Heated floor power - calculations for electric and water heating types

Modern underfloor heating systems entered people’s lives not so long ago, but they took root immediately.The advantages of this type of heating are felt as soon as you start using them. And it doesn’t matter whether it’s an additional heating network or the main one.

But you need to choose the right characteristic - the power of the heated floor. It is determined by the manufacturer taking into account the design of the heating element.

Average temperature of underfloor heating

There are several legislative documents that define the so-called permissible and optimal microclimate indicators. One of them is SanPiN 1.2.3685-21. It states that an acceptable indicator is one at which people no longer feel comfortable. But there is no harm to health.

The optimal indicator is the one at which comfort is reduced by only 20%. That is, a person does not spend any serious expenses on thermoregulation.

The optimal parameter according to GOST has exact temperature limits:

minimum – +12 ℃;
maximum – +28 ℃.

The exact temperature value depends on two factors: season and type of room. The latter is, for example, a bedroom, living room, corridor, bathroom, etc.

Doctors participated in the development of SanPiN, who, knowing human physiology, accurately established a comfortable temperature in living quarters according to the seasonal factor:

in summer 22-25 ℃;
in winter 20-22 ℃.

Now by type of room:

bedroom – 18-20 ℃;
living room – 19-21 ℃;
children's room at night - 18-20 ℃, during the day - 20-23 ℃, for infants not lower than +20 ℃;
toilet – 19-21 ℃;
bathroom – 24-26 ℃;
kitchen - 19-21 ℃, if you cook often, then 17-18 ℃.

Therefore, the temperature of the heated floor may be different in each room. But there is an average value, which is determined by SNiP - +26-27 ℃. In this case, the indicator is lower than the value of the radiator temperature regime. Hence the savings that people talk about when it comes to heated floors. By the way, Europeans have different standards - +21-22 ℃.

What affects the power of a heated floor?

There are many factors influencing the power of a heated floor:

Climatic conditions of the region.
Is the house insulated or not?
Number of windows in the room.
Warm floors are the main heating system or an additional one.
Dimensions of the room and its purpose.
Type of flooring.

Everything is clear with the region - the further north you go, the more power you need to choose heated floors.

Yes, completely throughout the entire apartment/house.

Yes, partially. In some rooms.

100%

No, but I plan to do it during renovation.

Voted: 1

Thermal insulation of the room

Thermal insulation is more difficult. After all, the main factor influencing the choice of power is the heat loss of the building. The larger they are, the more powerful the heating should be. This means that energy costs will increase, for which you will have to pay more. For example, the walls of a panel house have heat loss within 50%, which is completely unacceptable in modern realities.

Therefore, it is recommended to insulate all building structures of the house or increase their thickness. The first option is both simpler in terms of construction and cheaper. Mandatory conditions are the installation of insulated entrance doors and multi-chamber plastic or wooden windows.

The amount of the latter does not greatly affect heat loss, because this figure is low compared to other elements of the building. It accounts for 10% of total losses.

Is the main source of heating

If heated floors are the main heating system, then the recommended power for residential premises is 160-200 W per m². If this is an additional system, then 110-140 W. If there is an unheated volume below, then the figure increases to 130-160 W per square meter. In wet rooms, the power increases to 160-180 W.

There is one point that not everyone pays attention to. It is designated in SNiPs. If the area on which it is decided to lay heated floors is less than 70% of the total area of the room, then a heating system of this type can only be used as an additional one.

For example, if the area occupied by furniture is 35%, then the power of the installed heated floor should be calculated taking into account the above stated requirement. In numbers, it should not go beyond 110-140 W/m².

Type of flooring

There are difficulties in choosing the power of a heated floor depending on the finishing material of the floor base. It depends on the thermal conductivity of the cladding. For example, for ceramic tiles this parameter is 0.5-0.9 W/m K. For linoleum - 0.2, for laminate - 0.1.

That is, the higher the value, the more intensely the material transmits thermal energy through itself and the heating works more efficiently.Accordingly, the power should be less. In this regard, ceramic tiles win and lose laminate.

Room type and size

Specific power taking into account the types of premises per 1 m² of area:

living rooms and kitchen located on the 1st floor of the house – 140-150;
living rooms and kitchen located on the 2nd floor and above – 120-130;
bathrooms and toilets – 140-150;
glazed loggias and balconies – 180-190.

All the above power values are given without taking into account heat losses. To establish the exact parameter, professionals with special equipment are invited.

Type of installation

Regardless of the type of heated floor, it is laid on a prepared base. It must be smooth, repaired, and insulated. To the water type, another layer is added - a waterproofing one in the form of a membrane laid on the base.

The installation of the heating network itself is carried out using three technologies:

Ceramic tiles are mounted on top of the heating element using an adhesive composition.
A cement-sand screed is poured over the heating element. The thicker the latter, the longer it takes to warm up. Accordingly, there will be an overconsumption of energy for some time.
Dry technology. It is used when finishing the floor base with laminate. Here it is necessary to understand that the laminate is directly laid on the heating system only if the latter is an infrared film floor. In other cases, a flat solid layer of plywood, OSB or chipboard is installed. There is another cheaper option - laying the heating element in pre-prepared grooves made in the floor.

Thermostat type

The main characteristic of the thermostat is the switching power, which varies in the range from 3 to 3.5 kW.The exact value can be found in the product data sheet.

This thermostat parameter depends on the power consumption of the heated floor. Here it is not specific, but general. That is, the one that is consumed by all square meters.

For example, the total area covered by the heating element is 20 m². The specific power on heated floors, also known as the rated power, is 120 W for additional heating, 180 W for the main heat source.

Now you can calculate the total power:

20x120=2400 W or 2.4 kW;
20x180=360 W or 3.6 kW.

If the selected thermostat has a switching indicator of, for example, 3.35 kW, then it can be installed in a system of underfloor heating that operates only as an additional heating network.

How to calculate the power of a water heated floor

It is not difficult to calculate the power for warm water floors. To do this you need to know four indicators:

the area on which the heating element is laid;
coolant flow;
with what step the heating element is laid;
heat losses of the room.

Planning

If a water-type or infrared rod-type underfloor heating system will be installed in the rooms, then there is no need to draw up a plan. The reason is that plastic pipes and carbon rods easily carry loads from heavy furniture, musical instruments and household floor appliances.

A plan is needed if other types are used: cable, cable on mats, film infrared. Therefore, a room is drawn to scale on a sheet of paper with the exact location of furniture and other heavy objects. Anything that remains free of them must be covered by the heating element.

Determination of area

Everything is clear with the water and rod options.They will cover the entire floor base with a distance of 10-15 cm from the walls. You will have to tinker with the other three options. To do this, the plan drawn on paper, or rather the surface free from furniture, must be divided into regular shapes. The easiest way is if these are rectangles, the area of which is equal to the multiplication of their sides. The areas of all the figures are added up to create an area for heating.

You can do the opposite. Calculate the total area of the room. Then separately calculate the area of furniture and other items. Sum up the latter and subtract the resulting result from the total indicator.

Heat loss calculation

There is a formula by which heat loss is calculated - Q=ST/R, where:

S – room area;
T – difference between internal and external air temperatures;
R – thermal resistance with unit of measurement m² K/W.

The last characteristic is not thermal conductivity.

This formula is used to calculate the heat loss of building structures: walls, floors, ceilings, windows and doors. Then the obtained values are summed up.

Eg:

ceiling height – 3 m;
room width – 5 m;
its length is 10 m;
windows measuring 1.5x1.4 m;
temperature inside the room is +20 ℃, outside -20 ℃.

First you need to calculate the area of each building structure:

walls: (5+10+5+10)x3=90 m²;
floor and ceiling separately: 5x10=50 m²;
window: 1.5x1.4=2.1 m².

Total area of building structures: 192 m².

The coefficient of thermal expansion is a tabular value. Depends on the thickness of the materials used and their thermal conductivity. For example, floors made of cement screed with a thickness of 10 cm and insulation thickness - mineral wool - 5 cm:

R screeds: 0.1/1.75=0.057 m² K/W;
R mineral wool: 0.05/0.037=1.35.
total R – 1.4 m² K/W.

And in this way all building structures are calculated, the values of which are summed up.

You can calculate the heat losses of each structure separately. Same floors:

Q=90x40/1.4=2571 W or 2.57 kW.

The obtained values of heat losses for each building structure are summarized into one indicator.

Coolant flow

This calculation is carried out only for a water-based underfloor heating system. It is made in order to correctly select the circulation pump that drives hot water through the hollow pipes of the system.

For this, the formula is used: G=0.86Q/∆t, where:

0.86 – heat capacity of water;
Q – thermal power in W;
∆t – temperature difference in the return and supply circuits.

Laying pitch and contour length

Here we need to talk only about water and electric cable heat fields. The latter has a wider selection, which depends on the power of the heated floor per 1 m².

Eg:

the laying step is 7.5 cm under the screed, for which a 130 W cable is used;
step 12 cm – 150-160 W;
step 15 cm – 180-200 W.

If underfloor heating is used as an additional heating circuit, the power can be reduced. The same reduction can occur if the heating element is placed under the ceramic tile directly on the adhesive.

With a pipe it's a little different. Here the dependence is not on power, but on the diameter of the pipe. For example, 16 mm:

16 mm diameter pipe is laid in 15 cm increments;
if the heat loss in the room is large, then the step is reduced to 10 cm;
The step can be increased to 20 cm if underfloor heating is not the main source of heat.

A larger pitch can be used, but not in houses and apartments. It is used at industrial facilities when laying pipes with a large diameter.

To calculate the length of the water circuit, the formula F=S/h is used, where:

S – heating area;
h – step of laying the heating element.

If the length of the pipe circuit exceeds 100 m, then it must be divided into several sections with a thermostat, temperature sensor and circulation pump connected to each section.

Floor power

This value in water heated floors is not very large. It varies from 40 to 150 W per square meter of surface. But it is necessary to take into account that the distribution of the coolant, and therefore the heat, must occur evenly throughout the entire circuit.

There is such an indicator - the density of thermal water flow. This is what is taken when choosing a circulation pump. To calculate its value, use this formula Q=q/S, where:

q – heat loss;
S – heated area.

Boiler performance

It is rare when more than one heating boiler is installed in a house. Therefore, its power is determined taking into account the power of all heating systems, including heated floors. That is, for the calculation, the power values of each room are taken and summed up.

An additional 15% is added to the resulting value. This is a reserve that compensates for the resource costs of the boiler itself if it operates under the maximum rated load.

You don’t have to carry out complex calculations, but take as a basis the ratio: 10 W of thermal energy is consumed per 1 sq.m of area. For example, if the total area of the house is 100 m², then a 10 kW boiler is used to heat it.

Circulation pump

The longer the heated floor circuit, the more powerful the pump you need to buy. You can use the special formula Q=0.86 P/∆t, where:

0.86 – thermal conductivity of water;
P – boiler power in kW;
∆t – temperature difference in the supply and return circuits.

Let's calculate the power of an electric heated floor

Before you start calculating an electric heated floor, you need to accurately determine several parameters of the heating system:

Warm floor will be used as the main source of heat or as an additional one. That is, its power will be 150-200 W/m² or 110-150 W/m².
What are the heat losses? If they are more than 100 W/m², then it cannot be used as the main one.
Warm electric floors are installed only on an area free of furniture.

Formula for calculating power P=PnS, where:

Pн – heating element power;
S is the area of the room free of furniture, floor-standing household appliances and floor-standing musical instruments.

The first characteristic is indicated by the manufacturer in the product labeling. For example, in the photo below you can see that the cable power is 24 W/m. That’s what it says there – 24W/M.

Knowing the cable laying pitch, you can determine how much heat it will produce per 1 m². For example, if the laying step is 15 cm, then 6 contours will be laid in one square meter. This means the total power is 24x6 = 144 W/m².

Knowing the last parameter and the heated area, you can accurately calculate the total required power of an electric heated floor. That is, multiplying two characteristics among themselves.

Which underfloor heating system to choose

If we talk about apartments, then there are only electric heated floors. It is prohibited to connect the water system to the heating of the house. You can install a separate boiler or mount a complex water distribution unit. But all this is difficult, unprofitable and labor-intensive. Therefore only electric type.

Any of the above can be installed in a private home.It is better to give preference to a water one, because it is simply connected to the heating boiler through a coolant distributor.

Determining the temperature in the room

According to standards, the temperature in the room must be measured at six points. Height 20 cm and 150 cm from the floor. Horizontally - in two opposite corners and in the middle of the room. Measurements are carried out for 10 minutes at each point.

The average value of three measurements is determined at the level of 20 cm, and exactly the same at the level of 150 cm. In the first case, the temperature should be within +27 ℃, in the second not lower than +18 ℃.

How to reduce consumption costs

Reduce energy consumption Can. To do this, you will have to do several important things:

Carry out insulation of all building structures, accurately selecting thermal insulation material taking into account its thickness or thermal conductivity.
Install windows and doors that belong to the insulated category.
Use materials with high thermal conductivity for finishing the floor base.
Correctly set the temperature on thermostats taking into account the time of day.
Connect a double tariff to your home, which allows you to use electricity at night with a halved payment.

If you decide to install heated floors in a house or apartment, you must first calculate their power. If this is not done or the choice is made “by eye”, then there is a high probability that energy overuse will occur. Plus - the microclimate in the rooms will not be comfortable.

How much does a heated floor consume? Electricity consumption of a heated floor: video.

If someone has already had experience choosing a heated floor based on power, tell us about it in the comments. Save the material in bookmarks so as not to lose useful calculation formulas.