Underfloor Heating Advice Needed

[MdB]

Has anybody got any experiance with fitting underfloor heating?

My current floor is concrete with a DPM and with a high local water table moisture is being forced up the walls. For this reason I would like to replace the floor with something breathable.

My heating system is also on the way out and I'm thinking strongly about fitting a heat pump to heat the house. Heat pumps work best with under floor heating so I'm thinking of solving both problems in one go.

The only option I've heard of so far is to use LECA mixed with lime as a base to insulate the floor together with lime screed to fix the under floor heating into on top.

I am sure there must be other options available (hopefully a little cheaper). Any good suggestions on solutions or websites to look at?

Cheers, MdB

 

[KN]

Ours was expensive I remember for the screed cost about £4,000 took them about 4 hrs and 2 mixer lorry fulls to get it to 65mm thick.
It has some kind of waste mixture from power stations in it I think, and it conducts the heat well from the water pipes.
I must admit it seems to work really well with the ground source heat pump and the house walls seem quite dry at ground level. We have a radon barrier and then insulation to meet current building regs so all in all it add up to being quite thick a thickness.

Karen

 

[Gervase]

UFH can be fitted onto a concrete floor but will make for a thick floor, as the general spec is for 50mm of insulation (celotex or similar) beneath the pipes and 65mm of screed covering.
With a 150mm limecrete slab with a 100mm foamed glass or LECA substrate you can do away with the celotex, and if you're careful with your levels and neat with the piping, you can get away with just 50mm of screed.

£4000 for a domestic floor screed is outrageous! I've just done one in lime for a client and wished I could charge that much :shock:

 

[Tom]

We removed a thick concrete floor for the same reason as you...water being pushed up the walls. We installed a LECA/Limecrete floor with wet UFH and no DPM, so the whole thing is breathable. It works a treat and I'm thoroughly pleased with the outcome!! I'd be happy to answer any questions you have

Jaqy

 

[MdB]

Thanks all for your replies.

Karen, do have anything bad to say about heat pumps and UFH? I've yet to come across any downsides (when installed with enough insulation) though I am sure they must exist. I don't have any experience of either UFH or heat pumps and don't know of anybody who has so need some confidence building to go for it.

Do you run the pump from Economy 10 electricity?

Gervase, 50mm of Celotex in the floor comes out around 0.3W/m^2.K, where as LECA / lime comes in at 0.45W/m^2.K for 230mm. Considerably worse for a lot thicker layer and roughly twice the price. I've not been able to find U values for other materials. Any suggestions on who would be good to contact to get some advise on what materials to use for the insulation?

Jaqy, what drives your UFH? Do you have a heat pump too? If so, any down sides?

 

[Tom]

Our gas Rayburn runs all our heating (UFH downstairs and radiators upstairs) as well as doing our cooking and hot water

Jaqy

 

[Fizzer]

Jaqy, PM sent!

 

[Tom]

And you have a reply Sorry, I just noticed where you are so you can ignore that question from me!!

Jaqy

 

[KN]

I've just written loads of info MdB but I've just lost it all!

PM me with any questions, I'd say in brief say all good, especially electric bills so far.
We are on economy 7 now as we have an electric aga but initially a new standard meter which had a high and low level so I don't think economy 7 really benifits as the electricity used will be after useage during the day.


Karen

 

[MdB]

I know your pain Karen. I've typed loads in the past only to lose it. I guess we need to remember to keep hitting the preview button.... (goes off and does this now).

I'm glad your results are good, gives me more confidence to proceed. My biggest question at the moment is what underfloor insulation to use. The pipe people all use Celotex type stuff but I'd rather have something breathable as long as it is good at actually insulating. I guess this is two conflicting requirements...

 

[KN]

We just went for standard as we had to have the radion barrier.
What are you doing upstairs?

Karen

 

[MdB]

What are you doing upstairs?

Now if I was Penners, you would get a rather interesting answer to that...

Upstairs is a problem. The current plan is not to fit any heating at all for the time being. We have no insulation between downstairs and upstairs and lots of air gaps and think that we will be able to survive without heating upstairs for at least one winter. We can use electric heaters in necessary if it gets too cold. In the longer term, we might fit underfloor pipes on top of the current floor boards if that looks like the best thing to do. It will lose us some ceiling height (about 40mm I believe) but I think we can live with that. The main issue is that we can't add any thermal mass to the upstairs floor as our floor beams are weak and won't take the extra weight. Heating upstairs is a bit of an issue for heat pumps as there is no good solution unless you have concrete floors.

Economy 10 electric looks ideal for heat pumps as it allows it to run three times a day, 1pm to 4pm, 8pm to 10pm and 12am to 5am. Worth looking into if you don't use this tariff already.

 

[KN]

Our pump runs all the time, there is a back ground hum! But I suppose the extra boost for heating is only after a bath/shower is run so can you delay the heating up until those specified time?

I might learn something from you!

Upstairs we have old cast iron radiators , two per room as you need bigger surface area as the water temp is lower. Well you know that.

Our heat pump was working from October last year.

Have you got a big empty space to put it in? The pipe work and units are huge.

 

[MdB]

Our pump runs all the time, there is a back ground hum!

That doesn't sound right. If is runs all the time, you don't have any temperature control (unless your pump has a variable speed control which is not how I believed they worked). Heat pumps don't like being switched on and off like a normal boiler would. Switching on / off three times a day is recommended as it fits in with the Economy 10 cycles.

Upstairs we have old cast iron radiators , two per room as you need bigger surface area as the water temp is lower. Well you know that.

That would be an option for us too though I would like to avoid it if possible as it makes the heat pump less efficient if the output temperature has to rise.

Have you got a big empty space to put it in? The pipe work and units are huge.

We are going to put the pump into the garage so that shouldn't be a problem. However, the pump we are thinkin of using (6kW) is 900x550x570mm which is the same as a normal boiler. The pipework will add to that of course.

 

[KN]

It's the pump pushing the fluid round the garden that makes the hum. The boost to the water temp seems to be once a week to high temp and on demand when it's been used. We have two heats pumps one for ground floor and a few bathrooms and one for upstairs rads and other bathrooms. They are called E11 and E9 from Ice energy.