Your Flooring Matters

Your Flooring Matters.

Can we have underfloor heating with timber flooring? Yes, with underfloor heating (water based & heat pump powered).

Do we need underfloor heating in carpeted areas? Of course we do. No one wants cold bedrooms. The priority of underfloor heating is heating the rooms, then the floor surfaces. Heat will come out through the carpet but the effectiveness will depend on the specific product and underlay.

Please ensure your flooring suppliers know that underfloor heating will be installed.

Most floor coverings can be laid when underfloor heating is installed. However, thick carpet underlay should be avoided – heat is effectively trapped in the slab which results in lower efficiency and therefore higher running costs.

Also avoid any type of underlay with a reflective foil. The foil is designed to stop some energy from the room going into the floor (by reflecting it back) – with underfloor heating it will try and reflect back into the floor. The overall result will be higher running costs as the temperature will need to increase in the floor to jump the foil.

If you’re after a carpet underlay that has been designed with underfloor heating in mind, local Christchurch company has an option for you.

The UK standard for floor coverings is that they should have a combined thermal resistance of no more than 0.15m2K/W.

What this means in practice is that tiles and polished concrete (for example) are very good. Timber overlaid or glued down is perfectly acceptable (but ensure the concrete is thoroughly sealed before gluing down). Vinyl is also fine – but ensure in all cases the slab is around 20 degrees prior to fitting.

In normal running with a hot water heat pump, the slab will not experience hot spots or localised overheating, in fact the sun can get the floor hotter than a heat pump. When there is significant solar gain, the underfloor piping can act as an energy transfer system.

The golden rule using carpet for underfloor heating is to ensure that thick underlay (11mm or thicker) is not fitted. Take advice from your flooring supplier, they should suggest either a thinner underlay (7mm) or possible specialised products that are imported for this purpose.

We have found where living areas have hard flooring, with carpets in bedrooms, that the blanketing effect of the carpet reduces the relative temperature without adjustments being made to the flow rates on the manifold.

You can find following references online from a couple of UK flooring companies: 

Please always consult your specific flooring product with the flooring supplier.

About Cork...

Here is some info from a reader on Houzz named “atelier”
Read from the orginal website

“Anyway, I’ve installed cork floors over radiant heat both as floating and tile several times with no problems.

It is a common installation- you just need to follow certain steps to assure a good install. In brief: proper acclimation of the material, having the heat on “medium” (max surface temp. of 85F) 5 days before and during installation, a vapour barrier under the floor, and adequate expansion space at the perimeter, doorways, etc..
Definitely get an installer who has experience laying over radiant heat floors! 

As for your question about the insulation value of cork blocking the heat from a radiant heating system. I get this question often, and the answer briefly is that cork is entirely compatible with a radiant heat floor. Here is the answer and rationale in detail, explained in point form: 

1. A radiant heating system is not a quick-response system- i.e. it relies on thermal mass and heat radiation. That’s part of its efficiency and why it is comfortable- the floor constantly radiates warmth upwards. 

2. The insulative value of a material refers to how well it slows down the transmission of heat. The heat doesn’t dissappear or get absorbed by the material- it just takes longer the flow through. So in practice, floor coverings do not affect the overall operation of a radiant heat floor because the heat will eventually get through. Remember- a radiant heat floor is not a quick response system- you don’t just walk into a room and crank up the thermostat. (Of course don’t do something silly like install a radiant floor over a drafty, cold basement, because you’d lose all the heat out the basement first) 

3. Yes the insulation value per inch of cork is higher than that of wood but a cork tile is only 3/16″ thick. I did the math a long time ago and the total R value of 3/16″ of cork is almost exactly the same as 3/4″ of a typical wood. So putting down cork tile is no worse than putting down 3/4″ of wood. 

4. That being said, a floating cork floor will have a bigger R value than a cork tile floor, because it is on a 5/16″ mdf core, and thus will slow the heat transmission a bit more. I don’t tend to use a floating floor, unless specified or the price differential is less than the added bit of surface preparation to bring a floor up to cork tile standards. 

5. Finally, a site-finished cork tile floor will not gap visibly due to expansion/contraction of the radiant heat floor. Cork is a truly resillient material with excellent rebounding properties (95% recovery after 50% compression!) After all, cork itself is commonly used for control joints and gaskets. 

Lengthy answer, but I’m hoping if the issue comes up again, we can just link to this post. 

I hope I covered everything- If I’ve missed something, I’d be glad to follow up.”

Please alway consult your spefic flooring product with the flooring supplier.