How much insulation is required for underfloor heating systems?

Overlay systems, because of their requirement to be low profile, have a reduced ability to provide resistance to heat penetrating the floor beneath resulting in precious energy being lost to the floor below. Some installations go in with no insulation but a minimum of 25mm would make a huge performance difference to heat loss.

Conversely, with greater floor depth the installer of a screed system in a new construction has the luxury of installing very high levels of insulation to stop heat being wasted. Insulation levels on the ground floor of homes can reach 100-125mm. Beyond that, the benefits of thicker insulation diminish rapidly.

What are the thermal mass benefits of underfloor heating systems?

All manner of pre-cut thermal board solutions are available for overlay underfloor systems to use. These are often high density and very expensive to purchase, but they are thin! Whilst these boards that the overlay system pipes are clipped into have some thermal mass, their ability to retain heat once the underfloor heating is switched off will be markedly reduced compared to a thicker and more massive liquid or sand/cement screed solution. Simple intuition, let alone physics, tells us that by installing a large quantity of screed around the underfloor heating pipes this mass will hold heat better and reduce unwanted floor temperature fluctuations.

A balance between practical thermal mass benefits and floor construction thickness need to be analysed during the design phase to find the right answer for your application.

How much pipe is required for underfloor heating systems?

For efficient low temperature underfloor heating systems, pipe spacing is proportional to ultimate efficiency. The ability to minimise pipe spacing and change pipe detail near key building openings is common sense and will provide more thermal output from a square metre of floor area for a given flow temperature. 100-150mm pipe spacings are the norm for heat pumps and 200-250mm pipe spacings for gas boilers can result in a generous heat output of 100W/m2 for a tiled floor.

Screed systems allow almost infinite design flexibility but with pre-machined boards this is simply not possible and heat pumps especially have to work hard to operate successfully with overlay systems. So called ‘egg-box’ overlay system boards do allow much more flexibility and for the installer to route pipes more flexibility as the project dictates.

How hot does the water for underfloor heating systems need to be?

The small bore pipes used by overlay systems (nominally 10-12mm) require water at 45-55ºC to create suitable levels of heating during winter. Alternatively, screed systems can run at much lower temperatures 30-40ºC and their larger pipe diameters (nominally 15-16mm) allow slower water flow to enable better heat transfer to the room. Lower temperatures for any heating system, but particularly heat pumps, will result in lower running costs too.

How much do the different types of underfloor heating systems cost?

The all-in costs for the two different systems are pretty stark. Including materials (not insulation of floor finishes), labour and VAT, screed underfloor heating prices come out around £40/sqm. In comparison, overlay systems cost around £70/sqm installed.

If you have any questions about underfloor heating systems, please don't hesitate to contact the Mesh team today.