There’s a lot of mixed information out there in regard to electric underfloor heating running costs and for obvious reasons. There are so many variables at play during installation that, in truth, no one system will run exactly the same as another. Every single home is different so there are no easy answers or figures set in stone. All projects will be working to their own set of specific conditions. Though it’s impossible to give exact figures that will be true for any system, this article can provide some insight into potential long-term running costs and how they stack up against other heating methods.
What can influence how running costs are calculated?
With any heating system, there are a number of factors that determine how much they will cost to run and how effective they will be. Here are some of the main elements that can determine the efficiency of an electric underfloor heating system:
Installing the right insulation can make your electric underfloor heating system up to 50% more efficient and makes a huge difference to overall running costs. Insulation prevents any heat generated from being lost through the substrate below and instead pushes it upwards into the room above. No electric underfloor heating system should be installed without adequate insulation because without out it, you’re looking at much longer heat-up times and higher energy usage.
The type of floor covering you decide to use with your system will have a large impact on its efficiency and heat-up times. Tile and stone make the best floor coverings due to their excellent conductivity – they warm quickly but are also slow to cool, and can reach higher temperatures than other materials. Vinyl makes a good option as it heats quickly, but also cools rapidly. Wood and carpet, however, have much slower heat up times which means that you will use more energy getting the room up to a comfortable temperature. Carpet in particular acts as an insulator and will make any system much less efficient, so you can expect to pay a lot more in running costs if this is your intended floor covering.
As with any heating system, the greater the area, the more energy you’ll need to use to keep it at the right temperature. Underfloor heating systems are no exception to this rule, so if it takes 84.3p to heat using a 10m² kit for four hours, it will be over double the amount to heat a 25m² room at 210.8p.
Room Insulation & W/m² Used
It’s not just floor insulation you need to consider when fitting an underfloor heating system. Inadequate room insulation is a primary cause of higher running costs, because draughty rooms lose heat much quicker than rooms with insulation up to modern standards. Lower w/m² systems will struggle to maintain the temperature of poorly insulated rooms, resulting in a system that only works as floor heating – a common problem with underfloor heating systems that have been retrofitted in period properties. Higher w/m² systems are better for high heat loss rooms, but the increased amount of cable used for tighter spacing means that the long-term running cost may be more. That being said, choosing a w/m² that is too low is never advised as it will struggle to maintain comfort temperatures, constantly drawing energy as it tries to battle the heat loss of the room. You can also install higher w/m² systems in rooms with standard insulation, and as more of the heat is retained, the room will get to temperature in less time with no real difference in energy costs – in the same way that a higher wattage kettle uses the same amount of energy to boil water as a lower wattage kettle, despite getting the job done in half the time.
Frequency of Use
Many systems are installed with the intention that they will only be used occasionally, or only used at a low level, to take the edge off nippy floors when the weather gets colder. If this is the case for your project, you’ll likely find your running costs much lower than forecasted, as your usage will be infrequent enough to make little difference to your bills. Underfloor heating will always cost a little more if you use it in short bursts, because it will need to heat up from cold every time, so you may find it more efficient to keep your heating on for longer periods of time at a set level. You should also bear in mind how hot you want your rooms when using underfloor heating as a primary heat source. The higher your chosen temperature, the more power your system will need to use to maintain temperatures, and the less often the thermostat will switch your system off.
Finally, another vital aspect you need to be mindful of is what price per kilowatt hour you’re paying for your electricity. The calculations made below were based on the average UK price from February 2015 – 14.05p/kWh – but yours may be lower or higher than this figure. Checking to see whether you can get a cheaper tariff is always advisable, and if you’re going to be using your underfloor heating frequently, it’s definitely worth pursuing to make sure you’re getting the best deal.
We would always advise getting an assessment of your home completed by an energy efficiency expert before purchasing, if you’re unsure whether electric underfloor heating will work as a primary heat source for your rooms.
Potential running costs for a 150W/m² underfloor heating system
To give you a better idea how much yourl system could cost to run, the table below shows the cost in pence to run a typical 150w/m² system in variously sized rooms on an hourly basis.
|Time On (Hr)||1m²||2m²||4m²||5m²||10m²||15m²||25m²|
This table is based on the Thermonet EZ 150W/m² system when used as a primary heat source, providing that a suitable level of insulation has been used. It’s important to note that not all 150W/m² systems will cost exactly the same to run and there will be some variation due to differences in the quality, size and efficiency of the cables used by different manufacturers. The figures provided in this table take into account that the system has been switching off and on again to maintain the temperature set by the thermostat. From this table, you can formulate a rough idea of how much your prospective underfloor heating system will cost per week, depending on the size you’re intending to install and the estimated duration of use throughout the day.
For example, let’s say you’re planning to install an electric underfloor heating system in a kitchen that is 14m² in total with fixtures of 2m² to work around. This would leave an area of 12m² to work with, and when we subtract an additional 10%, we’re left with 10.8m². It’s incredibly important to subtract this 10% because you mustn’t order an underfloor heating kit that is too large – the wires can’t be cut to make it the right size so it’s best to err on the side of caution. We always advise rounding down to the nearest available size kit, which is why we’re going to look at the running cost of a 10m² system. For a primary heat source, the chosen heating kit will need to cover 80% of the area to be heated so a 10m² kit will still be more than adequate for this theoretical installation.
In terms of how often you intend to run your system, let’s assume you will be setting it to come on for one hour in the morning and three hours in the evening. The estimated cost for a 10m² system running for four hours a day is 84.3p, or roughly £5.90, assuming you keep the same routine across the whole week.
If you’re looking to expand that to a monthly figure, this will bring you to around £23.60 or, for a 6-month period, £141.62. This may give you a better idea of whether or not this is an affordable heating option for your household, but for an additional basis of comparison, let’s compare these figures against the running cost of an electric radiator, another popular heating solution.
Cost to run an electric radiator in a 14m² kitchen
When we talk about running costs for underfloor heating, we’re talking about the kit size needed to heat at least 80% of the floor space available when all permanent fittings have been deducted from the total room area. Heating with radiators is entirely different as they use a mix of convection and radiant heat, so for these calculations we need to look at the entire room area.
As we calculate this example, we’re going to use the same conditions that Thermogroup used for their calculations, so the unit price of electric will be 14.05p/kWh. For a room size of around 14m² with standard insulation, we would need an electric radiator with an output of 1200W or 1.2kW. In sharp contrast to underfloor heating, you should always round up when choosing an electric radiator output, but in this example the output we need is handily an exact figure. Continuing on with our four-hour heating period, as per the previous example, we would be using 4.8 kWh of electricity per day. By multiplying this figure by 14.05p/kWh this equates to 67.44p, giving us the daily running cost for an electric radiator in our 14m² kitchen.
Again, if we keep the same heating routine for seven days a week, our total running costs will be around £4.72, or a little over £18.88 for an entire month. Looking at a 6-month period of heating over the colder months, this figure reaches £113.30, making it almost 20% cheaper than the projected running cost for electric underfloor heating system.
Here are those figures compared side-by-side:
|Timescale||Electric Radiators Running Cost||Electric Underfloor Heating Running Cost|
All of the cost figures calculated for the electric radiator were created on the basis that it would be drawing energy for the entire hour it was in use, but it’s highly likely this wouldn’t be the case. Unless you were trying to get a particularly cold room to a high temperature, the radiator might only be using energy a third of the time it’s in use, or possibly even less.
How the difference in heating method can affect the cost
It’s important to take into account that these are two completely different heating methods. Electric radiators heat via a mix of convection and radiation, with much of the heat rising first and then circulating around the room; whereas underfloor heating uses only radiant warmth, rising from the ground up and heating living levels first. As underfloor heating provides heat where it’s needed most it can typically be run at around 2 °C lower than other heating methods whilst still maintaining comfort temperatures.
Another key point is that underfloor heating, by design, is warming a large surface area simultaneously whereas radiators operate from a single point of use in the room. The higher running costs of underfloor heating reflect this but you should keep in mind why you’re probably thinking of installing it in the first place – increased comfort, warm floors and a discreet system that no other solutions can match. It provides a much safer heating method compared to radiators because there are no hot surfaces to come into contact with, and the wide heating area eliminates the possibility of cold spots in the room.
Please remember that these calculations are approximations for illustrative purposes only. Where one home may find their underfloor heating makes a trivial difference to their heating bills, another might see a more marked increase – it’s all about knowing your own unique project parameters and what can affect the efficiency of the system.
Take as much time as you need to prepare and research before you carry out any work, and if you need any further advice or guidance, our friendly team at Heatingpoint is always ready to help.