How to zone underfloor heating

If you want to go two way couple the hot water to e.g the UFH system timer wise.

Fit three master stats anyway and run as three zones. As well as zone/radiator stats.

The tank stat can be the sole HW stat

I'd have them on the same output as the CH, but have a separate stat for each area. Gets more complicated with the piping, but fairly straightforward and common. You can then set the floor for, say, 15 degrees, and the CH for 20.

NO. never on the same timer. Screed floors take HOURS to warm fully, and you may want more intelligence on the thermostat to minimise overshoot.

The number of zones in a building depends on the occupation pattern. Some areas will be constantly occupied, others perhaps infrequently so. So these areas can be divided apart and independently controlled. Also if some areas are significantly warmer than others.

So fuel savings can be made.

This has been done in large commercial buildings for years. It only becomes viable in domestic houses as fuel prices rise. After all you can turn radiators off manually. However even now, you'd need a big house to make it worth while.

The alternative method is for each zone to have it's own heat source/ boiler which in some cases works out cheaper.

With regard to underfloor heating. This allows boilers to run efficiently because of low water temperatures.

However, it can't be turned on and off daily as it has high thermal inertia. Probably going to take a couple of days to warm up from cold. It needs to be installed in a well insulated building. Sometimes the UF heating is used as "background heat" and topped up from other sources as required.

Our situation is the same: UFH downstairs and radiators upstairs (plus hot water). The radiators and hot water are controlled by a conventional timeswitch, but not the UFH: as far as the boiler is concerned that's 'permanently on'.

The UFH zones (we have 6) each have their own UFH thermostats; they switch between 17C and 21C according to the time of day, but again they never turn the system 'off'. The UFH can, and does, come on in the middle of the night in order to maintain the 17C minimum.

Richard.

Only if the boiler isn't required to feed anything else! As our boiler feeds radiators and a hot water cylinder in addition to the UFH it runs at a fairly high flow temperature of 65C. The UFH manifold arrangement incorporates a thermostatic mixer valve to reduce the temperature to 45C for that circuit.

Richard.

Unless you actually want to turn the UFH off via a programmer then there is no need to have a 3 zone controller. The programmable stats in your 3 UFH zones should do their job and these should have a permanent live.

That is a reasonably valid point EXCEPT that most UFH zone valves controlled by stats are NOT master stats as such and do NOT stop the pump running. Not the UFH pump: not the boiler pump.

They are analagous to TRVs in radiators.

Now you COULD fit motorised valves, at which point the points you make become valid, because you can wire OR the outputs and use them to control the pumps. But that is not the way most installations work.

In the end you need a time because you don't want to heat when you don't need to. That might be in the thermostats or it might not, but its still needed.

What all this means is that UFH needs to be thought through carefully and 'conventional thinking' does not apply.

Take care with what UFH system you have ... many have a temp that is much less than rads and if you run them at rad temp they will fail.

That is why many are used with Thermal store with 2 heat exchangers ....