How to properly design underfloor heating at home?

Underfloor heating will only function properly if it is properly designed and executed. Where to start?

Naturally, it is much easier to create an efficient underfloor heating system in a newly built house. First, decide whether you aim for water underfloor heating or electric. Here, the main issue is the energy source. In this article, we will focus on traditional water underfloor heating, in which heating loops are hidden in the concrete floor, filled with warm water.

Let's get started

Good substrate insulation is essential. In rooms where we plan underfloor heating, the ceiling should be high enough to allow us to lay layers of styrofoam insulation and then lay the loops + a layer of screed, which will function as the underfloor heating. If we buy a ready-made house plan with underfloor heating planned, it should already be included in the project.

Planning underfloor heating - how to lay heating loops?

Loops are nothing more than pipes through which hot water flows, or more precisely, warm water (due to the fact that properly designed heating of this type does not require a medium with a temperature greater than 28-35 degrees Celsius). These pipes are most commonly made of plastics such as cross-linked polyethylene (PE-X), so they are often colloquially called PEX.

Pipes are not laid out randomly and uniformly. The farther from the boiler room or heat source (i.e., boiler, fireplace, heat pump, etc.), the cooler the water in the pipes will be, as it loses its heat to the concrete screed, heating the floor. Therefore, closer to the boiler room or heat source, we can, and maybe even should, lay the loops less densely than in more distant rooms.

Many professionals, not without reason, advocate laying loops starting from the wall most exposed to heat loss. This is the wall with large windows or the wall on the shaded or north side.

What should be the distance between heating pipes in underfloor heating?

It is often said that they should be laid at distances from each other from 10 to 35cm. In zones closer to the edges, i.e., near internal walls, it is worth laying them more densely because the floor cools down the fastest there. However, loops should be at least 10-15cm away from external walls (a value assumed for insulated buildings).

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Where not to lay underfloor heating loops?

It is worth sketching out the potential layout of furniture, especially built-in kitchen or bathroom furniture that we will not be moving before laying the loops. Laying loops under them is not recommended; efficient underfloor heating does not heat the bottom of our cabinets or drawers. This is inefficient heat, which over time only distorts or warps the shape of our furniture.

Another common mistake is installing loops under the shower in close proximity to the linear shower drain (if we have one). Naturally, we can lay loops under the shower, and the warm floor in this place will increase our comfort of using the bathroom. However, if the heating pipe is laid directly near the shower drain siphon - it may dry out, so there will be no water in it, and we will feel odors coming back from the sewage. (This applies to so-called wet siphons).

We have laid out the underfloor heating network - what now?

In the next step, there is screed. It is assumed that it should be 7-10cm thick (we are talking about the layer that will be laid on the bottom insulation layer). If we hire a professional company with experience for screeds, we can expect them to know what they are doing, in line with the art. However, it is worth asking, and if the thickness of the screed deviates from the norm - we should expect a clear answer as to why and consult the answer continuously with other professionals. Trust, but verify - this is the best solution in construction. However, there may be deviations from the given thicknesses, so remember that the company performing or the designer ultimately takes responsibility for the work. Check it, but remember that at least he should have experience. An example of a deviation from the thickness of 7-10cm is the planned layer of stone on the floor, e.g., in service facilities such as banquet halls or hotels.

Choosing an underfloor heating manifold - at what stage?

If we are not in a hurry with construction and we are building at ease - it is worth waiting to choose the manifold until this moment. When the PEX pipes are already laid - then we are 100% sure how many loops (circuits) there are, i.e., we have the basic information - how many circuits the manifold needs to have. Sometimes at the planning stage, we have certain assumptions that we change during execution.

However, if we want to have the equipment purchased earlier to avoid unnecessary delays - we can, in cooperation with a specialist, draw the loop layout on the building plan and based on this, determine how many circuits our manifold will need. If we have any doubts - we can always purchase a manifold with 1 extra circuit than we plan. It will simply be blocked and unused - if we decide on a smaller number of loops. Purchasing a manifold equipped with an extra section costs an additional 50-70 PLN, which, in the scale of the entire investment, will not strain us financially. However, remember that a manifold with an additional section is also longer by about 5-7cm. It must fit in the place intended for the manifold.

However, the selection of the right underfloor heating manifold does not only involve the number of sections. It is a broader issue - which we addressed in another thread, but the most important thing is the equipment of the manifold.

Check out the NORDIC TEC manifold catalog.