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Calculate radiators: that's how much power you need
Calculate radiators: that's how much power you need
Video: Calculate radiators: that's how much power you need
Video: What size radiators do i need ? 2023, February
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Heating must work well, especially in winter. But not only them, but also the radiators that bring the cozy warmth into your living room. Therefore the radiators must be calculated correctly. That means: Before installing, you need to know how large the heating surface should be so that you feel comfortable in your home. How many watts do the radiators need? And how many radiators do you need at all? We explain all of this in this article.

Table of contents Table of contents Calculate radiators: So that you don't sit in the cold

  • Calculate radiators: It is important to avoid these errors
  • Calculate radiators: What does the heating load depend on?
  • How is the radiator calculated?

Table of contents Table of contents Calculate radiators: So that you don't sit in the cold

  • Calculate radiators: It is important to avoid these errors
  • Calculate radiators: What does the heating load depend on?
  • How is the radiator calculated?

One thing right away: the specialist is responsible for the exact calculation of the radiators. So either the architect, the heating engineer or the sanitary expert. Nevertheless, you as the builder are of course interested in how the radiators are calculated and want to know what is coming up financially, where you can possibly save heating costs or why what is set as the specialist does. A professional craftsman will calmly explain each step to you and discuss closely what needs to be done. But it can't hurt to have dealt with the topic in advance and to know what to look out for in discussions with the heating specialist.

Calculate radiators: It is important to avoid these errors

If the radiators are calculated incorrectly, you as the home owner and resident bathe the consequences - physically, but also financially:

  • Too small or too few radiators = your house is cold, although the heating gives 100 percent.
  • Too big or too many radiators = your house is too hot, you are wasting resources and money.

Many small radiators instead of a few large radiators or one large instead of two small radiators - financially, the choice of radiator types makes less than you think. In addition, the physical size - i.e. the length, width and height of the radiator - says less than ever about its performance today. The first thing that matters is that you find the right radiator for your heating in the right thickness for the room - in other words, determine the so-called heating load optimally. And then look for the financially suitable model from various providers and set the heating correctly.

Calculate radiators: What does the heating load depend on?

The topic of radiators is not only mentioned on new buildings, but also when replacing old boilers or when you want to replace radiators. The heating load - that is, the amount of heat required to keep it comfortably warm in the house - depends on how old = " and how big your house is, whether your old building has been renovated and how good the thermal insulation is. This means that the DIN standard EN 12831 with the title "Heating systems in buildings, method for calculating the heating load" is easier to apply to a newly built low-energy house than to an uninsulated old building from the Wilhelminian era.

Because when calculating the heating load to be specified in watts according to this DIN standard, the experts must observe the following points:

  • constant room temperature of 20 ° C with an outside temperature of minus 10 ° C
  • constant room temperature in the bathroom of 24 ° C with an outside temperature of minus 10 ° C.
  • In the event of heat loss - for example due to ventilation or thermal bridges - temperature must be able to be maintained or reached again quickly
  • The heating system runs in the low temperature range - that is, the flow temperature is 70 ° C, the return temperature 55 ° C (according to the Heat Protection Ordinance). If the flow temperature of the heating is kept low, the radiator itself must do its best - in the sense of: the more watts it has to deliver. Flow temperatures of 75, 70 and 55 ° C are currently still common.

If you're already producing enough heat yourself, so you're more of a hotter type, talk to the expert about a general lowering of the room temperature or low-temperature radiators. Some people prefer a general room temperature of 18 ° C and get by with 20 ° C in the bathroom. However, this does not necessarily mean that you can generally reduce the heating load, install smaller radiators or save a large amount of money. On the contrary. A house that is under or wrongly heated has its own problems, such as mold.

Heizkörper richtig einstellen
Heizkörper richtig einstellen

If the radiators are calculated correctly, you will have no problems with a good heat supply even when setting the radiator thermostat.

Photo: iStock / Devenorr

How is the radiator calculated?

The heating requirement for a room can be roughly calculated using the following numbers:

  • 120 to 150 watts per square meter in a non-refurbished old building
  • 60 to 100 watts per square meter in a renovated old building (it depends on the quality of the insulation)
  • 40 to 60 watts per square meter for a new building, thermal insulation regulation 1995
  • 30 to 50 watts per square meter for a new building according to the current energy saving regulation
  • plus 10 percent for the bathroom
  • minus 20 percent for rooms with a sloping roof

This results in the following example calculation for your 25 square meter dining room, which has a heater with 75 ° C flow temperature and 65 ° C return temperature:

25 square meters X 50 watts / square meter = 1250 watts

So you need a radiator in your dining room that fulfills 1250 watts. Or several smaller radiators that reach this number together. On the Internet you will find easy-to-use computers with which you can calculate the radiators and thus roughly determine the heating output. However, these computers do not replace the work of the heating specialists. Also make sure that the radiators you have installed comply with DIN standard 4707 and are suitable for your type of heating.

Do you have a heater with 70 ° C flow and 55 ° C return temperature? Then take the result of the first calculation, i.e. the 1250 watts X 1.24 = 1550 watts. Your radiator needs at least that much power.

With a heating system with a flow temperature of 55 ° C and a return temperature of 45 ° C, calculate the heating capacity of the radiators as follows: 1250 watts X 1.94 = 2425 watts.

Sabrina Deckert

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