Underfloor heating isn’t just a few pipes in the ground, there have or should have been careful planning and design gone into the system to allow it to work correctly, more so with low temperature systems and heat pumps.

With underfloor heating there are a few things to consider when getting this installed

  1. Heat Loss
  2. Flow temperature
  3. Insulation in floor for downward losses
  4. Floor build up, depth, type of system
  5. The amount of pipe in the floor and the centres
  6. The pattern of which it is laid
  7. Floor coverings and their effects
  8. Manifold locations

Underfloor heating is around 55% radiant and 45 % convection and because the majority is radiant it creates a much more comfortable environment at much lower temperatures  compared to radiators .

What should be first considered is the heatloss of the property and the rooms in the property as this will give you a guide of how much pipe is needed and what flow temperature is needed to overcome these conditions at design conditions.this is usually done through a calculation that works out your room areas and wall,floor and window types to give a more accurate answer to how much energy your building fabric loses

With this information we can now look at any awkward rooms or index rooms that need excess heat and try and achieve the lowest possible flow temperature to achieve your designed indoor temperature. This can be then installed throughout the whole house and installed in a way to maximise efficiency and work alongside your heatpump to maximize the heat pump’s output and efficiency also.

Any ufh that is on a ground floor would ideally need to be insulated underneath to stop any downward losses through the building fabric and to stop any wasted energy and uk building regulations require downward losses do not exceed 10 watt per mtr.Alongside this a perimeter edging strip this allows the screed or concrete to expand and contract during any heat up and cooling down periods but also stops any thermal bridging from the screed to the external walls.

There are also many different systems on the market for all different occasions,many of these are not suitable for heat pumps ideally with a heatpump system you are looking for a much greater flow rate 4 times faster than a gas boiler so pipe sizing is necessary here to be able to overcome the pressure loss at these high flow rates. smaller piped systems might have a much larger pressure loss are would require buffers or separation and require larger pumps to overcome this, all affecting efficiency and increasing energy usage.

There is also a very careful consideration when picking these ufh systems on what there output is per m2 and if putting it in will be enough to overcome your heatloss. Lets take for instance a 16mm mlcp system in screed with 150 centres running at 45 deg the output per m2 is 141.3 watts we have to be careful here what flooring we choose also (but i will come onto that later).Now the same mlcp pipe in a reflective aluminium foil lined in floor voids at 150mm centres running at 45 deg is only 45 watt per m2 so a loss of half just from different systems this is limited as the centres are limited to 150mm and are like this on many systems

But with the right  systems, This is where we can now look at the system and see if we can maximise the space and the output by putting more pipe and closer distances apart to increase the output but by doing this we may be able to lower the flow temperature even more thus increasing efficiency of the heatpump and output.

Along with this we do need to be careful of floor temperatures as some flooring will not tolerate higher temperatures as mentioned above 45 deg in screed 150 centre will achieve a floor temp of 32.3 deg not suitable for any glued system or engineered flooring

Floor coverings also have a massive impact on ufh and are something that i see overlooked time and time again. if your installer has designed your system and assumed you are having tiles everywhere then he assumes your output on a 16mm mlcp system in screed at 45 deg is 141 watts m2 but now you decide to put hardwood flooring the output of that floor is now decreased to 84.1 watts even worse you decide you want 1.5 tog carpet or maybe an engineered 22mm flooring, the same ufh will now only achieve 70 watts half the output you originally had with tiles, so it is very important to get this correct and work with your installer

A few quick example of this for a heat pump:

  • You have a room 5mtrs x 5 mtrs your heatloss for this room is 2.1 kws
  • We decide to run the heatpump at 35 deg to maximize your efficiency (scop rating around 4.5- 450% efficient)
  • Flooring is confirmed tiles and we put all pipework in at 150 centres
  • Output per m2 84.3watt per m2 total 25m2 is 2.1kws perfect
  • All underfloor is laid and now hardwood flooring is being installed
  • Output now per m2 is 50.1watts per m2 total 25m2 is 1.25kw (we aren’t hitting heatloss)
  • So now the flow temperature needs raising to 50 deg having a huge impact on you efficiency (scop rating around 3.5 -350% efficient)
  • Output now 85 watts per m2 total 25m2 is 2.12kw

So that’s a loss of 100 percent efficiency just by laying a different flooring.

So please make sure your underfloor heating installer knows what he is doing and asks these questions before any installation and understands them.

Why it's important to get underfloor heating installed correctly!