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Sizing oil-filled
electrical radiators
The tables below contain rules of thumb for how many watts are reasonable per square meter depending on where in Sweden you live and how old the house is. The values apply to normal ceiling height, ie. 2.40–2.50 m. To calculate the amount of power needed for other ceiling heights, you can expect a power requirement of 30 W per cubic meter.
Also, to consider when sizing a radiator is not necessarily to choose the smallest possible one that meets the rules of thumb. One should consider taking a size larger as the operating cost is the same as for a smaller one with the same heat demand. The difference is that the large radiator can contribute more heat during the coldest days.
How to easily calculate your home's total heating needs
Temperature zone 1
| Built (year) | Watt per square meter |
| Earlier than 1960 | 98 |
| 1960-1975 | 88 |
| 1975-1980 | 78 |
| Later than 1980 | 65 |
Temperature zone 2
Table 2 shows the rules of thumb for how much power is required per square meter in temperature zone 2. All these values are for houses without exhaust air ventilation. If the home in question has this then the rule of thumb in this temperature zone is to add 22 W per square meter.
| Built (year) | Watt per square meter |
| Earlier than 1960 | 89 |
| 1960-1975 | 80 |
| 1975-1980 | 71 |
| Later than 1980 | 59 |
Temperature zone 3
Table 3 shows the rules of thumb for how much power is required per square meter in temperature zone 3. All these values are for houses without exhaust air ventilation. If the home in question has this then the rule of thumb in this temperature zone is to add 20 W per square meter.
| Built (year) | Watt per square meter |
| Earlier than 1960 | 84 |
| 1960-1975 | 76 |
| 1975-1980 | 67 |
| Later than 1980 | 56 |
Temperature zone 4
Table 4 shows the rules of thumb for how much power is required per square meter in temperature zone 4. All these values are for houses without exhaust air ventilation. If the home in question has this then the rule of thumb in this temperature zone is to add 18 W per square meter.
| Built (year) | Watt per square meter |
| Earlier than 1960 | 72 |
| 1960-1975 | 65 |
| 1975-1980 | 58 |
| Later than 1980 | 48 |
To consider when sizing a radiator
There are certain situations where a liquid-filled electric radiator is more suitable than other alternatives. An example is an extension. The original home may have a hydronic system which means that new pipes must be drawn. To avoid this, electric radiators can be placed in the new, extended part of the building.
In some cases, there are no other heating options, for example in many summer cottages. Geo-heating is expensive to install, and district heating is only used in densely populated areas. Using biofuel requires a boiler and is therefore difficult to install after the housing has been completed. The boiler also requires some maintenance in the form of soot. In this case, an electric radiator is the perfect solution, provided the summer cottage has electricity.
It may also be that a home needs complementary heating during the coldest days of the year. An electric radiator is flexible, ie. you get the heat where you want it, and consume no electricity when it is switched off, it therefore offers a cost-effective complement to the existing heating system.
The fact that the electric radiator is a good complement to increase the comfort of passive houses has also been demonstrated in tests that have been carried out and presented on eg. Passive House Conference in Gothenburg 2013.
If you need help finding the right oil-filled electric radiator or require assistance for the sizing, don't hesitate to contact us. Our heating experts are happy to help.