Electric Underfloor Heating, does it work?

NovaGSi

Good morning all,

new to the "Boards"

I am building an extension, 35m2, onto my bungalow.

I am considering electric underfloor heating as the primary source and the floor covering will be carpet.

The floor will be concrete with 80mm insulation.

I have contacted a number of suppliers and they all suggest/advise installing heating cables in the concrete slab. The suppliers state that this solution is the most efficient and cost effective way to heat the room.

Does electric underfloor heating really work as a primary heat source?

Opinions/testimonials appreciated.

Cheers,
Mick

NovaGSi

Anyone??

Cheers,
Mick

Hoagy

Electric underfloor works out to approx 100 watts per sq mtr, maybe a bit more.
So your 35 sq mtr extension is going to have a requirement of about 4KW

It works best when the temperature is maintained at a comfortable level, the inertia in the system means it won't heat up quickly.
To maintain the comfortable temperature the heat is going to be on for at least 50 percent of the time.
If you get ESB dual tariff metering and utilise the night rate, you might have 8 hours at 8cent per unit plus say 4hours at 16cent per unit, which works out to app 5.12 per day, almost 36 euro per week.
Plus you will be paying an extra cent per unit for all your other electricity.

Electric underfloor is really only suitable for bathrooms and the like.

And it's not recommended to lay carpet over it.

dewsbury

Hoagy wrote: »

Electric underfloor is really only suitable for bathrooms and the like.

And it's not recommended to lay carpet over it.

I agree with the above.
Definately not for carpets!
Best with tiles (or special wooden floors).

We have gas powered underfloor heating (with hose like water pipes under then floor). I would imagine that this is dearer to install but cheaper to run.

dewsbury

Hoagy wrote: »

Electric underfloor works out to approx 100 watts per sq mtr, maybe a bit more.
So your 35 sq mtr extension is going to have a requirement of about 4KW

It works best when the temperature is maintained at a comfortable level, the inertia in the system means it won't heat up quickly.
To maintain the comfortable temperature the heat is going to be on for at least 50 percent of the time.
If you get ESB dual tariff metering and utilise the night rate, you might have 8 hours at 8cent per unit plus say 4hours at 16cent per unit, which works out to app 5.12 per day, almost 36 euro per week.
Plus you will be paying an extra cent per unit for all your other electricity.

Electric underfloor is really only suitable for bathrooms and the like.

And it's not recommended to lay carpet over it.

Hoagy, you seem to know a lot about underfloor heating.
I am a domestic user of 8 years with gas powered underfloor heating.

I have recently concluded that 24 hour heating at a low temperature works best. We control the low temperature by adjust the boiler rather than using our thermostats which are in 4 points around the house.

The fact that the system is on 24 hours seems to have made a big difference. And the usage of gas is not that high at all because of the low temperature.

It has taken 8 years of either a cold house or a huge gas bill to come to the above conclusions!!

Hoagy

dewsbury wrote: »

I have recently concluded that 24 hour heating at a low temperature works best. We control the low temperature by adjust the boiler rather than using our thermostats which are in 4 points around the house.

The fact that the system is on 24 hours seems to have made a big difference. And the usage of gas is not that high at all because of the low temperature.

That's very interesting, it's confirmation that underfloor is ideal for use with a heat pump, because the water temp is lower.

Unfortunately you can't control the temp of the electric heat in a similar fashion, it's either on or off.

ircoha

dewsbury wrote: »

Hoagy, you seem to know a lot about underfloor heating.
I am a domestic user of 8 years with gas powered underfloor heating.

I have recently concluded that 24 hour heating at a low temperature works best. We control the low temperature by adjust the boiler rather than using our thermostats which are in 4 points around the house.

The fact that the system is on 24 hours seems to have made a big difference. And the usage of gas is not that high at all because of the low temperature.

It has taken 8 years of either a cold house or a huge gas bill to come to the above conclusions!!

Just wondering if the HW is on a separate system as it is recommended to have the HW at 60c to kill off any 'bugs'. Long term low HW temp might not be the best idea

dewsbury

ircoha wrote: »

Just wondering if the HW is on a separate system as it is recommended to have the HW at 60c to kill off any 'bugs'. Long term low HW temp might not be the best idea

The HW is on a separate (electrical) system but this is primarily because it existed when we got the house in the first place. We can get hot water from either system which is useful if you have a boiler problem.

Having said that I have not sufficient knowledge to say whether the HW from the underfloor heating would be sufficiently hot for a shower etc. (given that we now keep the temp low on the underfloor heating.)

We find that having a separate system useful as it means we turn the gas off entirely for perhaps 5 months per year.

I am no expert here .... just a user.

c class 226

Only just read OP
We put on a 40 sq. m extension about 4 years ago. Ended up with electric underfloor heating with a tiled floor. Oil fired heating radiators in rest of house.
Hard to give a break down of running cost of electric underfloor. One problem with it is its lack of flexibility - because it runs on nightrate electricity the room is lovely and warm first thing in the morning. Which is no use to us as we are out all day. I would have preferred to run a hot water system which could be fired up during the day to give heat in the room in the evening.

fishdog

Electric underfloor works out to approx 100 watts per sq mtr, maybe a bit more.
So your 35 sq mtr extension is going to have a requirement of about 4KW

It is not as much as 100 watts per sq meter. It is more like 26 watts (aprox. from memory). I know this for a fact as I have connected many Devi and Flexel mats. I have always fed them from a spur outlet which is fused at a maximum of 13A.

Dont take my word for it, you can get free leaflets about it from Chadwicks, Eurosales, Kellihers etc.

If you get ESB dual tariff metering and utilise the night rate, you might have 8 hours at 8cent per unit plus say 4hours at 16cent per unit, which works out to app 5.12 per day, almost 36 euro per week.

Remember when you switch it on it is not on all of the time. The stat has it switching on and off all of the time (unless you turn the stat right up, but it will be very hot then).

Unfortunately you can't control the temp of the electric heat in a similar fashion, it's either on or off.

This is not correct. There are good controlers from Devi and even better ones now from Hotfoot, ring them on 01 2871172. They give great control in a trendy backlit display with a stat and 7 day clock.

c class 226

The Devi mat is a different beast to proper underfloor heating and runs on quite low power- cant remember the rating but would run from a 13A supply and is used to heat bathroom tiles etc.
True underfloor heating would be nearer 100w /sq. metre. Our 40 sq. m extension is pulling somewhere around 5kw on a Devi controller.

fishdog

The Devi mat is a different beast to proper underfloor heating and runs on quite low power- cant remember the rating but would run from a 13A supply and is used to heat bathroom tiles etc.

I my experience Devi mats will heat any floor surface that is tiled really well with great control and cheap enough to run too. I used it in my kitchen that was about 40 sq. meters aprox in my last house. It was fed from a 13A spur outlet on a local socket circuit. I would descibe it as "proper underfloor heating" because it is the only form of heating in the kitchen and we were never cold. Set point was 21 degrees C.

I found it ok under carpet, but not as good.

They are very popular now. Every house seems tp have or want it in the bathroom. I installed it under the shower tray in a wet room, worked very well.

True underfloor heating would be nearer 100w /sq. metre. Our 40 sq. m extension is pulling somewhere around 5kw on a Devi controller.

I have never seen this type. Who makes it and where do you get it?? Why does it require so much power? I assume you are using a contactor and a 4 or 6 sq. cable?? I assume it can reach the set point very quickly, the Devi mat cant.

c class 226

What I think of as a Devi mat is about 3 mm thick, is laid on top of a concrete screed and just under tiles. We have them in both bathrooms.
What we have in our sittingroom that pulls the power is the heating wires buried in about 150 mm of concrete screed. It is also a Devi system but heats the whole floor whereas the tiles on the mat go cold once the system switches off.

Hoagy

fishdog wrote: »

It is not as much as 100 watts per sq meter. It is more like 26 watts (aprox. from memory). I know this for a fact as I have connected many Devi and Flexel mats. I have always fed them from a spur outlet which is fused at a maximum of 13A.

From the DEVI website

"Depending on which type of floor you are building, you have the choice between devimat™ in 100 or 150 W/m2."

fishdog

From the DEVI website

"Depending on which type of floor you are building, you have the choice between devimat™ in 100 or 150 W/m2."

Interesting, thanks! I never saw that before!

Oilrig

We have a Flexel 170W mat in the family bathroom (quite small) it would not heat the room without the rad on. It is a very good tile warmer but can't get the temp up on its own. (upstairs - ie wooden floor)

The instructions recommended a 3A MCB/spur fuse.

Devi

Devi sell three floor heating systems.

Devimat - The most commonly known electric heating floor system.
4mm element sitting on a self adhesive mesh. This system would need a very thin screed like tile adhesive or leveling compound. Has an output of 100w/m2 and 150w/m2.

Deviflex - Not as well known but has been used in alot of apartments and one off houses. 7-8mm element sitting directly on 50mm Kingspan TF70 or equivalent then 35mm - 100mm screed poured over it. Output ranges from 100 - 234w/m2. Capitol cost of Deviflex is about 50% cheaper than Devimat.

Devicell Dry - Popular in Scandinavia but not that popular in Ireland. Its basically an insulated diffuser plate for the Deviflex. Completely dry system, no screed needed. Only for floating wooden floors. Only 100w/m2. About the same price as Devimats.