Wet underfloor heating

So apparently i’d be daft not to put underfloor heating into my extension (build starts in March provided the weather hasn’t delayed the builder too much). I see the benefit of underfloor heating and realise now is the time to instal as retrofitting is not feasible, but one thing that bothers me is that it takes time to warm up, so your on demand heat isn’t that good and its not doing the efficiency any good to let it cool and warm it up twice a day.

So for those with wet underfloor heating out there what’s the score? Do you leave it on 24/7? If so how does it compare to normal radiators? Do you have any additional heating to give you a quick burst of heat while it warms up?

I will also be getting a new super efficient boiler with all the bells and whistles so that shouldn’t be an issue.

Cheers.

The whole ground floor of the barn is UFH (1,500 sq ft).

fed in 6 zones, but not independently zone controlled (yet…Im enclosing the boy’s toy room in a few months so will need to fit zone valves on the manifold for more control)

I have mine setback during the day and night to 14 degrees with morning and evening boost starting at 5am till 8am and 3pm to 9pm respectively back up to 18 degrees. It provides a general background comfort level. To boost in the evening I use a woodburner, but dont fire it until at least 6ish so as not to bring the air temp up too soon above 18deg and prevent some heat getting into the slab. The energy in the slab keeps the floor from chilling and smooths out the heat in the house over the whole evening.

Remember slow to heat up can mean slow to cool down. The thermal mass of the floor can be a benefit.

Thanks chaps, that’s helpful. So am I right in thinking that on cold winter days underfloor heating won’t warm the room up so its nice and toasty and I need a secondary heat source like a fire or wood burner?

You can control the reactivity of the slab by using different types of screed. We have laid systems using 10mm pipe against the normal 16mm under 30mm of pumped liquid screed containing bonding fibres for strength. This heats up pretty quickly, the only downside is you need more circuits as each one is limited to 65m ( I believe )

You can control the reactivity of the slab by using different types of screed. We have laid systems using 10mm pipe against the normal 16mm under 30mm of pumped liquid screed containing bonding fibres for strength. This heats up pretty quickly, the only downside is you need more circuits as each one is limited to 65m ( I believe )

I can have the UFH do all the heating to a toastie 20 degrees if I want. But it’s more efficient for me to boost air temp with the stove than use the floor. I have a completely open plan barn. It takes a lot of energy to maintain 20 degree throughout whereas keeping it at 18 with the stove boosting evening temps near the sofa is more efficient

Thanks chaps. I’ll get it installed and see how I go. On the basis I’m getting a new boiler too with the latest controls I can probably set a separate programme to manage the UFH independently of the rest of the house so I can probably optimise it and run it for one year to see if we feel we need an additional heat source. It’s a simple 3.5m extension to a modern house so not a huge floor area.

If you think you might want a radiator at a later date when you plumb the extension you could provide for a radiator connection hidden out of the way and isolated. But as you say, its not a big area and if you you lay out at the right c-c pipe distances for the W/m for the floor material/covering and emission rate you should be fine.

Underfloor will be fine.
As Stoner says run at setback temp when heat not needed, temperature raised when heat is needed. Unlike a radiator based system though because of the slow response times you tend to have the heating come on earlier and also go off earlier because of the thermal mass effect of the floor slab.
You will need to make sure house is well insulated and as draught free as possible. You will also find that you are comfortable at a lower temperature. Personally I wouldn’t bother with a radiator. Once you’ve got used to controlling it you will have no problems. Also as it uses lower flow temperatures than rads it is far more efficient.

aye. forgot to mention that my UFH runs at just under 40degrees, whereas the upstairs radiators are more like 60+.

wobbliscott

Coincidentally, I just got an email in my inbox from http://www.underfloorheating1.co.uk/ who I use for DIY materials saying that they will be at “The Home Building and Renovating Show, which takes place at National Exhibition Centre, Birminham, West Midlands, B40 1NT, from the 27th to 30th March 2014”

and that:
We will be happy to look at any plans you bring with you on the day, so we can assess your requirements. We also provide a Free CAD drawing with every system sold and we are happy to say we will beat any like for like quote.

They’ve offered free tickets too – email them to get them.