Moving On Up With Underfloor Heating
Rapid growth in the underfloor heating market has led to an array of new products being introduced, enabling the installer to cut down on installing times.
Ground floors in most new builds are screeded floor constructions with UFH typically installed in the screed. However, for wooden suspended floors, there are many alternatives and each installation method has its own merits and application.
Pug mix solution:
The tried and tested method of installing UFH in suspended floors is using a pug mix. High quality insulation boards are placed between the joists and held in place with battens, so they are fully supported and the top of the board is approximately 20mm below the top of the joist. The UFH pipe is then clipped into place, typically at 200mm centres onto the insulation board. The joist must be notched to allow the pipe to pass from one ceiling void to the next. Once the pipe is laid, a dry mix of 8:1 dry sand and cement is smoothed over the pipe work and tamped level with the top of the joist so when the finished flooring is laid, the sand and cement mix is in contact with the underside of the flooring.
This system allows good heat transfer from the UFH pipework to the floor surface. The method is particularly suitable for buildings with higher heat losses and also for combination with lower temperature heat sources such as heat pumps. This, combined with tighter pipe spacings, allows for the flow temperatures to be kept as low as possible to improve the Coefficient Of Performance (COP) of the heat pump. The weight of the sand/cement mix adds approximately 28kg/m2 for joist spacing of 400mm. Although this weight is acceptable for most constructions, we recommend ratification by a structural engineer.
When notching is not an option:
Where composite joists such as eco-joists are being used and notching is not permitted, it is advisable to use an 'over-joist' construction. This is the same as the 'between joist' construction except 20mm battens are fitted to the top of the joist and insulation is fitted flush with the top of the joist. This means the batten is notched - not the joist - to allow the UFH pipe to run from one joist section into the next. The dry sand cement mix is added as above, between the battens, and the flooring fitted and fixed to the battens.
Heat diffusion plates for upper floor installation:
The heat diffusion plates (also known as spreader plates) method is a simple, lightweight system and considered an easy method of installation. However, it only gives 85% coverage as compared to the 100% the dry sand cement method delivers.
Heat diffusion plates for floating floors:
Another upper floor installation method is using aluminium heat distribution or spreader plates, in conjunction with insulation boards. These can be applied to a finished floor and will increase the depth of the floor by 30mm to 50mm, dependent upon the thickness of the insulation level. For this type of 'floating floor' the spreader plates fit into grooved insulation boards - the insulation boards are laid down and the heat diffusion plates are fitted on top. UFH pipe is then slotted into the heat diffusion plates and the floating floor fitted above this. Using a layer of builder's paper between the plates and the floating floor will reduce expansion noises.
Heat diffusion plates for 'between the joists' installation:
This method can also be used between the joists, with the plates being fitted to bridge the gap between the joists. Insulation is fitted beneath, in combination with battens to support the insulation and plates. The pipework is then pushed into the plates, with notching to allow the pipework to go from one joist area to the next. The flooring is then fitted over the top, fixed down to the joists.
Heat diffusion plates for 'fit-from-below':
If a floor has already been fitted then a 'fit-from-below' plate can be used and is fixed to the underside of the already installed floor. The pipework is pushed into place with the insulated boards fitted from below and secured tight against the 'fit-from-below' plate with battens.
The SlimFix™ installation method:
Another upper floor system is to use SlimFix™, a radiant reflective foil, which reflects the heat from the UFH pipework back up to the underside of the floor.
The reflective foil is unrolled across the joists and allowed to hang down approximately 50mm below the top of the joist. Clips are then fitted over the joist so that the pipework is suspended in mid air above the foil. This system is very light, simple to use and remarkably quick to install.
Conclusion:
Seek impartial advice and choose an installation method that best suits your project needs.
For more information log onto www.continental-ufh.com or call 0845 108 7001.
