The builder’s take: why underfloor heating is worth considering

In the past 20 years there have been a lot of advances in technologies, materials and regulations and most are related to energy efficiency.

Heating our homes effectively and then keeping them heated are key issues. Weather-compensated boilers, heat pumps and airtightness are all buzzwords, so for anyone embarking on a renovation or a new build, what heating system to go for can be a quandary.

One of the major changes is how underfloor heating (ufh as builders call it) has advanced. It is not a new notion – it can be traced back to Roman times where the stone floor of a villa was raised on brick piers and hot air from wood fires circulated below it.When I started out, in the late 1990s, it was still a fairly innovative approach. Back then, I saw elaborate snake patterns of pipework getting buried under 125mm of concrete. With this depth of concrete to heat up before it could even start to heat the room, it was never going to be much of a hit.

As a result, ufh has had a dubious reputation, but with excellent advancements in insulation and floor screeds it’s a very different story now.Liquid screeds give the option of a screed depth of as little as 40mm – something which can’t be achieved with concrete or sand and cement – giving a warm-up time of less than one hour. Liquid screeds offer better thermal conductivity than concrete too, and with houses now being super-insulated, the low output from ufh works really well. Advancements in the heat source, such as weather-compensated gas boilers and air-to-water heat pumps make ufh a more efficient option.

Even heat

Perhaps the biggest benefit is that an underfloor heating system heats from the floor up which is more effective in supplying an even heat over the whole room.

A radiator sends out a really intense heat in one location, rising straight up to the ceiling and then convecting it around the room. This even heat creates a more ambient atmosphere than that provided by radiators.

With radiators, a room thermostat could read an air temperature of 22 degrees, but the temperature at ceiling level could be nudging a tropical 30 degrees, while the floors might remain a chilly 15 degrees, with tiles feeling cold underfoot.

A further consideration is space: ufh stops wall space being taken up by radiators. This can be especially important in a kitchen area where apart from the walls taken up by the kitchen units, we are now seeing a lot of glass in these rooms too – entire walls taken up with windows and glazed doors – leaving a radiator to be shoe-horned in somewhere not at all desirable.

And unless you’re willing to part with a shed-load of money for designer rads, they don’t tend to be the prettiest of interior features. Now the temperature of water required to run through your network of underfloor piping is much lower too.

Stephen O’Kane from Greenhouse in Deansgrange, Co Dublin says that the water only needs to be heated to 35- 40 degrees compared to 60 degrees for a radiator. He says “a new-build BER A3 house of about 150sq m with an air to water heat pump, ufh on the ground floor and low temperature radiators upstairs, can now be heated and have 24/7 domestic hot water for approximately €450 per year”. Not bad.

Is carpet an option?

The current thinking is to run underfloor heating throughout the downstairs, while putting low temperature radiators upstairs. Ufh can run upstairs too, but timber and carpet are not great conductors of heat and forming screeds upstairs will be costly.

For floor coverings, tiles, stone or similar are generally accepted as the best. They absorb heat rather than insulate and allow heat to radiate into the room. Wood will tend to insulate and reduce efficiency, but thinner engineered boards have little noticeable impact on heat output. Solid timber is notoriously tricky with ufh and would need to be acclimatised for at least a month. I would advise to avoid it, but ask your supplier for advice.

Carpet is generally considered a no-no, but the Carpet Foundation in the UK carried out some research in conjunction with the Underfloor Heating Manufacturers Association which seems to show that some carpets can be used with ufh.

Recently I’ve noted a rise in popularity in polished concrete floors.These really can’t be laid any less than 75mm deep, making them a very inefficient companion to ufh.

Rough estimates on design, supply and installation of your underfloor heating system, based on a 100sq m area, will be about €27-€30 per metre. A 40mm screed will typically be approximately €19 per metre for this area. You will also need your heat source, such as a boiler or heat pump, and your cylinder.