Underfloor Heating Design for New Build

21 Oct 2013
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United Kingdom
Hi all, thanks in advance for any responses.

We are about to build a new build two storey timber framed house. We had always thought we would be using wet underfloor heating on the ground floor with Radiators upstairs and wet underfloor heating in the bathrooms (3) upstairs as well, with towel radiators.

We have been advised that this is inefficient because the water for the underfloor heating needs to be about 40 degrees but for the radiators about 70 degrees and that we should have underfloor throughout, and basically you heat the water to the maximum and then add cold to cool it for the underfloor. We have some concerns as is if we zoned the ensuites with the bedrooms as has been recommended then in my opinion there is minimal use as the main reason for the bathroom underfloor heating would be to take chill off the tiles. I think we therefore have a number of approaches and am keen to hear opinions.

1. Full wet underfloor heating, somehow we would zone the bathrooms separately, towel rails in bathrooms would be electric with a time delay switch to power them.

2. Full wet underfloor heating downstairs with radiators upstairs and towel rails. Wet underfloor heating in the bathrooms upstairs and just cope with the fact it's slightly inefficient.

3. As two, but use two different boilers, one for radiators and hot water and one for underfloor heating. (obviously there are ongoing maintenance costs here as well as additional install costs)

4. Wet downstairs and in the bedrooms upstairs, use electric underfloor heating in the bathrooms to control it separately, along with electric towel radiators.

5. Any other options there may be that I haven't thought of.

The bathrooms are not massive so the floor space needing to be heated isn't huge, I just want to be able to have the bathrooms on separate from the bedrooms as ceramic / porcelain tiles still get cold, even in the summer.

Hope this makes sense. The first of many questions I would think.
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Forget idea 3.

UFH in bedrooms only works if the free floor area gives enough heat output for the room. Often there is too much furniture and so the w/m is insufficient. A lot of this depends however on the quality of the build and the amount of insulation.

Electric UFH in bathrooms is usually fine as are electric towel rails.

Rads do not need to run at 70 degrees either. Mine seldom need to go above 50, and I have rads up and UFH downstairs. the UFH is blended down dynamically by an electronic mixer receiving instructions from my thermostat which also changes the boiler running temperature depending on heat load through the zones.

It might not be worth sub zoning the ground floor if insulation levels are good. Mine is one large open plan zone.

Also worth considering having the towel rails plumbed back to the boiler so they are on a separate circuit that comes on all years round from the boiler. Cheaper to run and maintain than electric.
Thanks Dan,

I think I have read what you are saying as follows.

Wet UFH downstairs and in the bathrooms upstairs. Radiators in the bedrooms, and plumb the towel rails back to the boiler on a second circuit so they can be on all year round if wanted.

An alternative option for bathrooms upstairs would be to use electric underfloor heating.

We will zone downstairs but they will probably be only 4 zones it's a big house. One of my thoughts upstairs is to have the bathrooms that are used every day which are also next to each on one zone and the 3rd guest onsuite on a separate zone.
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Wet UFH in bathrooms is usually more ball ache than its worth - electric is fine if there is another heat source. The only issue is that I have yet to see an electric UFH controller that is remotely usable, although I understand Heatmiser do one.

Not the best controls out there, but certainly not the worst.

How you zone the place depends on the heat source. We've nearly finished one where there is an air source heat pump doing the heating with a gas boiler doing the hot water cylinder and towel rails. I have wired a changeover switch in so if the ASHP goes tits up the customer can push a button and the boiler takes over the UFH too.

There are many ways to skin a cat - and part of the problem is that builder's plumbers are usually clueless with design - as are the builders, architects etc. I'm always cautious of anyone who is "designing" a system who spends most of their working life behind a desk.

I spend a sizeable amount of my working life sorting out their cock ups.

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