Open-plan: mix UFH and radiators

22 Apr 2008
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United Kingdom
Have just moved into a 30's detached, and starting from ground up with CH as old boiler and cylinder are broken beyond repair.

The foot print of the building is square. With 4 rooms to make the square with staircase in the middle. i.e. double fronted.

We are doing some minor building works to knock through and create an open plan L-shape with only the front right room remaining as a sealed room. i.e. go in the left front room and you can walk all the way around to the kitchen in the back right.

Regarding the open plan area: the front left room has original wooden parquet; the 2 rooms across the back of the house will be tiled.

We'd like UFH across the back of the house under the tiles but to keep costs down we plan to keep radiators in the front room.

Thinking about heat transfer between the spaces in the open plan L-shape, the heating lag on the UFH, does this make sense or should we go all UFH or all radiators?

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As per the other thread.

Evohome, Intergas boiler. With OpenTherm

Let evo control everything then the mix won't be an issue.

Just make sure the rads are sized generously.
The time lag is always a problem and the UFH should be separately timed to offset the time lag.

But part rads will also enable the room to heat up quicker so it will not be all bad.

In fact having TRVs set a little low on the rads will enable them to quickheat the room and then the UFH will take over as the TRVs start closing as the room warms up.

You don't really describe the floor in detail but UFH all over the downstairs would be better overall if your lifestyle is pretty stable like a bank worker or teacher so the UFH time lag can be timed to suit.

He describes it enough.

Tony, the whole idea of controlling it through Evohome is that it can carry out the predictions needed to bring different zones on when required.
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For small homes it's always easy to over engineer on controls, and most UFH suppliers make the most money from controls, with the pipe being the loss leader.

Save your money on a loads of fancy controls & put it into building fabric insulation, far better bang for your buck.
Tony, the whole idea of controlling it through Evohome is that it can carry out the predictions needed to bring different zones on when required.

Yes, I appreciate that is the idea.

But I don't remember any set up facilities on the unit to tell it that its a big room with one end UFH and the other rads or where the one ( or two ) room sensing units may be.

In fact for most of the year I would expect it would work pretty well. But in the critical coldest weather I would expect that I would still get better results by setting some manual requirements on the system.
You would set them up as two zones and let them sorry themselves out. Although there is another way depending on how the ufh I is installed.
Evohome is ideal for this type of scenario, we fit it to all mixed UFH and rad jobs as a first choice.

Even did one the other day controlling 2 commercial boilers in separate churches and two sets of 60A overhead radiant electric panels.

It is also massively easier to understand than the average UFH controller; - typically these have legends of suns, moons, planets and hands, all in B&W.
use a viessman vitodens 200 with sub mounting kit. The boiler will control everything, no need for time clocks, zone valves, or cylinder stats. You get 2 CT circuits for DHW and UFH and 1 VT circuit for heating rads. why would you use anything else??
Because Viessmann controls are impenetrable to a homeowner who hasn't taken the Viessmann degree course. Their boilers haven't been particularly reliable in the UK market (I've been fitting them for 12 years, domestic and commercial).

Hands up amongst homeowners who knows what a VT circuit is? And a CT circuit?

If you know the answers to these questions, or want a boiler pump that never turns off, get a Viessmann with WC (weather compensation).
CT and VT are standard term's not viessmann ones. The controls are easy to use if its been explained and full weather comp is the best thing to happen to the industry for a long time, the old boys just need to get there heads round it.

To be honest theres no defending the first boiler they sold on the uk market as it was pants but since then the 100 series just blows the competitors out the water.
Sorry Simond is right, viessmann Controls are ridiculously over complicated, expensive, poor to use and understand, with no benefit or real term saving attached.
Much like they're boilers which are just as expensive and crap.

They are however realising they have no place in the UK by ensuring their latest offering in the complicated controls market is due for release here...

Who'd want a boiler made by a company that worked on the gas chambers(allegedly)????

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