Heating Under Suspended Wooden Floors

Radiant heat under wood floors works fine if done correctly. Suggest researching several sites like the following to gather more information before your decide.

http://www.woodfloorsonline.com/techtalk/woodwater7.html

did it in my house, but instead of rock wool, I used styrofoam sheets with a reflective face

Thanks Guest. Did you put in piping or ducting? If so, from underneath? dbokkie

As far as I can see, you will find that the wood is a good insulator, so the rate of heat transfer will be low. That means with a heat source of 30-35C it will be fine for steady state, but if you open the door and cool the house, it will take a while to recover.

The lower insulation, foam with metal IR reflection is fine, and the difference in the R value of the upper wood and lower foam will determine the effectiveness.

Say you use R8 foam and the 1" wood is R1, then 1/8th of the heat will heat the basement.(more or less).

Now, the key is thinner wood, as long as you have good support.

lots of stuff here

http://www.google.ca/#hl=en&safe=off&q=%22sub-floor+heating%22+%2Bwood&meta=&aq=f&aqi=&aql=&oq=%22sub-floor+heating%22+%2Bwood&gs_rfai=&fp=2911983a5b1aa07d

Hmm. Interesting, but a bigger job than I was anticipating, but would be a better long term outcome, maybe. I was hoping to use the existing floor level and add the goodies beneath it which would involve accurate levelling of pipework. dbokkie

You must realize that will increase the drying effect of the wood during the heating season. Coupled with the damp summer months, it will quickly produce large split between the boards of real wood. Special attention to room humidity will have to be given all year round.

Of course, this does not apply to most engineered (plastic/resin/fibers) wood products. It simply increases the amount of glue solvent released and might increases brittleness.

In my (not always so) humble natural wood lover opinion, floor heating is best used with with ceramic covering.

But some people have used it in recent years. I am yet to see the results after a few years.

The floor heating method is great because it uses a big surface area to radiate the heat and therefore the media temperature remains very low compared to other heating methods...

The floor temperature should not exceed 27 deg C and is best kept at 22 to 24 degC most of the time.

With these temperature and some advice on the type of wood and treatment (not so difficult since available in the market for specifically floor heating...Web search Floor heating ...), you should not have any problems. keep the humidity at at least 60% RH = good for floor and people.

60% RH cannot be sustained all year round in cold climates. This will give condensation problems on or in the exterior walls insulation followed by mold. Up here in Canada, I have to go to 40% in winter. I actually try to dehumidify in the summer to prevent the humidity to go above 50%.

Home owner who don't do any humidity control will see about 15% RH in the middle of the winter and up to 80% RH in August. This is very hard on natural wood as large spaces develop between the planks over the years.

Thanks for the detail regarding temperatures. dbokkie

I have been looking into it for a house near the Jersey Shore that has a crawl space. Most of the radiant heat websites warn against using real wood floors and advise using the laminates or engineered wood floors. I'm also planning on using the reflective faced foam on the underside due to the moisture under the house in that area. If fiberglass or rock wool ever got wet it would act like a sponge and possibly mold or mildew could form.

I believe that the lack of good heat transfer through a thicker wood floor plus the drying out of the wood are probably why they don't recommend real wood floors.

Thanks. The foil based foam tends to be far more expensive in the UK, but I had the same reservations about mould in the rockwool, although this was pooh-poohed by my architect friend.

I personally intensely dislike underfloor heating for a very simple reason, it cannot follow the outside temperatures quickly enough. Especially at this time of year and in the autumn, it can be cold overnight and the mornings (today in Germany for example) and warm midday and/or afternoons.....

I have never seen an underfloor heating that could handle that quickly and properly....you were either too hot or too cold.....

If someone is ill and you want to warm their bedroom up quickly, you will need to keep electric fires handy as the wait of between 12 and 48 hours (depending upon type of floor, is simply far too long!!

With wood, I envision big gaps/splits appearing eventually, plus very restricted heat flow....

May I suggest that you try it in a small area first, one room for example.....

May i suggest having both rads and the floor together, turn off the one thats not needed at the time......now that could work.....especially in the bathroom..

I was intending to keep the rads as you suggest.

It was an architect who suggested the use of rockwool as I had suggested the use of foam due to the presence of high humidity in the underfloor spaces, which I envisioned would be trapped as moisture in the rockwool. He said it would be without problem.

I also would only put heating in the areas where no furniture was likely to be placed.

I originally was considering liquid transfer of heat as used in ground source heat pump application but having seen how critical the pipe laying has to be both in the ground and under the floor, I feel that the future problems with air locks would be probable and unacceptable. As the temperatures are low would warm air ducting be sensible?

Heating speed: When floor heating and in properly insulated homes, you can keep the heating on all the time with a thermostat setting at 20degC to 24 degC depending on the time of day and occupancy. That iswhy you will need a programmer controller as in normall heating.

Keeping the internal temperature of the house constant without too much fluctuation is beneficial for the house and its furnitures etc... This is achieved cheaper when using floor heating because the water temperature will not exceed 40degC in the heating coils. (consult some specialised sites...)

Floor material: Definitely, the type of floor is important to avoid deterioration: Parquet floor or treated wood are best if floor is to be wood. Any other material can be checked for suitability. Cracks and damages are normally due to the excessive temperature rise in the heating fluid when not properly controlled to be <= 40 deg C. Some safeties are normally required to prevent accidental excursion of the fluid temperature above 40degC.

http://www.greenbuildingtalk.com/Forums/tabid/53/aff/12/afv/topics/Default.aspx

or www.radiantpanelassociation.org

These are good sites with experts in the subject answering your questions. Putting heat tubing in the joists as you suggest is one of the least effective methods from an efficiency viewpoint, but still can be wonderful comfort heat.

First order of business is to do a heat flow analysis and be sure to survey the R values of the insulation in your sidewalls and ceiling as well as your windows. Get a competent radiant designer to put this information into one of the many radiant programs that are available. This will tell you how much flow you need at what temperature. They will likely tell you to use heavy gauge aluminum heat spreader plates that fasten to the subloor and insulate and seal the heck out of the area below. The warnings about wood are true the hotter you get the floor. If the building is well insulated otherwise the lower your radiant temperature needs to be and the easier on the wood. A lot of radiant is used with concrete floors for the thermal mass effect. This takes a long time to heat up, but radiates for a long time and takes a long time to cool down. Wood floors should heat up and cool down more quickly. A device called an outdoor reset will sense a trend in temperature and turn on or turn off your system rather than relying on your room thermostat to prevent the effect of a warm floor on a warm day.

Good luck!

Thanks. I had not considered the heat spreader plate. I guess in the underfloor joist situation this would be above the pipes. This has given me an idea. I could pre-fab lengths of Al with clips for the pipes underneath to ensure level layout. However this would not seal the floor/insulation from any damp below.

http://www.radiantec.com/pricing/individual-prices.php

Scroll down to radiant heat emmision plates. Surely somone makes these in UK.

Additionally, there needs to be about 2 inches of air gap between the reflective surface of the insulation below the heat plates and the sub floor. The Radiant Panel Association in the US recommends the insulation have an R5 over heated crawl space or R13 over unheated space. Be sure to seal this area in so that the trapped heat is captured.

Regarding dampness, we normally see 6 mil or thicker polyethylene film put down directly on the ground surface in the crawl space. Having said this, it is imperative to have the area ventilated.