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Underfloor heating works by spreading heat from where the pipes are (ie the concrete slab of your house) to the environment around it. If there is no insulation under the slab, or there are gaps around it, the heat will leak in every direction, not just up into the rooms you want to heat.
To avoid this, make sure the only way for the heat to go is up to the room/s you want heated.
The heat pump used to heat the water for the system needs to “breathe”. It needs access to fresh air to run efficiently. It shouldn’t be enclosed (e.g. in the garage, roof or basement), nor should it be covered or put behind a screen if it’s outside. It needs at least 2m clearance from the exhaust fan. All of these impact how efficiently it can collect the heat energy from the air around it.
It is tempting to cover it up, or put it somewhere out of view, because they are large units that make some noise, but finding somewhere discreet outside, will help it to run much better than if it is hidden away.
In systems like electric heaters and air conditioners, when we want to heat a room, we tell the unit what temperature we want, the unit works to reach that temperature (as measured by the thermostat), then shuts off until the temperature drops below the target temperature again.
This is fine for standard air conditioning, where it’s easy to switch on/off. When the heat is radiant, as in hydronic systems such as underfloor heating, and the room heats up gradually from the floor, other factors such as the amount of windows and glass, position of the sun, materials the house is made from, shade will impact how quickly the room and the house gain, lose and retain heat.
Good installers use complex mathematical equations to work out how much heat to send and when to send it to ensure the room is heated to the desired temperature.
If the thermostat is near the floor, or in a cupboard or in direct sunlight or not in the room being heated (no point measuring the heat in the hallway when you want the bedroom cosy and warm).
There is no point spending a lot of money to install underfloor heating if you then use a floor covering that isn’t suitable or doesn’t get the best heat efficiency from the system. Carpets and rugs have low heat transfer levels leading to wasted energy and extra cost. Some solid wooden floors can shrink and expand with the heat from underneath causing gaps and then buckling.
Stoneware and terracotta tiles work well with underfloor heating as they are good heat conductors. Linoleum or vinyl is another good choice but make sure it is approved for underfloor heating. If choosing wood, make sure that it has a low shrinkage rate (oak, merbau, teak) and isn’t too thick. Polished concrete is a highly efficient choice as the thermal mass of concrete means it can maintain warmth at low temperatures.
Thermal energy moves from hot to cold. When the hydronic underfloor system produces heat, it will go looking for cold air to warm up. Wherever it can find it.
The common places the heat will escape is through windows, the roof, thermal bridges (which is where the building directly connects outside with inside (walls, floors, windows, roof).
Hydronic heating heats up “things” (furniture, floor, walls etc) as well as the air. If the thing it heats, in this case the floor, is warmer than the outside air, heat will be lost to try and warm up the cold air.
The way to avoid this is to use double-glazed glass in windows, put in thermal breaks (your installer will understand this), insulate walls and roofs and under the slab, and an insulated screed system.
Like all building work, having a solid foundation is key. Before installing the underfloor heating system, the floor must be prepared properly.
If the support substrate is not level the thermal insulation boards will not adhere properly which can lead to cracking in the screed board. If moisture installation is not installed the concrete screed can bend and the installation can be cured. Installing on wet ground can release unpleasant smells, fungi and mould.
Make sure that moisture installation has been installed, the substrate is level and smooth and the ground is not wet.
There are a lot of advantages to a hydronic system such as underfloor heating- 30% energy efficiency is a widely quoted statistic – but this is only if the system has been properly designed and installed.
But there are also many ways it can go wrong – concrete mass is too large, heat leaks, poor insulation, poor pipe spacing, thermostat controller incorrectly positioned, poor design of heating loops, kinked pipes.
Having a hydronic system that works efficiently requires more than laying a few pipes and plugging in the thermostat and turning on the heat pump. Design and planning are essential to make sure all of the common mistakes are avoided and your system works efficiently and cost effectively for years to come. We can do this for you!
