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It’s important to never miss a detail when it comes to UFH design. A good design will always be bespoke to the project, taking various factors into account to create an efficient solution that effectively heats the property even when it’s a freezing -3°C outside. It guarantees its performance.

What you might not know is that there’s a lot more to UFH design than just the tube drawing – the property is carefully assessed, impacting on the way the system is designed.

In this blog post, we’re taking a look at all the factors that make up a quality system design.

Heat loss calculations

Working out the property’s heat loss is the first step in UFH design. This is an important stage not to be underestimated – if the heat losses are too high then any heating system will struggle to effectively heat the rooms.

Each room experiences a different heat loss, which is why Nu-Heat always calculates heat losses on a room-by-room basis. Factors that can affect a room’s heat loss include:

  • Insulation levels
    The better insulated a room is the lower its heat loss will be. Each element of the room (i.e. walls, windows, roof etc.) will lose heat and the amount lost can be calculated by looking at each element’s u-value. The u-value indicates how well something transmits heat and a lower u-value corresponds to a better-performing building element.
  • External walls and windows
    The number of external walls and windows in a room will affect the heat loss. A room with just one external wall and one double-glazed window will experience far less heat loss than one with 3 external walls and 3 large windows.
  • What’s going on above and below the room?
    If there are heated rooms above and/or below, there will be less heat loss from the room we’re modelling. However, any unheated voids, such as suspended timber ground floors, will mean a higher heat loss.
  • Ceiling heights
    Higher ceilings mean that the UFH has more air to heat in order to meet the desired temperature.
  • Ventilation losses
    All of the above factors are what we call fabric losses, where heat is physically lost through elements of the building such as walls, glass and the ceiling. There are also ventilation losses to consider. In order to make a building a comfortable environment in which to live, a consistent flow of fresh air is required to replace the stale air within the property. Since the fresh air entering the building will be cooler than the warm stale air it replaces, heat will be lost through these air changes.

The fabric and ventilation heat losses are added together to give a figure for each individual room’s heat loss, making it possible to design the UFH to reach the desired temperatures.

Designing the UFH to effectively heat the rooms

In this step we work out how much heat energy the underfloor heating needs to emit in order to heat each room effectively, but before the specific design is decided, factors that dictate the design temperature are also carefully considered:

  • Underfloor heating system
    The heat output of the floor construction must be taken into account in order to design the most suitable solution. For example, an UFH system with a heat output of 80W/m2 will be perfectly adequate for most projects but may not be suitable in a room with large windows and poor levels of insulation.
  • Floor coverings
    Most floor coverings are compatible with UFH, even carpet. However, some conduct heat better than others and sensitive floor coverings such as Amtico and Karndean require a temperature limit that will influence the design.
  • Any unusable floor space
    In some scenarios there may be areas of the floor that cannot be heated, like under kitchen units. This is important because it will affect the amount of usable floor area and as such the amount of UFH tube that can be installed, potentially affecting the overall heat output of the UFH system in that room.

Now we know the heat and ventilation losses, usable floor space and the floor coverings, the actual design of the UFH system begins, taking into account:

  • Tube spacing
    By spacing the UFH tube at closer centres, more can be installed in the room to achieve a higher output.
  • Flow temperature
    A higher flow temperate will increase the heat output. Some heat sources, particularly renewable solutions such as heat pumps, operate more efficiently at lower flow temperatures, so deciding on the flow temperate is always a balance between being high enough to heat the property and low enough to maximise the efficiency of the heat source. Generally the flow temperature for UFH with a boiler is 50-55°C and around 40-50°C with a heat pump.
  • Flow rates
    The flow rate is the speed at which the warm water circulates around the room before returning back to the manifold. The faster the water flows, the more heat energy is being put into the room. However, the design must make sure that the circulation pump can generate enough flow to achieve the desired flow rate around the underfloor heating tube.

And finally, the tube layout drawings

With all of the information prepared and the most suitable UFH system chosen, the designer now works on the tube layout drawings.

The tube layout will meet the design requirements of the property as well as the needs of the customer, e.g. any preference for manifold locations. These drawings make the UFH quick and simple to install, specifying the UFH coil lengths for each room, how these correspond with the manifold and which have thermostats.

To find out more about our design service, 01404 540650

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More about Monika Gontarczyk

As the Design Supervisor here at Nu-Heat, my focus is to make sure our customers get bespoke design drawings for their project to ensure their heating systems perform.

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