Effects of heating systems on timber floors:

Introduction

 As the colder months approach us in autumn of each year, that familiar inkling to turn the heater on at night creeps back in. Before you know it, winter is in full swing and the heater is running for half the day and most of the night. The degree of heating needed, and the different systems used will vary dramatically depending on your location, but it’s safe to say that the further south and/or the higher you live, the more internal heating you will probably be using. This information sheet outlines some of the possible effects that various internal heating systems can have on timber floors and what steps can be taken to help minimise these unwanted effects. 

The climate experienced with heating systems in the home 

Timber floors including solid timber, engineered, laminate and bamboo flooring are all affected by the dry conditions created when the heater in your home gets turned on for long periods of time and it’s helpful to understand what is happening and how you can help minimise the impacts of internal heating on your timber floor in these colder times.

Temperature and relative humidity are the two key factors that influence the internal climate or environment within a dwelling. An increase in the temperature inside the dwelling will cause a lowering of the relative humidity and with this the drying capacity of the air increases. Low relative humidity will result in timber and similar flooring releasing some of its moisture to the air, and thereby reduce in moisture content and shrink. As such the moisture content of a floor is affected by changes in the heated environment. The term equilibrium moisture content (EMC) is often used. EMC can be thought of as the moisture content that timber will slowly head towards and settle at under set conditions of relative humidity and temperature. Therefore, if the conditions inside a dwelling are maintained at 20°C and 50% Relative Humidity (RH) then the flooring, depending on its current moisture content will either take up or lose moisture to naturally settle at a moisture content of about 9% as shown in the table below.

Cold, wet winters can mean the opposite for timber floors in homes 

It would be natural to think that in a place like Melbourne, Victoria a timber floor might shrink in the dry weather during summer and then expand in the cold, wet winter. This would be true if the home was always exposed to the external temperature and humidity, however when we factor in the effect of internal heating during winter, the EMC drops dramatically in the opposite direction, even beyond that which would be experienced in the dry summer, as shown in the adjacent graph. When the EMC elevates during winter due to the higher RH and cooler temperatures as shown in the blue line, the internal EMC shown in red plummets as heating is introduced from May until September. (Note that the graphs are based on external relative humidity values and a less extreme variation would be expected inside a dwelling).

Common heater types, their impacts on timber floors and how to reduce them 

Ducted Heating – Gentle, well distributed heat when ducted from the roof, but when ducts are in the floor, the timber surrounding the ducts is highly prone to cracking. Keep ducts clear of anything that could push the heat back down onto the floor including couches, rugs or cabinets. Even ducts that sit under a kitchen bench lip can cause excessive drying of the floor below, as the air gets deflected back down before it fills the rest of the room. Run in the low 20’s to avoid over drying the air. Turn down to 16- 18 degrees Celsius when not at home, so that the floor and home does not become too cold, yet a reasonable temperature is maintained that is not too far from the normal running temperature. If timber shrinkage or cracking around the ducts is a concern, choosing plastic duct covers instead of metal ones may help reduce the heat transferred to the timber floor as metal covers get much hotter.

Portable Heaters – Quick, isolated radiant heat. If left in the one spot or low to the ground, can quickly dry out the timber in front of it resulting in gapping, cupping and cracking in the surface of the boards. Nonflued gas heaters can produce water vapour, which is not necessarily a bad thing in a dry, warm space but ventilation is required to remove moisture and gas emissions. Using portable heaters in small rooms can quickly dry out the floor resulting in cupping and shrinkage. Raise heaters off the ground, position them where there is air flow to direct the hot air away from the front of the heater, place a reflective material like tiles underneath and in front of them, move the unit from time to time to avoid over drying a particular area. Turn portable heaters off when leaving the room for any substantial period of time. Start on a lower heat and slowly turn it up higher as required so as to not shock the timber floor, which can weaken boards and hasten the onset of cracking.

Open Fires and Solid Wood Fuel Heaters – Ambient and cosy, yet these fires can really suck any remaining moisture out of the room, as they tend to burn at high temperatures for prolonged periods of time and have little control over the temperature output. General shrinkage can occur in the localised room where the fire resides and excessive gapping, shrinkage and cracking can result directly in front of the fire place from exposure to the intense heat. Similar effects have been seen with in-wall gas fire units that have been either set too low or do not have a hearth underneath that deflects the heat. Ensuring that the fireplace is raised off the ground and is surrounded by a deep-set hearth will help push the heat out instead of down into the floor in front of the fire. Some may say that a mat or rug in front of the fireplace will reduce the gapping in a timber floor but long-term exposure to such intense heat will most likely result in some gapping, so a hearth will be much more effective than a rug over time. Limiting the amount of fuel added to the fire at any one time will reduce the intensity of the heat produced.

Split System / Reverse Air – Similar to ducted heating from the roof, as the units are usually set high on the wall or in window spaces and produce a gentler heat than other types of heating. Having said this, they usually only have one point of origin for the heat, which means they often need to run longer and/ or at higher temperatures to warm other areas of the house. This can leave the area in front of the heater susceptible to very minor drying and shrinkage if over used. Maintaining a temperature in the low 20’s and turning this off overnight will help reduce impacts from this type of heating.

 Hydronic Heating – This form of heating is most commonly found underneath the floor or on the walls as panels. In slab heating and under floor hydronic heating have very specific operating instructions when a timber floor or similar is installed above it, and this is probably best explained in the ATFA information sheet #36 – Floors with underfloor heating. In regards to the effects of this type of heating on a timber floor, when installed in the subfloor, this heater is essentially slowly drying out the timber from underneath so extra care needs to be given to make sure that the operating temperature remains as low as is comfortably possible and when turning it on after not using it for extended periods of time to slowly bring the temperature up, so as to not shock the timber floor. Excessive heat from under the floor can result in cupping, crowning, shrinkage, gapping and creaking. If installing a new solid timber floor over hydronic heating, a narrower board would be considered a safer option, as wider boards are more susceptible to cupping and movement.

Other general tips to help maintain a stable environment in the home 

Some simple ways to help add some moisture in the air around the home when the heating is being run continuously include… • Placing some vases of water with flowers throughout the house • Buckets of collected water in the bath tub or shower when not in use • Indoor plants • Washed clothes drying on racks • Opening the dishwasher as soon as the cycle has finished to release the steam • Or using a humidifier All these things will help to slow down the process of dry air pulling moisture from the timber floor, which can help minimise potential gapping and movement in your floor.

‍