Water Underfloor heating

DadisSkint

Hi

We are having a large ground floor extension at the rear to open up kitchen to create on large family /kitchen room. This extension includes a new boiler heating system replacing my combi to a conventional system boiler. Originally the new extension includes a radiators around the family / kitchen room.

A house down the road is having similar extension by same builder, but instead having water underground heating - no rads.

My question is - is water underground heating worth it and does it 'heat' the room. My builder said it would cost an extra 2k to fit. I like the idea of not having to worry where the rads go etc...

Any advice is appreciated.

matelodave

Three years ago we replaced all our storage heaters with a new wet underfloor heating system called Polypipe Overlay which sits on top of the existing flooring and it's heated using a heat-pump so the flow temperature is significantly lower than a conventional boiler.

We've so far had three very cold and prolonged winters with it and are very impressed as it's kept us nice and warm, no cold spots and, as you point out, no radiators anywhere. It also seems to produce less dust and in comination with the heat pump it's very economical to run.

We can keep the thermostat down a couple of degrees below what we'd normally have it as there aren't any cold drafts and it's lovely standing in the kitchen or bathroom with bare feet.

It's much slower reacting than normal radiators as it runs at a lower temperature 35-50 degrees rather than 70-80, so don't expect it to heat up the room within an hour or so like radiators. Do make sure that it's correctly specified for the rooms it's being used in. It works best with ceramic tiles on top of it but we are using it with tiles in the kitchen, bathroom and utility rooms, laminate in the hall and carpet in the bedrooms, lounge and dining rooms and they all seem to work OK. If you do have carpet over it then make sure that you use low-tog carpet & underlay to maximise it's performance.

It would now be my first choice if we were doing it again although I'd make sure the floor insulation was uprated as well to make it even more efficient

marcus_h

matelodave - that is what I am looking at, and I note that the Polypipe Overlay can be had in 18mm thickness. Did you use that slim version? Also, what flooring depth did you have underneath?

matelodave

Hi Marcus - we've got the Polypipe Overlay 18mm hard panels (a cementitious stuff) rather than the foil faced polystyrene - our installer said he didn't like the polystyrene stuff.

Our actual flooring below the overlay stuff is 18mm T&G chipboard floor on joists with a ventilated space to the ground about 18" below except in the kitchen, bathroom and utility where it is 18mm ply (replaced because the chipboard stuff had fallen to bits. In hindsight it might have been beneficial for us to have stuffed some insulation between the joists before we put the floor back down - it would have probably improved the efficiency of the heating system.

We've got two manifolds as there is a big floor area (140m2) to cover and it made it easier to lay the pipework. The piping is connected as 16 loops and controlled as 7 zones with a thermostat for each zone (which in hindsight is probably a bit excessive). A heat pump feeds the water at about 35-40 degrees which is the ideal temp for a heatpump.

If you want more info I can communicate via E-Mail with more details

marcus_h

Thanks for the info. Just one question at the moment (I'll send you my email if I think of more!). We have solid floors (cement) in the house that we are moving to - that should in theory be better in terms of insulation, shouldn't it? It's encouraging to hear that you like your system - depending on grants, RHI etc, I am leaning towards GSHP with UFH.

matelodave

I'd be inclined to lay something like 10mm Kingspan under it if I were going to put the hard stuff directly onto an uninsulated concrete floor to help insulate it and reduce any downward heat loss. I suspect that the polystyrene stuff would have a bit of insulation itself. You can lay laminate, wood and carpet on top of the polystyrene boards - they have to be overlaid with 6mm ply. If you are tiling then you need to use the cement based boards and you can tile directly onto them.

The void under my whole floor is ventilated to the outside so I assume that it can get quite cold under there when its cold, wet & windy outside. So mine would probably benefit from some insulation just to improve it's efficiency as all it's got is 18mm of chipboard between it and the void. We don't notice it, but I'm sure the heatpump probably has to work a bit harder to compensate.

If you look at some of the heat loss calculators you can get some idea of how much heat gets lost through different types of floor, bearing in mind that although heat rises you'll probably lose some through conduction into the floor slab. However, that said, if it's a relatively recent build/refurb you might find that it's already got a load of insulation under it, in which case it might be better to lay it directly onto the concrete so the whole mass heats up

It's probably worth having a chat with PolyPipe to see what they say.

I've got some photos of our installation if you are interested