I've read lots of useful information on this group about hot water UFH, but has anyone any thoughts about how to control it? This is for a GF extension that is going to be the kitchen. Concrete floor with the usual insulation underneath. Combi boiler driving the existing central heating.
I'm wondering how to enable the UFH to be kept on (perhaps timed, or perhaps just thermostat) independently of the main heating thermostat/controller.
Thanks
On 21 Mar 2006 07:45:29 -0800 someone who may be "Nigel Frost" wrote this:-
It needs to be on a separate zone, ideally with a lower flow temperature. Both are easily arranged, look on the web for how to do it with the aid of controls and valves.
An ideal solution is a thermal store, which can provide water for radiators and underfloor heating at separate temperatures and domestic hot water at useful flow rates. However, these are not as cheap as some alternatives.
Convert to S-plan system if you're not already. ie. seperate motorised valves for CH and HW. Add a third motorised valve for the UFH system. Replace the existing controller for one with three zones or add a new controller for the UFH and add it in so it switches the boiler on too. The Honeywell CM67 is popular and works well. Reply again if you need more info on how to modify the wiring - it's not too difficult though.
The UFH control would run the pump for the UFH system. I have wired in an over-temp cut-off too that ensures the pump will cut out if the water temp goes above 50degC. (Otherwise the screed turns to dust apparently!)
As regards the UFH water temperature, as someone else said I guess the best way is to use a lower-temperature boiler or thermal store. I've used a thermostatic mixing valve which works very well so far. Just set and forget!
Jon.
First of all, get a three way time switch. I did. It works. Only bugger was having to add a relay so that firing up the main boir for e.g HW didn't cayuse the secondary UFH pump to come on.
Secondly, think long and hard about independent zones and thermostat placements. I didn't :-) I have to do a fair bit of manual adjustments..fortunately the main UFH area is all one big space where we tend to leave doors open, so temperature equalises over the area fairly well.
The message from "Nigel Frost" contains these words:
You may well find you don't need to. The thermal mass of 3" of concrete will keep it warm for quite a considerable time after the heating's gone off.
The system I've installed (but not yet connected) in the conservatory has a thermostat in the return path. That in effect sets the temperature of the floor.
But sadly keep it cool a long time after it has come on. I reckon a 1-3hr lag.
On Tue, 21 Mar 2006 19:48:03 GMT someone who may be Guy King wrote this:-
That is a good reason for having it on a separate zone. It can then be turned off before the radiators (and turned on before them, for example in the morning).
Thanks for all your help - very useful indeed. It seems that a separate zone, with it's own controller, is the way to go. I'm a bit wary of the systems with only a thermostat on the return path, as the water entering the UFH pipe will be hot! Other systems I've seen advertised on the web have a CW blending valve, room thermostat, and a pump. I'm curious as to why the UFH needs its own pump, when the boiler has a perfectly good one.
Nigel Frost
Thats because of the temp reduction thing. You want to be still pumping hot water around even when the boiler has cut off...and the blending valve may have more or less isolated you from the CH main circuit.
Also the CH pump will not work efficiently when the blending valve has almost shut off the flow and is in 'recirculate' mode.
The ideal for UFH is moderately warm water flowing fairly fast through so that there is little temp differential between flow and return, otherwise you get uneven floor heating and possible cracking.
Whereas normal CH is piping hot flow, and cold return.
I can't see the point of a a thermo on the return path either. Its the forward path that needs to be prevented from getting to hot,and a packaged pump/manifold/blending valve/motorised valve like wot polyplumb do is a really good way to go.
It made installation for mine a complete snap. And the little flow meters on the manifold are a boon when setting up and balancing.
The message from The Natural Philosopher contains these words:
It effectively sets the temperature of the slab. Regulating the inlet will not control the temperature of the room as well.
Only things I have seen is as ours, the thermostat head/valve is on the return, but operated by a remote sensor strapped to the inlet manifold thereby allowing cool return to recirculate without further heat pumped in.
It does not set the temperature of the slab.It sets the temperature of the return water. Under conditions of slow flow and hot water the slab takes on many different temperatures. The function of the thermo mixing is to make sure none of these are excessive.
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