Heating my hot water via a new Valiant Aerotherm plus Air to water system

shinytop

wittynamegoeshere said:

That's why I said "fat" ones, i.e. ones that are big enough to heat the room while being merely warm rather than hot.  I understand that you lose efficiency as you increase the water temperature.

We'd have underfloor in the main living rooms, radiators in the hall and bedrooms, where I don't want it to be hot anyway.  It's a bungalow, with concrete floors throughout.

I'm still at a very early stage of thinking about it!  Underfloor heating would be great, I'd be happy to wreck the lounge and dining kitchen to put it in as they need to be severely redeveloped anyway.  But the bedrooms are pretty good already, really the floor just needs screeding.

Is there a reason why I couldn't have this sort of mix-and-match system?

The 'fat' radiators need a higher flow remp than undertloor heating, typically 35-50 degrees.  Underfloor typically needs lower; 40 or less.   You can have the UF heating on a separate circuit to the rads; more complex (and maybe bit more expensive) but plenty have done it.  I have all rads and am happy with it.  

Reed_Richards

I've looked it up and apparently the UF Heating would most likely be on a separate circuit with a dedicated pump and blending valve that mixes the return water with the central heating water (at radiator temperature) to achieve a suitably lower temperature for the UF water.  As @shinytop says, even with an ASHP you tend to use radiators that operate at a higher temperature than UFH although if you have the space then the "fatter", i.e. lower operating temperature, your radiators the better the efficiency you will achieve.

The thing that I'm not clear about is whether a mixed system is any cheaper to run than one that is entirely radiators.  The heat load of the building will be the same either way and because you have some radiators then the temperature you need to heat your water to will be the same either way.  So it looks to me as if a mixed system would have the same running cost as an all-radiator system.  

Rodders53

What electric radiators have pumps in them??  Fans for convection yes... 
All outside walls:  they aren't 'through the wall' aircon/heat pumps by any chance? https://www.hvachowto.com/top-through-the-wall-heat-pump/

UFH needs good floor insulation and in my experience of oil-fired UFH down, radiator up even when installed in new builds is not good.  {Probably carp installers 14 years ago?}
Cold spots on the tiled floors.
Room too cold or too hot - especially when solar gain toasts the room(s).
Need to be clairvoyant / expert weather forecasters to heat rooms in time.
As oil boiler is noisy and under our bedroom we can't start it up early enough to get the rooms warm first thing without disturbing our sleep.
Which is why we have installed multi-split aircon/heat pumps.

Stick with radiators!  Plumbers understand radiators.  They just need to get (their head) around the low flow temperature requirement for sizing rads and pipework.

wittynamegoeshere

I'm not expecting any efficiency gain from underfloor heating in itself.  Honestly the main benefit would be not having to work out where to put a massive radiator between all the furniture.

But I'm expecting an improvement in energy efficiency as a result of pulling the floor up and getting a thick slab of foam insulation under it.

The concrete floors in the two main living rooms are those that have sagged quite severely, the centre is an inch or two lower than the perimeter.  So replacing the floor would improve insulation, damp-proofing and give a level floor.  It would seem a shame not to stick some tubing in at the same time.

The bedroom floors have sagged too, but I'm pretty sure they could be screeded up to a level fairly easily.  Plus they have less furniture, so putting a large radiator somewhere that isn't going to be blocked by furniture should be easier.