What spacing to choose for TC 10 cable (calculating meters per m²)
Why is the laying spacing a key parameter for cable TC 10
The resistive heating cable TC 10 belongs to the most commonly used solutions for underfloor heating in screed on the Slovak market. The number "10" in its designation is not random - it expresses the linear power of the cable, i.e. approximately 10 W per meter of length. This very property is the basis of the entire calculation, which we will examine in detail in this article: how many meters of cable per square meter of floor at a given laying spacing and conversely, what spacing to choose to achieve the desired power on a given area.
The laying spacing (sometimes also referred to as the pitch, laying step or distance between cable loops) is the distance between two adjacent branches of the cable laid in meanders across the floor area. It is not a theoretical parameter - it is a value that directly determines how many watts of thermal power will be available per square meter of floor. If you choose a spacing that is too large, the power per m² will be low and the floor will not be able to cover the heat losses of the room. If you choose a spacing that is too small, you may exceed the recommended power per m² and increase the risk of overheating the screed, degradation of the cable or damage to the surface wearing layer (especially with wooden floors or PVC).
In practice, we encounter the question "what spacing should I use?" in almost every project - from small bathrooms through living rooms to large areas with main heating. In this article, we will show the exact formula, practical tables with ready-made values and a few real examples from everyday installation practice.
Physical principle: the relationship between spacing and power per m²
Imagine a floor on which the cable is laid in regular parallel loops (meanders). If a cable with a power of 10 W/m is laid so that the distance between individual branches is exactly 10 cm (0.1 m), 10 meters of cable will be on each meter of width (since 1 m / 0.1 m = 10). These 10 meters of cable at 10 W/m give exactly 100 W of thermal power on an area of 1 m². This is the basic logic on which the entire calculation is based.
The relationship between the laying spacing and the surface power can be expressed by a simple formula:
Power per m² (W/m²) = Linear power of the cable (W/m) ÷ Laying spacing (m)
For cable TC 10 with a linear power of approximately 10 W/m, this means that it is sufficient to divide the number 10 by the spacing in meters. Equally important is the reverse relationship - the calculation of the length of cable required per m² of area:
Cable length per m² (m/m²) = 1 ÷ Laying spacing (m)
Table of power and cable consumption according to spacing
The following table shows the most commonly used laying spacings for cable TC 10 and the corresponding power per m² and required cable length per m² of area. These values are the basis for planning and it is good to have them at hand for every installation.
| Laying spacing | Cable length per 1 m² | Power per 1 m² (at 10 W/m) |
|---|---|---|
| 6 cm | 16,7 m/m² | 166,7 W/m² |
| 8 cm | 12,5 m/m² | 125,0 W/m² |
| 10 cm | 10,0 m/m² | 100,0 W/m² |
| 12,5 cm | 8,0 m/m² | 80,0 W/m² |
| 15 cm | 6,7 m/m² | 66,7 W/m² |
| 18 cm | 5,6 m/m² | 55,6 W/m² |
| 20 cm | 5,0 m/m² | 50,0 W/m² |
| 25 cm | 4,0 m/m² | 40,0 W/m² |
From the table it is clear that the relationship between spacing and power is not linear in the usual sense - it is inversely proportional. Reducing the spacing from 20 cm to 10 cm (by half) means doubling the power per m² (from 50 to 100 W/m²). Conversely, increasing the spacing from 10 cm to 20 cm means a drop in power by half. This is important to remember - small changes in spacing at low values (e.g. from 8 to 6 cm) have a greater impact on power than the same absolute change at larger spacings.
How to calculate the spacing for a specific area and specific cable
In practice, we usually do not proceed "from the spacing", but the opposite - we have a specific area that we want to heat and we have a specific cable with a fixed power (cable TC 10 cannot be shortened or extended, it is delivered as a ready-made set with a precisely defined power and length). Therefore, it is necessary to calculate what laying spacing to choose in order to evenly distribute the entire length of the cable on the given area.
The procedure is simple:
- We find out the length of the cable in meters (we divide the power of the cable by 10 W/m, which is the approximate linear power of TC 10).
- We find out the clean heated area in m² (the area of the room without edge zones, furniture and fixed obstacles).
- We divide the area by the length of the cable - the result is the spacing in meters, which we then convert to centimeters.
Formula: Spacing (cm) = (Heated area in m² ÷ Cable length in m) × 100
Example 1: Bathroom with 1030 W cable
We have a bathroom with a clean heated area of 10 m² (after subtracting the edge zone of 5 cm from the walls and the area under the bath and WC). We choose HAKL TC 10/ 1030 W 2x prip. kábel. The length of this cable is approximately 103 meters (1030 W ÷ 10 W/m). The spacing is calculated as follows: 10 m² ÷ 103 m = 0.097 m, which after conversion to centimeters gives approximately 9.7 cm. In practice, we would round to a 10 cm spacing, which is a common value for bathrooms, where we want to achieve a pleasant comfortable feeling of a warm floor under the feet.
Example 2: Living room with 1900 W cable
Imagine a living room with a clean heating area of 19 m². We use HAKL TC 10/ 1900 W 2x prip. kábel, which has a length of approximately 190 meters. Spacing: 19 m² ÷ 190 m = 0.1 m = 10 cm. This cable is therefore specifically designed for even distribution on an area of 19 m² with a spacing of exactly 10 cm, which is a typical and recommended spacing for supplementary and main heating in living areas.
Example 3: Smaller area, larger cable - wider spacing
If we wanted to lay the same 1900 W cable (190 m length) on a smaller area, for example 15 m², the spacing would be: 15 ÷ 190 = 0.079 m, that is approximately 7.9 cm. This is already a relatively dense spacing, which increases the power to up to approximately 127 W/m². Such dense laying is used in practice in spaces with higher heat losses (for example, corner bathrooms with a cold external wall) or where we want to achieve a faster temperature rise.
Example 4: Larger area, smaller cable - wider spacing
On the other hand, with the HAKL TC 10/ 2200 W 2x prip. kábel cable with a length of approximately 220 meters, which we wanted to lay on an area of 25 m², the spacing would be 25 ÷ 220 = 0.114 m, that is approximately 11.4 cm. The power per m² would be only around 88 W/m² in this case, which is still sufficient for supplementary heating, but in a poorly insulated building it could already be on the borderline for main heating.
Recommended spacing according to room type and heating purpose
The choice of spacing depends not only on mathematics, but also on what purpose the floor heating is to serve - whether it is the main source of heat, supplementary heating or just to eliminate the feeling of a cold floor. The following table summarizes recommendations based on practice from dozens of completed projects:
| Type of room / purpose | Recommended spacing | Approximate power per m² |
|---|---|---|
| Bathroom - comfort heating | 8-10 cm | 100-125 W/m² |
| Living room - supplementary heating | 12.5-15 cm | 65-80 W/m² |
| Living room - main heating (well insulated house) | 10-12.5 cm | 80-100 W/m² |
| Corridor, entrance hall | 15-20 cm | 50-67 W/m² |
| Winter garden, veranda with losses | 6-8 cm | 125-166 W/m² |
| Tempering of warehouse, workshop | 18-25 cm | 40-56 W/m² |
These values are approximate and in a specific project it is always necessary to start from the heat loss of the room, the thickness of the screed, the type of walking surface and whether there is thermal insulation under the floor. A more detailed procedure for selecting the power according to m² is also discussed in a separate article on how to choose the power of the HAKL TC 10 heating cable according to m².
Edge zones and uneven laying - why you cannot use one spacing for the entire area
In practical installation, it is important to know that the laying spacing is actually calculated for the "clean" heated area, not for the total area of the room. From the total area we always subtract the edge zone (typically 5-10 cm from the walls, perimeter masonry and furniture that is firmly attached to the floor - baths, built-in cabinets, sanitary ceramics). Cable must not be laid in these zones, as it could lead to overheating at the wall or mechanical damage during future work (fixing skirting boards, furniture).
In addition, in practice we often encounter the fact that near the window or the external wall, where the heat losses are the highest, the cable is laid more densely (smaller spacing) and in the center of the room or near internal walls more sparsely. This is called zonal laying and allows for better equalization of the floor surface temperature, since the space near the window naturally loses more heat.
Influence of spacing on surface temperature and walking comfort
The spacing of laying not only affects the total power per m², but also the evenness of the temperature distribution on the floor surface. With a very small spacing (for example 6-8 cm), the heat is distributed very evenly, because the individual cable branches are close to each other and the screed with good thermal conductivity (for example cement screed with sufficient thickness above the cable) distributes the heat well to the entire area. With larger spacings (over 20 cm), "striping" can appear on the surface - areas directly above the cable are warmer than areas between the branches, especially with a thin screed (less than 4-5 cm above the cable) or with walking layers with low thermal conductivity, such as thick carpet.
For this reason, in bathrooms and spaces where we often walk barefoot, it is recommended to choose a smaller spacing (8-10 cm) even at the expense of higher power per m², because temperature evenness is more important here than in storage spaces or corridors, where even a spacing of 15-20 cm is sufficient.
Practical recommendations and common mistakes in the choice of spacing
Over the years of installing resistance cables TC 10, we repeatedly encounter the same mistakes in the choice of laying spacing. Here is an overview of the most common ones:
- Spacing is calculated from the total area of the room including edge zones. The resulting spacing is then incorrect and the cable does not fit exactly on the area, or on the contrary, there is too much unused cable that has to be "densified" in another place, which disrupts the even heating.
- Ignoring the shape of the room. With irregular floor plans (L-shape, recesses) the area must be divided into simpler geometric shapes and the spacing recalculated separately, or calculate with a slight tolerance of ±0.5-1 cm when laying in corners.
- Too dense spacing on a small area with a large cable. If, for example, a cable with a power of 2410 W is to be installed on an area of only 15 m², the spacing comes out to around 6.2 cm, which is on the edge of the minimum recommended spacing for TC 10 and local overheating is a risk. In such a case, it is better to choose a cable with lower power, for example HAKL TC 10/ 1900 W 2x prip. kábel.
- Not respecting the minimum cable bending radius with dense spacing in the corners of the room, which can lead to mechanical damage to the conductive or insulating layer of the cable already during installation.
- No planning of reserve for future obstacles. If in the future it is planned to move furniture or sanitary ceramics, the spacing should also be planned with these areas in mind and a free zone should be left there.
We deal with the most common mistakes in more detail in the article on the most common mistakes in the installation of resistance cables TC 10, where we also discuss other aspects such as fixing, insulation resistance testing and correct placement in the screed.
How spacing relates to the total power of the cable and the selection of a specific model
When selecting a specific model of TC 10 cable from the range (for example HAKL TC 10/ 1100 W 2x prip. kábel or HAKL TC 10/ 2410 W 2x prip. kábel), the laying spacing is also a reverse check of the correctness of the selection. If the spacing you calculate falls outside the reasonable range of 6-25 cm, it is a sign that the power of the cable does not match the area and you need to choose another model or reconsider the heated area.
The practical procedure for selection is therefore two-way - first we roughly estimate the required power per m² according to the type of room (see the table above or a separate article on selecting power according to m²), then we multiply by the clean area and get the required total power of the cable. According to this power we choose the nearest available model from the TC 10 range. In the end, we recalculate the actual spacing according to the exact length of the selected cable and verify that it falls within a reasonable range.
Relationship between cable spacing and installation and fixation
Cable spacing directly affects the method of fixation before pouring the screed. With a denser spacing (under 10 cm), it is necessary to use a fixing strip or a mesh with denser anchoring points, as the cable is more prone to shifting during concreting and the individual branches are close to each other - insufficient fixation may lead to their mutual approach and local exceeding of the safe power per area. With a sparser spacing (over 15 cm), fixation is less critical, but still necessary to ensure the cable does not change its position during workers walking on the floor during the screed pouring.
A detailed procedure for fixation and step-by-step installation into the screed can be found in the articles on the step-by-step installation of heating cable TC 10 into the screed and on how to properly anchor and fix the cable TC 10 before pouring the concrete.
Testing and control after selecting the spacing
Regardless of the spacing you finally choose, it is essential to measure the resistance of the cable before and after pouring the screed and compare it with the value stated by the manufacturer on the label or in the documentation. A correctly chosen spacing ensures the required performance, but if during the installation the cable is mechanically damaged (e.g., pierced during screed compaction or by a sharp fixing strip point), the resistance would change significantly and the cable would not function properly, or there would be a risk of a short circuit. The exact measurement procedure can be found in the article on testing the functionality of the TC 10 cable before and after pouring the screed.
Summary of the calculation procedure
To summarize the entire procedure into a simple overview that you can save and use for each subsequent project:
- Measure the clean heated area (excluding the edge zone of 5-10 cm and the area under fixed furniture).
- Determine the target performance per m² according to the type of room (65-125 W/m² depending on the purpose).
- Multiply the target performance by the area and choose the nearest available TC 10 cable model from the range.
- Calculate the actual cable length (performance ÷ 10 W/m).
- Calculate the actual spacing: (area ÷ cable length) × 100 = spacing in cm.
- Verify that the spacing is within the reasonable range of 6-25 cm, and if necessary, consider denser laying near edges with losses.
Common questions about the spacing of TC 10 cable laying
What is the minimum allowed spacing for TC 10 cable laying?
In most cases, it is not recommended to go below 6-7 cm, as with too dense laying, there is a risk of mutual thermal influence of adjacent cable branches and local overheating of the screed. If your calculation results in a spacing below 6 cm, it is more appropriate to choose a cable with a lower total power or to divide the area into several smaller loops.
Can I use different spacing in one room?
Yes, and it is common in practice. Near edges with cold walls or large window areas, the cable is laid more densely, while in the center of the room or near internal partitions, it is laid more sparsely. It is important that the total length of the cable exactly covers the calculated area without excess or shortage.
What happens if I choose too large a spacing?
The power per m² will be lower than needed to cover the heat losses of the room, and the floor will not warm up sufficiently, or the rise to the desired temperature will be significantly slower. In extreme cases, the difference between the temperature directly above the cable and between the branches may be noticeable when walking on the floor.
Is the spacing the same for all power variants of the TC 10 cable?
No, the spacing is always calculated individually according to the combination of the specific power of the cable (and thus its length) and the area on which it is laid. For example, HAKL TC 10/ 1030 W and HAKL TC 10/ 2200 W will have completely different spacing on the same area, as they have different cable lengths.
Does the thickness of the screed affect the choice of spacing?
Directly no, the thickness of the screed does not affect the mathematical calculation of the spacing, but it affects how noticeable the uneven temperature distribution will be with larger spacing. With a thinner screed (under 4-5 cm above the cable), it is more appropriate to choose a smaller spacing to allow the heat to spread better across the area before it reaches the surface.
Do I need to calculate a reserve cable for the connection to the thermostat?
The cold supply cable (connector between the heating part and the thermostat) is not included in the spacing calculation, as it does not emit heat. Only the length of the resistive (heating) part of the cable is included in the area calculation, which is stated in the technical parameters of the specific model.
Conclusion
The spacing of the TC 10 cable is a simple but crucial calculation that determines whether the floor heating will function efficiently, evenly, and safely. The basic formula - the power of the cable divided by the spacing in meters - can be calculated by anyone who knows the area of the room and the power of the selected model. It is important not to forget the edge zones, to adjust the density of laying according to the type of room, and always to verify that the calculated spacing is within the recommended range of 6-25 cm. When selecting a specific model from the range of resistive TC 10 cables, it is worth recalculating the spacing before ordering to avoid situations where the cable does not fit the area exactly or is laid too dense or too sparse compared to the recommendations. If you are unsure about choosing the correct power for your area, we recommend reading our article on how to choose the power of the HAKL TC 10 heating cable according to m², which continues on this topic.
Do you have a question about this topic?
Not sure how to decide or dealing with a specific situation in your home? Write to us - we are happy to help.