UFH off existing boiler

[ash_scotland88]

Looking at our extension plans and we're looking at keeping our boiler, just moving it.

I previously thought you can't run UFH and radiators off a single zone CH system due to flow rates and how UFH works. Some more reading appears to be telling me otherwise using diverter valves.

Can anybody care to explain it some more?

Is it still not an ideal system as UFH isn't separately controlled? Although likes of TADO thermostat valves could change that.

In existing house it's wood based floor and joists with crawl space underneath. I thought I read at one point being able to retrofit UFH using the gaps between joist and insulation but can't find it again, anything I do find is going from above then screening over.

Muchos gracias

 

[Madrab]

Basically it comes down to temperature and flow rates, UFH heating runs at a lower temperature than your rads and depending on the size of UFH area/pipe run lengths, flow rates need to be set to ensure consistent temperatures over the whole area.
Yes you can retrofit UFH into a suspended floor with joists, usually it would use spreader plates to hold the pipework and distribute the heat. These systems can be fitted from underneath.

 

[hard-work]

UFH can be off one radiator zone. Just create a sub-zone off the rad zone, using a blending valve and pump to lower the water temperature in the UFH sub-zone loop. the UFH pump circulates around the UFH circuit with the blending valve only allowing hot water to enter the loop when needed to maintain the UFH loop's temp. An electric zone valve can be fitted to cut off the UFH zone and pump when the room is up to temperature.

The UFH only comes on when the rads are on. A bit crude but cheap, working OK most of the time. The best is to have the two on separate independent zones with separate time clocks. UFH has to come on before the rads to warm up the floor as its response is slower.