Electric underfloor heating

[AwkwardPaws27]

I know it is horribly expensive to run, but I'm considering a mat system for a small (8x4.5ft) bathroom. Is it possible to have them on a timer or do they take too long to heat up?

It's in a downstairs extension off the kitchen. We only have space for a shower upstairs but I like a relaxing bath & it handy for bathing the dog, so keeping the downstairs bath.

The room gets cold compared to the rest of the house, current towel radiator doesn't make a big difference & I thought having an electric system, maybe on a 1 hour timer, might make it more pleasant?

yes friend has a timer so go ahead...they have wood floor so heats up fast.

A back extension may have an uninsulated roof and uninsulated walls. Fix those and make sure you have a effective extractor fan.

We had a very cold back bathroom, it is on the corner of the house and exposed.

We had insulation put on the wall behind new plasterboard, replaced the towel rail with a proper radiator and have underfloor electric heating that comes on for an hour in the morning.

It's lovely now.

replacing the towel rail with something efficient was a huge difference.

@PigletJohn

A back extension may have an uninsulated roof and uninsulated walls. Fix those and make sure you have a effective extractor fan.

@PigletJohn any suggestion what I should be asking the builder for in terms of insulation? I mentioned that when they visited to quote and they said it shouldn't be needed. They're coming back tomorrow for more detailed spec discussions so would be great to to know what to ask for!

I'd rather spend the money insulating than on an electric matt system that has ongoing running costs if that should fix the issue...

I've already bought an vent axia extractor to go in there (no extractor at all currently).

I'd just say (from bitter experience) if you do go with the electric underfloor heating, put thin tiles on top, not massive, fat travertine. I guess that the thinner the tile, the quicker the heat will make its way through to your feet. Ours took forever.

measure how thick the walls are

probably at a window

might be 4 inches, 9 inches, 13 inches (plus plaster)

is it a pitched roof or flat

if pitched, is there access to it from the adjacent roof or through a hatch

how old is the roof, and the addition

if you are having it tiled, and can afford to lose a bit of internal space, you can have the internal walls lined with insulation and a cement backer board to tile on

an effective extractor fan will keep it drier, hence it will feel, and be, warmer.

How far away is the boiler or the nearest radiator

Thanks @PigletJohn

Wall inc tiles is about 10 inches.
Flat roof, refelted about 4 years ago.
Extension date uncertain; at least 20 years, probably more like 30.

Boiler will be around 20ft away (currently about 7ft, but being moved as part of kitchen extension. Radiator currently the other side of the wall (in the kitchen) with a towel radiator in the bathroom itself.
New rads in kitchen will be around 10ft away due to layout change.

Builder has advised we'll lose around 70mm each way (35mm per wall) if add insulation... will need to remeasure as it's only 148cm wide (with current tiles in situ) and I wanted to get a toilet and bath side by side... not entirely sure I'll have the clearance (it's 760mm minimum for toilets, isn't it?) unless I find a skinnier bath...

easiest thing would be to change the towel warmer for a radiator, the biggest you can get. Wide is better than high. Towel warmers have quite how heat emission, even lower when they are lagged in a thivk insulating jacket of towels.

If you have a wide rad you can have towel rings above it, the towels will catch some of the warm air rising.

I think the bathroom is probably uninsulated, and losing a vast amount of heat. You can drill a hole in the ceiling and have a look, there might be a whisper of fibreglass up there but I doubt it. Walls may be solid.

Long ago I had an uninsulated house. On frosty nights a 3kW fan heater was unable to keep the bedroom comfortably warm. The day after insulating the loft, the heater clicked off and electricity usage dropped to maybe a quarter.

consider having the old ceiling pulled down, insulation added, then reboarded and skimmed. Now is the time to do it, before you redecorate and refit. Otherwise you will have to wait until it needs a new deck.

@PigletJohn

consider having the old ceiling pulled down, insulation added, then reboarded and skimmed. Now is the time to do it, before you redecorate and refit. Otherwise you will have to wait until it needs a new deck.

Thank you!

So it siunds like this plan should work;

• proper rad with decent BTU (will go find a calculator now but probably 1500-2000)
• insulate the ceiling (but leave the walls as I need the space!)
• don't worry about UFH

I'd try to line the walls with an insulated backerboard before tiling. You can have the old plaster knocked off to save a fraction.

the insulated boards are not very thick, but much better than brick or plaster, and will reduce condensation.

Thank you!
Probably a daft question - we were only planning on tiling to half-height - would going full height retain heat better?

Only if you added insulation.

OK thanks

I don't have the figures to hand

But consider, for example, that an uninsulated cavity wall loses almost ten times as much heat as an insulated cavity wall*

The improvements are dramatic.

Your layer will not be as thick as that, though.

*Example figures:
A range of U-values are indicated below for the purposes of comparison only:

Solid brick wall: 2 W/(m²K)
Cavity wall with no insulation: 1.5 W/(m²K).
Insulated wall: 0.18 W/(m²K).
Single glazing: 4.8 to 5.8 W/(m²K).

www.designingbuildings.co.uk/wiki/U-values#:~:text=Typical%20values,-U%2Dvalues%20are&text=Solid%20brick%20wall%3A%202%20W,to%205.8%20W%2F(m%C2%B2K).

Ceilings are probably in there somewhere too.

@PigletJohn

I don't have the figures to hand

But consider, for example, that an uninsulated cavity wall loses almost ten times as much heat as an insulated cavity wall*

The improvements are dramatic.

Your layer will not be as thick as that, though.

*Example figures:
A range of U-values are indicated below for the purposes of comparison only:

Solid brick wall: 2 W/(m²K)
Cavity wall with no insulation: 1.5 W/(m²K).
Insulated wall: 0.18 W/(m²K).
Single glazing: 4.8 to 5.8 W/(m²K).

www.designingbuildings.co.uk/wiki/U-values#:~:text=Typical%20values,-U%2Dvalues%20are&text=Solid%20brick%20wall%3A%202%20W,to%205.8%20W%2F(m%C2%B2K).

Ceilings are probably in there somewhere too.

That's really helpful.

I wonder if I can get away with just insulating the outer walls of the extension (only two of which are in the bathroom) to minimise the mm lost...

Terrible diagram attached; we are moving the current separate toilet into the bathroom, & that space will have a stacked washing machine and tumble drier.
I could ask them to insulate the outer walls (yellow) and ceiling...

you don't insulate interior walls

I wouldn't expect them to be planning that (unless they have not done correct site survey)