Michael_S

Agree with you re efficiency but it is more abut sleep comfort - I guess it doesn't take long to get used to warner nights as we do it every summer.

With the gas it is tempting to do a overnight setback and of course there is turning down to min heat during holidays and this is when the furthest rads take a while to warm up and then warm the room back up. That being an issue with the gas it is likely to be even more so with a heat pump. the issue not being total power output of the heat pump but how quickly that energy can be transferred to the the rads (whatever their size) due to the pipework constraint. Obviously with an HP I wouldn't use such a big set back.

How thick is your 'backbone/main loop' though - ours is rather long due to the house having bene extended and the whole upstairs is 15mm. The online tools suggest the most the upstairs rads could output is about 3.85kw at any sort of reasonable flow rate and that rate would only be achievable if you only take the total length of the circuit and ignore the corners and fittings.... On the other hand it does work with our gas weather comp boiler running at 55C at min outside temp but it takes a long time to warm up after a cool down in the furthest room, fortunately the gas boiler can modulate right down and keep the flow going rather than on/off..

Sorry, meant flow temp not flow rate - eg I know a conventional rad rated 2kw at 50C deltaT will output about 41% of that at 25C deltaT (45C Flow temp). How about a 2kw rated fan coil - us it the same?

For reference, I am currently replacing some rads in preparation for a heat pump, given restrictions in my circulating pipes it seems like I can't realistically go below a 45C flow rate for the coldest day so am sizing my rads accordingly so have not had to go up to triple panel or change sizes, rather just going from type 10/11/21 to 20/21/22. However the thought that if I were to use fan coils I could also use the unit for cooling is obviously quite tempting so there are 3 or 4 west facing rooms that get the hottest where fantails (if they have the right output and are not too ugly nor noisy) would be a tempting option.

Thanks for replying, beauty is in the eye of the beholder I guess, to me they look like the cheap rads/night store heaters you get in a bedsit so negative connotations. I found your other thread on fan coils and one question seemed to be about condensation if used for cooling. I was thinking that the forced air flow would tend to evaporate any attempt at condensation and so the problem would remain with the pipes not the rad itself? Finally it seems a bit harder to work out what the equivalent output in watts is for a fan coil for a given flow rate. It often seems hard to fathom out what deltaT they are using for their stated output and what adjustment factor should be used for a lower flow rate? Final finally, many of the units suggest that they only activate the fan if the flow rate is 35C or over - not much use for a heat pump running weather comp nor for cooling!

Thanks, new unit seems to be about 3k. Would we get enough back on the old one to cover the cost of getting someone to do the work? Either way seems a lot for a minor convenience gain.

So we have a set of doors, at one end we have a single opening door. This hinges on one end of the frame and latches to the bifold section that is made up of 4 pieces on a slide track fixed at the other end. It would be a big win for us if the single opening door could be at the other end of window, ie everything flipped. My guess is that the only way to do this would be a completely new set of doors but I would love to be told otherwise....

Fancoils seemed to be a lot more expensive and of course need a power supply nearby - and to me tend to look ugly... We decided a 45 flow temp was a sensible trade off between efficiency and rad size. I use da standard table of deltaT reduction factors, probably should have looked for rad brand specific ones but decided it was probably good enough. I have one rad that is claiming an improbably high BTU at deltaT 50 so I guess we will see.

Thanks James Interesting wording. It would appear that if you had previously heated your home with a heat pump but not had a grant, were the heat pump to break, if it were removed and you heated with resistance electric then you would be eligible.

WE have an above ground pool that we heat using a second hand heat pump. WE had an installer come to do a quote who suggested that this would mean we might not get the BUS grant and might have to apply for planning permission if we wanted a house heat pump. Anyone any experience of this? Thanks

If there were the option of another of boss lower in the tank, I would pump back into the bottom of the tank using convection to mix the tank as this allows you to maintain separation of hotter water at the top of the tank.

I have similar plans and have been strongly advised that roof mounting is likely to cause reverberation and that wall mounting is the safer option - I would also look into getting spring dampeners rather than just the standard rubber type mounts. Also consider whether the roof (or wall) is strong enough - our roof only had 4 inch joists. I assume you have stepped through the MCS permitted noise calcs with your set up and suggested unit noise power to 1m outside the nearest relevant neighbours window?

In a way the cost of the tank is only part of the story, not sure a new one would go through our loft hatch and even if it could it would then need to be plumbed. For a phe/pump solution I assume it is the useable hot water that needs to go through the phe, I wonder if the tank has suitable bosses?

So tank is at 30C, HP sends out water at 36C expecting it to return at 31C but instead it returns at 34C as the coil is too small. I would assume that it then either gets confused (thermostat says current temp is 30C so why is return so warm or perhaps it sees return at 34C and increases flow to 39C? But basically it needs to either reduce output (modulate down) or accept a bigger difference between the flow temp and the tank temp. One issue with the PHE+Pump solution is that you don't maintain stratification so well - at present I suspect we are still getting hot water at the shower when a lot of the tank is full of 12C cold water from the inlet and the average temp is well below 45C. However I can't see why this is not the preferred option over a tank replacement.