Underfloor Heating Advice Please

martint999

I am getting to many opinions on my underfloor heating requirements.

My existing house was built in the 1970s and has a concrete slab which I assume is not insulated. I am planning a large rear extension and want to add UFH throughout. I am not planning on digging out the current slab as its too much money so I need to think about what UFH system is best.

I assume I have two options:

1 - An overlay system consisting of insulated panels of about 25mm depth which the pipes it in, so in reality the pipes once in the grooves are probably only about 10mm above the current slab. I then board this over and lay my choice of floor. This is what I have been told:

Overlay System
Positives - Easier to install, high heat output, low build up
Negatives - Much more expensive

Traditional System
Put down e.g. 40mm of insulation, lay pipe directly on top or on preformed panels and screed
Positives - deeper insulation, cheaper, with a poured screed can get a totally flat floor and the screeds will retain the heat
Negatives - Lose about 100MM of headroom.

So thats what i understand, although someone said to me today that with the screed system the floor will lose heat more quickly, but I could not understand that if there was more insulation. Is it because there is a slightly greater distance between the pipe and the floor covering? But doesn't the screed retain heat.

I am getting so lost in opinions I am not sure which way to turn. Help would be so appreciated.

phil24_7

I would reconsider digging down.

By doing this you can ensure correct levels of insulation beneath the slab and a proper dpm can be laid.

Doing it this way will also mean that the floor will hold a lot more heat for a lot longer and you will not loose 100mm of head height. This might not seem like a lot but it will when it comes to your internal doors!

Regards

martint999

Thanks for relplying I just dont thinks a cost option

phil24_7

What about if you can do the digging out yourself or perhaps get a labourer or a young relative to come and do it?

A skip for the rubble and a weekend pocket money for a teenager will save you a fair whack.

phil24_7

If your having a large rear extension, the builder may do this without a massive mark up. It could be a few hundred or maybe an extra 1000 or so, you wont know until you ask and it will be a small percentage of you overall build.

What you spend doing this will help you save some money with your underfloor heating as well as ongoing heating costs and general comfort in the house.

FreeBear

phil24_7 wrote: »

What you spend doing this will help you save some money with your underfloor heating as well as ongoing heating costs and general comfort in the house.

A close neighbour built an extension last year - He was vacillating over UFH and debating whether to dig out the 1960s slab. In the end, dug the whole lot out to a depth of over 12" and installed insulation & UFH. He is pleased with the heating and reckons it was well worth the extra cost & effort.

Yes, digging out even a small area is a lot of effort, noise, and dust, but you will regret it a few years down the line. If the builder has a mini digger on site currently, and access is good, the extra cost may not be very high.

bouncydog1

Neighbour put in an electric system without digging out and you really notice the step up into the room. We got the builders to remove the floor screed in our refurb and level with self levelling screed, then put down 12mm insulation. On top of that went a micro system pipe layout in insulating board, topped by a ply floor. Amtico layed on the top. Room (which is c34 sq m and half glass) is pleasantly warm.

Not sure what the running costs will be, but you wouldn't know it was a retro system as floor height is the same as the rest of the house.

Although I would love large pipe underfloor heating throughout the house the cost for us was prohibitive, so this is next best solution and we keep rads in the rest of the property.

System

Neither of the two options are that satisfactory imo, they are both very compromised, if you don't have the budget to dig and insulate properly then I would just leave the ufh to the new build portion where it can be done well, installing over an uninsulated slab will ruin the efficiency of the system and likely have a huge additional running cost, so cheaper to instal but you'll lose that over a few years anyway...