Advice on underfloor heating

[realslyshady]

Hi folks! Looking for a little advice, if anyone has the time to give it.

We renovated and have been living in an 1850s terraced railway worker's house for years, so we've seen a little of the issues involved with older properties. We've just sold it and moved to a 5-bed, 3-storey semi-detached 1880 townhouse in need of total renovation. It's in a real state. The air bricks are clogged with tarmac, the gable has been cement pebbledashed, the rear elevation needs the cement picking out and repointing in lime. The offset kitchen has a cement slab floor and the rainwater goods are completely gubbed. Two external stone lintels and one internal wooden lintel are wrecked and need replacing. The property has been occupied by one person for about 40 years, and only one room ever heated in all that time. It has also suffered with significant subsidence over the years (the attached property has been underpinned) though that seems to have stopped. Nearly all the plaster has blown. Fair to say it has the odd issue with damp, and needs a huge amount of work.

We're not trying to restore it completely, more of a renovation. We've made an open plan ground floor, and we're having central heating installed. Some of the ground floor joists are shot, about a third of them need to be replaced or reset, and half the floorboards need to be replaced. Our builder feels that laying a new floor would be easier, cheaper and more secure, and that's led us to consider investing in underfloor heating. While I see a lot to commend the idea, I'm also wary of doing anything that's going to cause problems along the line. With that in mind, I was wondering if anyone here has had underfloor heating installed in place of suspended timber floors, and if so — any advice? Any regrets? Any warnings? We're working on a budget, trying to balance what the property needs to get dry with making a longterm family home.

Would appreciate any advice or suggestions. Thank you!

 

[fernicarry]

Was discussed not too long ago, try a search. Partly depends on what sort of finished floor surface you are looking for. The heat won't get through regular floor boards so forget that. Modern engineered (laminate) floor coverings *might* be suitable (if that's your thing). Ceramics or stone should work.

We put UFH between the joists in our kitchen. There was no original floor to keep, just chipboard and horrible tiles. We wanted to avoid building the floor up too high which is why its between the joists.

It was a bit of a homebrew, thermafleece hung between the joists on netting, polypipe overlay boards cut to size and sat on battens, plywood and (real soon now) tiles on top. It works well for Spring/Autumn but in winter needs another heat source, we have an oil Aga to fall back on. To be fair the whole house struggles when its as cold out as it is at the moment.

I'm happy enough with what I've done, its a big uptick in comfort level for us, but the bar was set pretty low to begin with. If I was doing it again I'd know what details to worry about to make a better job of it. I'd be a lot more careful with the insulation as I think air movement under the floor (which you must have!) is tending to suck the heat away. Not enough crawl space underneath to remediate unfortunately.

Doing it for a whole open plan ground floor is a bit of a different proposition. Will you have a secondary heat source such as a wood burner in case the UFH doesn't keep up? If you're doing a big renovation then you should really look at how you can improve the overall performance of the building at the same time. We put insulation in the kitchen wall studwork which I think has helped us somewhat but we could have done a lot more.

 

[MikeG]

As I said last time, UFH only works with solid floors. If you are contemplating replacing your timber suspended floor with a solid (concrete or limecrete) floor then UFH is a possibility*. However, it works very differently from radiators, and so is less successful when there is a hybrid of UFH and radiators on the same floor. Basically UFH is gentle and slow-response........but radiators are rapid response. The heating can be on for an hour or more with UFH with absolutely no change in the temperature in the room, and my last house didn't reach its maximum temperature until some 6 hours after the UF heating came on. This complicates the controls if you are mixing up UFH & rads.

Don't even think about having UFH upstairs.

* Changing to a solid floor in an old property has potentially enormous implications for the damp control in the property. This is something that needs thinking through very carefully. It is readily do-able, but it shouldn't be done without a holistic plan which includes consideration of materials on the external walls, DPC, and so on.

 

[Flyfisher]

. . . However, it works very differently from radiators, and so is less successful when there is a hybrid of UFH and radiators on the same floor. Basically UFH is gentle and slow-response........but radiators are rapid response. The heating can be on for an hour or more with UFH with absolutely no change in the temperature in the room, and my last house didn't reach its maximum temperature until some 6 hours after the UF heating came on. This complicates the controls if you are mixing up UFH & rads.

Absolutely. Ours takes about 4 hours to get up to heat, though it also takes a long time to cool. I think it's great for background heat and keeping the chill out of the building fabric but I'd say it also needs something else for that finer control. We use a wood stove, which seems to work well, though I guess rads would work as well. Good underfloor insulation is also essential otherwise a lot of energy will be wasted heating up the ground beneath the floor.

 

[fernicarry]

UFH only works with solid floors

I think you mean "is more effective".

 

[MikeG]

UFH only works with solid floors

I think you mean "is more effective".

Thanks, but I'll choose my own words.

If I said "UFH is more effective in solid floors than suspended timber floors", would that stop you putting it in? I am quite happy to stick with "it only works in solid floors", because those are the only floors in which it can warm a house to acceptable modern standards. Saying what I said in the way I said it gets my meaning across clearly.

 

[88v8]

Radiators would look better with a fleecy knitted jacket in a colour-co-ordinated design, but wouldn't work terribly well.

Trying to project heat through an insulation layer is perverse.
Wood is an insulator.

Ivor

 

[tobydog]

Don't even think about having UFH upstairs.

We have UFH in the new and contemporary kitchen extension to our 16th C thatched cottage. It works great because we have a serious amount of insulation. In the old part of the house (joined by a link) we have CH by radiators with the exception of the upstairs bathroom where we have a towel rail acting as the radiator plus UFH. It's an electrical system made by Warm-Up and I couldn't recommend it enough. The floor was plywood (about 12mm) so the plumber (refitting the bathroom two years ago) laid a similar thickness again in order to carry the weight of floor tiles and prevent cracking. The extra thick plywood also acts as a good insulator. It's all controlled by a clever box on the wall outside the bathroom and doesn't use much electricity if you manage it properly. It's very toasty when it's on but I have to admit that it can be a little chilly on the toes if the CH and the UFH are off at the same time.

I certainly wouldn't recommend it for the whole upstairs but a big thumbs up for a bathroom - even upstairs.

 

[MikeG]

...... the upstairs bathroom where we have a towel rail acting as the radiator plus UFH. It's an electrical system......

Those electrical systems (normally under-tile) are fine for warming the floor in a bathroom, but they are not suitable for space heating. (You know that of course, I'm just putting it on record, again).

 

[tobydog]

Mike - the system has default settings and the one we go for set's the floor temperature to 24C between 6pm and 10pm. Like most bathrooms (I presume) the towel rail doesn't have a thermo valve so it's at the mercy of the downstairs thermostat. That's set at 19C and the radiator heating won't always trigger on a milder day. In this case we rely solely on the UFH and I have to say, in all honesty, it heats the bathroom space which is pretty average size. I have to confess that this is only the case because of the 24C default evening setting. When it goes down to anything near or below 20C then I agree you only get warm feet.

 

[Flyfisher]

In terms of heating design and calculations, isn't UFH effectively the same as a standard radiator? Both are heated surfaces that transfer heat into an enclosed space. As far As I understand things, UFH only runs at a lower temperature than standard radiators because they have a much larger surface area. Indeed, if they ran at the same temperature as a standard radiator then the room would become far too hot. Conversely, standard radiators require very hot water because their surface area is relatively small in comparison with the floor area.

On this basis, an entire bathroom floor at a temperature of 24C will surely have a significant warming effect on the entire space above it?

 

[realslyshady]

Thanks for all the advice and pointers, peeps. I think we've decided against UFH. If the benefits had been huge, then we'd have found a way to afford it, but I'm not sure we'll get enough out of it to justify the additional expense. Looks like replacing a couple of joists and several scores of floorboards will be the plan — as well as freeing up those airbricks, breaking up the yard outside, insulating between the joists, etc., etc., etc..

Thanks for your time and advice — much appreciated.

 

[tobydog]

I do agree that the obvious downside of upstairs UFH is that there is no heat store. Once it goes off it goes cold fairly quickly. On the plus side it does heat up fairly quickly and we can override the timer at any time.

 

[88v8]

.... the towel rail doesn't have a thermo valve so it's at the mercy of the downstairs thermostat. That's set at 19C and the radiator heating won't always trigger on a milder day.

A good way to heat the bathroom, as I've mentioned before, is to have a rad &/or towel rail in an always-on loop so it comes on with the hot water &/or the CH. The towel rail/rad then has its own thermo valve.

Ivor