltwist DIY fan-coil heater. Integrated into some storage cupboards with a nice shelf on top it will look good in a bedroom.

Have a look on the Henderson site .... industrial grade tracks etc ... all rated by Tarzan.

I don't suppose this is the answer but I had a similar problem on one of my systems... terrible flow remained after checking everything.... in the end it was the return and flow plumbed back to front on the pump so it was trying to flow backwards ....dooooh

Forgive me if this is not a useful contribution to the discussion. Would an integrated 'I' beam system - as above - be a good alternative? I've written more about it on my web site but it's just an idea and I'd welcome criticism from those on this forum who really know what they are talking about. Basically the idea is that instead of lugging up beams and slabs you just pour the whole thing on and leave the formers in situ as the finish.

The values on this chart vary from time to time but will, I hope, help clarify your strategy. So option 1/. A new gas boiler is cheap, makes lots of high grade heat and your valued radiators (and the pipes) will work as they do now. Option 2/. ASHP. The drop off in radiator performance might lead to regret. To get to high temperatures the heat pump COP will be lower than advertised and your running cost will be high. Option3/.??? Divert funds to some solar panels and run a mini-split alongside them - it's a lovely partnership and gives you a heat pump without messing with your pipes.. BTW, I love heat pumps ... just saying, don't rush in.

Can 28mm pipe convey 11kW at 35'? It's actually all down to flow and Dt. Having a play with my models... first - Flow. 22 litres per minute is 0.69 metres per second (26mm ID) which is reasonable for this example I trust (like 2 showers running). A pipe is just a very long tank so turning to the 'power to heat a tank' model you can see that for that flow to make 11kW a Dt of about 7 is required. So 35' to the pool and 28' back. So yes, it looks possible if that Dt can be reached and a good pool heat exchanger might help with that.

I get a few referrals from this site to my own - DIY fan-coil heater, energy costs compared etc - so I'm joining the fun here. I really appreciate the level of knowledge dispensed in such a friendly way and look forward to chatting with like minded folk.