underfloor heating on economy 7

[jedisparks]

Hello all,

Went to look at a job this week at a 1960s property. When the house was originally built electric heating elements were installed within the screed and have been operating happily on economy 7 ever since and client is happy with it. Just wondering if anyone knows of this still being done like this these days?

Reason I'm asking is although I have installed many ufh systems myself, these have always been heating mats installed on insulation boards with tiles on top. The job I'm looking at for the client is a 34sqr/m extension which he would like electric underfloor heating in and wants to know if it will also be energised through economy 7.

There is no oil or gas boiler at the property, so solution has to be electric.

It's a big floor area and will be expensive to run either way but on economy 7 it will not be very controllable. Have spoken to several heating system suppliers who all say to avoid in screed systems as you're paying to just heat up the floor slab. Despite that the in screed systems are readily available and I'm wondering under what circumstances they are recommended and used?

Any thoughts on how to proceed?
Thank you

 

[charlie76]

The in screed systems do heat up the slab but the heat then radiates out into the room. Its like saying radiators only heat the metal of the radiator but no heat is given off in the room. The heating suppliers you have spoken to are talking rubbish. I work in construction and in screed systems are pretty much all you see these days in new schools, hospitals etc. Granted they are wet systems and yes you are right the electric ones would cost a fortune to heat. It would be pretty straight forward to calculate the running cost and then perhaps approach your client and pre-advise them, after that I would say its up to them.

My understanding with these systems (or at least the wet ones anyway) is that they run all the time at around 12 to 15 degrees C, you don't allow the slab to cool so although running on E7 would be cheaper when it is running, continually turning off would allow the slab to cool and then require re-heating the following evening so I imagine it may not be the best way to do it.

All the above assumes the slab/screed has the correct insulation underneath it, I guess around 100mm minimum of foam but you will need to check the building regs for the requirement there. If it has crap insulation then yes you will be heating up the slab and the ground below which again is going to add considerably to your running costs.

I guess at the end of the day if the customer is happy to pay the heating bill then so be it.

 

[7029 dave]

In the 70's electric heating elements were in the ceiling too, we had them in our house, 15 amp circuits per room on a room stat per room.

 

[topquark]

Can still be done like that. Often in flats with no mains gas for example. Usually economy 10 these days ... but watch the suppliers meter as sometimes there are only four tails and not five; so you then need a timer to control when the heavier current users chime in (often via a contactor arrangement).

 

[jedisparks]

Thank you for your replies. It's a while until the job kicks off so will look into it a bit further over the coming weeks. I'm probably going to suggest the same system that I typically install. insulation backer boards, then heating mats, then a few mill of levelling compound, then tiles. 24hr/7day programmer. Nice and quick to heat up as and when he needs it, can also set a sensible temp set point for when they're not there so as it doesn't cool down too much. Once up to temp, which won't take long, it will just kick in occasionally with the stat.

I'm not convinced that it will more efficient with element cables in the floor slab on economy 7 because most of the heat is going to be released during the day when the client is at work.

Thanks again