Timber flooring is a popular floor finish in both contemporary home design and in period home renovation and is an ideal material to use with an underfloor heating solution.
In this guide we’ll explain:
- Is underfloor heating suitable with timber floors?
- The differences between timber and engineered wood
- The qualities of timber
- How best to install floor heaters with timber flooring
- The best water and electric floor heating systems to use with timber flooring
Can I use Underfloor Heating with Timber Floors?
Both hydronic and electric underfloor heating systems work well with timber floors, as timber conducts and holds the warmth produced by the floor heater and radiates this into the room. The natural properties of timber also mean that it has a fast heat-up time whilst also resisting heat from escaping too quickly, making timber helpful in maximising the energy-efficiency of an underfloor heating system.
Differences between Timber and Engineered Wood Flooring
Whilst both timber flooring and engineered wood flooring can be used with an underfloor heating system, the differences in their density and moisture content values can lead to different heating requirements.
When we refer to timber, we generally mean natural hardwood – that is wood that has been cut and treated specifically for flooring and most commonly produced as floorboards. When considering installing floor heating with a timber floor finish, the quality of the timber is very important. Quarter-sawn timber is the best choice as it has been cut in such a way that when it absorbs moisture, it is unlikely to bow or warp.
Engineered wood is a man-made product that often utilises a hardwood timber finish on top of a plywood inner core. All engineered wood is designed to limit the growth and shrinkage caused by moisture in the atmosphere but due to the softer wood core, cheaper engineered wooden flooring can swell over time, in some cases causing a failure of the floor heating system. It’s always best to talk with your flooring supplier about the suitability of using your chosen floor finish with underfloor heating.
The Qualities of Timber when used with Underfloor Heating
As a natural material, timber is affected by its surrounding environment and there are some key things to think about when installing an underfloor heating system with timber floors.
The thickness and density of timber flooring can impact on the performance of the system and we recommend that timber thickness should be no more than 18mm. Also, as wider timber boards will often show more movement than more narrow boards, we recommend that the ratio of thickness to width should be in the region of 7 to 11. A board with a thickness of 16mm and width of 160mm would give a ratio of 10, so is ideal.
It is typically recommended that a maximum floor surface temperature of 27°C should not be exceeded for timber flooring but this not strictly accurate. This temperate instruction is based on historic research exploring growth and shrinkage rates of timber floors and it was at 27°C that the expansion of timber tested was deemed ‘invisible’ to the naked eye. This temperature is now an industry-wide recommendation, but timber floors can be heated to a higher level if necessary, however if your flooring supplier recommends a maximum surface temperature of 27°C then you should follow this advice.
You can secure the temperature restriction of the timber floor using a Warmup Thermostat that accurately controls the underfloor heating system to provide you with an optimally heated room. As part of your project you should also always get a heat loss calculation done in order to ensure that underfloor heating meets the room heating requirement.
Expansion and Contraction
All wood is hygroscopic, meaning it absorbs moisture from around it and this moisture causes both timber and engineered wood to naturally expand and contract over time. This moisture content can vary depending on what kind of timber you choose and the environment of where your floor-heating project is located. With the changing seasons a timber floor will grow and shrink minutely as the indoor humidity changes. If installed incorrectly, this swelling and contraction of a timber floor can impact on the responsiveness of a floor heater.
Retrofitting Underfloor Heating with Suspended Timber Floors
Suspended timber floors are a common structural element in many period properties and we offer a range of floor heating systems specifically designed for suspended timber floors.
Retrofitting a floor heater with the original timber floorboards, as opposed to a new timber floor finish, can make for a complicated project. You can retrofit a system in one of two ways: from above or from below.
Installing a water system with floorboards from above requires removing all timber flooring before laying back down after installing the heating system; this is typical for a ground floor installation. Retrofitting from below is recommended for an underfloor heating installation on a first floor or upper level timber floor and means ripping out the ceiling in the room below and installing the heating system this way, in a back-to-front method.
Wet underfloor heating is often recommended for use with suspended timber floors and the Tectora Joisted Batten System is a perfect solution. This system utilises the void between the floor joists as a space for the water underfloor heating pipework and insulation panels. You should also be aware of making the underfloor heating system as airtight as possible to keep the warm air in and the cooler external air, out.
You can also use electric underfloor heating with suspended timber floors but in these cases, you would use the original timber floorboards as a subfloor and install the electric system on top of it before laying down a new flooring finish.
If you are installing a new timber floor with an underfloor heating system, there are a couple of key things to think about to guarantee a successful first-time installation.
Acclimating the Timber
Due to timber’s moisture content and the effect this has on growth and movement, we recommend letting the timber flooring acclimate to the environment inside the room it will be fitted to. Part of this process is an installation heating cycle during which the floor surface temperature should be kept at 15°C and the air temperature between 15-22°C. The atmospheric relative humidity should be between 40-60%.
After installation, the floor should acclimate for at least 48 hours before turning the system back on. The floor temperature should be limited to 15°C and increased by 1°C a day until the desired floor temperature is achieved. It is advisable to check the temperature restrictions with your floor manufacturer as the ambient temperature will depend on the season. Always check with the flooring manufacturer the suitability of the flooring for use with the heating system.
With regards to the hygroscopic properties of timber, it’s also worth being aware that if you are using screed as part of an underfloor heating installation with a timber floor, that screed will add excess moisture to the timber, so we recommend allowing screed to dry at a rate of 1mm per day. A 10mm expansion gap around the room is also recommended to prevent any future problems with the expansion and contraction of a timber floor.
Best Underfloor Heating Systems for Timber Floors
The Tectora Joisted Batten System is an ideal water underfloor heating solution for suspended timber floorboards. Its aluminium diffusion plates spread the heat evenly throughout the timber floor finish and its pipework and insulation is fitted within the void between joists.
Our Total-16 system is another great hydronic choice and is perfect for renovation projects as its low-profile build up will not sustainably add to the floor height.
Our Foil Heater electric underfloor heating system is recommended for floating timber floor finishes and its unique design offers rapid installation times.
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