How much does underfloor heating cost to run?
Updated: Oct 12
The honest answer has two parts: the arithmetic, which is simple, and the variable that most articles skip, but is the biggest factor that actually decides your bill.
Lets start with the arithmetic. An underfloor heating element is rated in watts. A 6 square metre bathroom at the 150W per square metre Heatwell recommends that a 900W element is installed under tile — the same 900W element that draws 3.91 amps and measures 58.78 ohms, which is the figure your electrician will check. 900W is 0.9 kilowatts, so every hour that element is actually on is drawing power cost of 0.9 multiplied by your electricity rate. New Zealand residential rates in 2026 run from around 35 cents to just under 49 cents a kilowatt hour depending on where you live. At 38 cents, an hour of element-on time in that bathroom costs about 34 cents (0.9 x 38), or 5.67 cents per square metre per hour (34/6).
Now the part that matters. Your floor is not drawing power the whole time it is switched on. The thermostat brings the floor up to the temperature you set, then cuts power and only calls for more power when the floor cools. The thermostat decides your on and off rules. The proportion of time the element actually runs is what decides your bill, and it varies enormously.
A floor laid over insulation board, in a room with a closed door, might call for power well under half the time once it is up to temperature. The same cable laid straight onto an un-insulated concrete slab that is pushing heat downwards into the ground continuously and will run far more.
The practical guidance: for a bathroom on under tile and slate underlay, insulation board, or a newer insulated concrete pad, budget on the order of a dollar to a dollar and a half a day through the coldest months and less in the shoulder seasons. You can double the cost for an un-insulated concrete pad found in older NZ homes.
For a whole living area, the number scales with the heated area. Multiply the square metres by the cost per square metre. Using the example above, if you have a 20 square metre room that has 150W per square metre at 5.7 cost cost per hour would be around $1.14 per hour over an good quality sub-floor.
What can I do to save on the electrical cost?
A thermostat schedule saves more money than anything else you can do. Schedule the floor to come up to temperature before you need it and drop back when you do not, rather than running it all day. As with all heating, the golden rule is to have it running when you are likely to use it.
Most thermostats are able to be set for two time periods a day. For example: If you are usually up at 7am, schedule the heating to come on at 6am. If you usually leave the house by 8.30 have the heating turn off at 8.30. You usually get home at 6pm? Schedule the heating to come on at 5. You are usually in bed by 10.30? Schedule the heating to turn off at 10.30.
Please note that heating over a poorly laid sub-floor like an un-insulated concrete pad will take significantly longer to heat up that a well laid modern floor. You will need to schedule heating to come on earlier. How much earlier? Only trial and error will teach you the settings.
I have an older house with an older un-insulated concrete pad. What can I do?
If the underfloor heating is already installed there is nothing you can do. You will need to learn where to schedule the thermostat for your preferences. Unfortunately you will need to suffer the extra electrical cost.
If you are about to do a renovation on a property with an un-insulated concrete pad then insulation board is a must. Insulation board is an additional installation cost. However, the power savings the insulation board will provide is well worth the cost.
How does electric underfloor heating cable work?
Electric underfloor heating cable is a specially designed to heat through resistance. It is the same principle as an electric oven or toaster. Unlike the electric oven, the switch for underfloor heating, the thermostat, cannot regulate the amount of power going through the cable. Underfloor heating is either fully on or fully off - just like the toaster.
How does the thermostat work?
The thermostat is a glorified switch. The thermostat is creating the rules for how underfloor heating is turned on and off. Most thermostats have a manual option and a programmed option. The manual mode allows for continuous operation. The programmed mode allows rules to be set on for off and on times.
Most thermostats have a temperature differential built in that makes sure the underfloor heating is not on continuously. For example, you have set your maximum temperature at 26 degrees. The thermostat will allow the floor to heat up to 27 degrees, then let the temperature to drop back down to 25 degrees before clicking back in. This is a 1 degree differential either side of the maximum temperature.
The article is well structured and the ideas are expressed clearly. The explanations are accompanied by practical examples that aid understanding. I have already shared this article with some colleagues who work on the same topic. Usually it is not simple to find information so well organised on this topic.
The analysis of electricity costs for underfloor heating reveals significant insights. The formula provided is a useful tool, but the assumptions made can greatly impact accuracy. Considering real-world factors like run time is crucial. Additionally, understanding the specific wattage for different materials, such as those installed by Heatwell, helps consumers like Leon make informed decisions regarding energy efficiency and costs.
The discussion around the costs associated with underfloor heating is quite intricate. It’s interesting to note how different wattages impact energy consumption, which can vary widely based on installation types. Understanding the formula is crucial for accurate budgeting. However, I wonder how often real-world factors, such as insulation quality, affect the calculation of Wildz in this context? Balancing theoretical costs with practical use will be essential for homeowners.
The article provides a nuanced view of energy costs associated with underfloor heating, particularly highlighting how size and wattage translate into consumption patterns. The formula offered is practical but heavily relies on assumptions. Understanding electricity costs is essential for homeowners. As we explore energy efficiency, this insight could become a Kiwi Treasure for many considering underfloor heating systems.