How To Install Under Floor Heating – Ufh

If you have read the last few posts on this blog you will have seen that we have just installed hot water under floor heating in our new orangery kitchen extension. Several people have asked for e to post a little bit about how we went about this. No I am not the expert on the plumbing side, but I can give you an over view of what we did.

You may or may not know the situation we are in, we have extended the back of the house and combined two rooms into one. In doing so we have demolished two previous extensions and made the whole thing into one. In terms of the under floor heating this meant that there were four sections to the floor, the original to the house, two parts from past extensions and one I fitted to the part we extended. This means that there were differing qualities of work. Really I should have scrapped the two floors from the previous extensions, but time and financial constraints meant that I had to make do.

The joists therefore did not match up in terms of their widths or where they run. This makes the planning of the underfloor heating rather difficult.

However, I am jumping ahead a little here, I started off by lifting all the old floor boards, some original and some chipboard.  We then cleared out all the debris from under the floor, debris that had been left from the build, by electricians and plumbers cutting things out. The purpose for this was two fold, if you have ever crawled under a floor you will know kneeling or laying on a broken brick is not something you want to do too regularly! and in addition the clearer your underfloor the better your air flow will be, especially if like us you are going to insulate under your floor it is critical to maintain a good airflow.

As I have just said we were insulating under the floor. The ideal way to do this is by cutting solid insulation such as 100mm kingspan to fit between the joists, this is a very costly exercise and would have cost us in the region of £650 just on insulation alone.

I therefore came up with my own variation on a solution that has been used by others, that was to use rockwool style insulation held up by chicken wire. Fortunately B&Q were (and still are I believe) running an offer on rockwool insulation where you can get it for £3 per roll. Using this offer the insulation cost me just £25 (les actually as I bought too much!)

The idea is that you tack chicken wire in a trough form between the joists, making use that you use enough fencing clouts to hold the chicken wire securely. Also making sure that there is no chance that the bottom of the trough will be anywhere near the ground under the floor thus maintaining an air gap.

We then laid the rockwool into this trough, and then covered the top of that insulation with foil backed bubble insulation. The purpose of this was not so much to insulate, although it does have some insulation properties its self, it was more to utilize the foil to reflect heat from the underfloor heating pipes back up into the room rather than having it carry on down into the insulation.

We taped the foil insulation together with aluminum foil tape, which if truth be told was a right pain as the tape we used was the stuff you have to peel the back off. Once adhered to the foil it is great but it can be frustrating getting the backing peeled off. We also used this tape to tape the insulation to the joists making, ensuing that we left a 20mm gap between the insulation and the top of the joists.

We chose the John Guest 30Sq Meter Hot water insulation pack from Screwfix. Mainly because John Guest is a well known make who we trusted, our research showed that people who fitted it were happy and the pack contained everything we needed to complete the job.

John Guest Underfloor Heating 30 Sq Meters Pack

When the kit came, we found that the clips that come with the pack are designed for solid insulation, you twist them into the kingspan. This would be a very quick and simple way of securing the underfloor heating pipes, however, in our scenario with the insulation we used, these were no good, so I bought some normal pipe clips an we secured these to the joists.

The main problem when laying the underfloor heating pipes is the planning. Deciding what pattern the pipes should take, on a single room system there are two loops, these should be as close to the same size as possible. You also want to try and get the first run of the pipe, i.e. the hottest pipes across doors or windows, or in the areas where you will mostly be walking.

Once you have planned the layout, you will need to cut notches out of the joists to allow you to loop across each joist, we designed the system in such a way that we kept the notches to a minimum, basically one at each end of the room.

Laying the pipe is a very frustrating task, the pipe has been coiled since manufacture and all it wants to do is go back to its loop, so it really is a two man job if you can, once holding the reel and un-doing its coil action and the other laying and clipping the pipe in the desired pattern.

Once you have the pipes laid, they have to go into the manifold, you should consult a plumber to connect this into your central heating system. They will also need to add a room stat, this allows you to run the underfloor heating independently of the central heading in the rest of the house.

We then laid chipboard flooring over the top of the insulation and pipes, we made sure that we measured and marked the underfloor heating pipes so that we did not screw through them!

We have a 35Sq meter room, with one wall totally glass and the main part of the ceiling glass, the underfloor heating system copes very well with heating the area up. We have easily had it up to 25°C and I am sure that it will go higher, but I melt at those sort of temperatures so we keep it down to 20°C

All in all we are very pleased with the result, hopefully the insulation under the floor and the insulation in the walls and roof space will compensate for the glass wall and large orangery window we have in the roof.

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