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Radiant heat retrofit

I,m working on a circa 1818 building that has plywood over the original floors. If I put the tubing under the floor will I have to remove the plywood? Or could I route out the plywood and install it in the groves? I plan to put tile over the floor in some areas and no pad carpet over others.

Re: Radiant heat retrofit

No, there's no need to remove the plywood---in fact, you WANT to have as much wood bulk in the floor as possible.

The way radiant heat works is that the radiant plastic PEX piping transfers all the heat energy from the hot water into the wood floor structure---the floor becomes a giant radiator that absorbs all this heat & radiates it into the living space--the more wood, the more heat that can be stored to heat the living space---this is usually done by hot water (hydronic) radiant heat, but there is electric radiant as well.

This radiant method is known as under-floor radiant heat or sub-floor radiant heat---this assumes you have access the the underside of the floor (from the cellar or crawl space) so that you can staple up the PEX tubing on the underside of the sub floor.

Another radiant floor method, mentioned in your post, is supported by some companies that sell plywood floor panels that have PEX & reflector strips grooved into the plywood floor sections.

Tile is excellent for a radiant floor covering---carpeting has to be limited to non-plush, thin types, or else it will act as an insulator to the radiant floor heat.

Google "radiant floor heat" to get numerous internet sites that describe these radiant methods.


Re: Radiant heat retrofit

Thank you,
I understand the value of a heating mass, but I thought that wood was an insulator. So the more wood that the radiant heat would have to go through the less effective. That's why I was considering routing the grooves on top of the plywood. This way the two layers of wood would be a heating mass and also keep the heat going up.

Re: Radiant heat retrofit

I know, it's very hard to understand---but to speak of radiant heat one has to imagine 1) the buildup of heat energy in a mass such as stone or wood and 2) the invisible infrared radiant waves that eminate from the heated mass to the colder area---this is a quite different process than heating a room, say, with forced hot air, which by CONVECTION heats & circulates the warmed air around the room.

With infrared radiant wave heat it's like a hot object, like the sun, giving off invisible infrared waves of heat that heat objects on the surface of the earth only when they come into contact with them---radiant floor heat operates in this same way.


Re: Radiant heat retrofit

I guess this is why I am confussed. http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=99
Hanging in Joist Space
Tubing is suspended several inches beneath the subfloor in the joist space. Insulation is installed in the joist space beneath the tube with a 2 to 4 inch air space between the top of the insulation and the bottom of the subfloor. The air within this space is heated by the tube which, in turn, heats the underside of the subfloor.
Source temperature required: +++
Engineered Subfloor
An engineered, load bearing board takes the place of the structural subfloor. It has a laminated layer of aluminum and a channel to accept tubing. Hardwood floors can be nailed directly to the subfloor plates or carpet and pad placed over the plates. It is also possible to nail a second subfloor over the plates for a smoother finish for vinyl areas. A cement board is used when tile or stone is to be installed.
Source temperature required: +

My question is: Couldn't I create an engineered subfloor using the existing plywood, create custom routes, insert the aluminium
panels then the tubing? I could then cover it with what ever I needed,carpet,tile,wood.
Thank you for taking the time to answer my question.

Re: Radiant heat retrofit

What you describe is widely done with manufactured engineered sub-floor panels with laminated aluminum below the tubing inserts.

Such panels known as "Warmboard" & Wirsbo/Uponor's "Quik Trak" are some examples---they can be quite expensive but I have my doubts that a diy panel is a good alternative.

By all means seek out forums that specialize in radiant floor heat so you can have a "back and forth" discussion with installers who have a wide experience in these "engineered sub-floor systems"---I have limited knowledge in this area.

Also Google "radiant forum" subfloor for additional forums.

"The Wall" is a radiant forum at the heating help site, as well as ones listed below.

Also Google the "radiant panal association" for their forum.


Re: Radiant heat retrofit

Part of my house is heated with radiant floor heat, (additions). We love the comfort. We would like to heat the original part of the house with radiant, (hydronic). I did not realize that floor thickness could be an advantage...that was actually holding me back in finishing the whole house.

However, is it true that if I install radiant in the old part, (which has a crawlspace area), I will need additional insulation because of the floor thickness...(at least 2" thick wood).

I am also concerned with pests such as mice in the insulation. Is there an insulation that might provide more resistance to mice, etc and still provide good r-value?

Re: Radiant heat retrofit


I've had good luck "tightening up" crawlspaces with the expanding foam product---sold at the home improvement stores, but also in a large cannister at siding & insulation outfits---great for stopping mice & other undesireables.

As to putting radiant in the rest of the house---a lot would depend on 1) if the installers have full access to the floor underside thru the crawlspace; 2) that the heat output of your boiler is enough to heat everything when completely hooked up; 3) the severity of winters in your locale; 4) how much it will cost to revamp the present tubing & valve arrangements into a single system---it could get real expensive---they may want you to put in a new boiler.

The best thing to do would be to consult the Yellow Pages under "Heating Contractors" & get several quotes---if you are satisfied with the work of the installer that did the previous work, by all means, call them back.

Try to find an installer who has extensive experience in installing radiant---this type of work is a lot harder to get right the first time than other forms of heating.

Re: Radiant heat retrofit

what type of insulation do you recommend for the underside of the pex tubing?...(between the floor joists which are 8" joists).

Re: Radiant heat retrofit

I don't see anything wrong with staple-up pink insulation rolls with the reflective covering---keep the option of accessing the tubing runs in the event of future minor adjustments.

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