Radiant heat under wood flooring

chitowntommy

I am currently considering radiant heating under wood flooring I will install. I currently have radiators where the radiant heating system will go. The room is 14'x16' with 8' ceilings. I am considering the staple up system in the joist bays. I have learned that it is necessary to keep the water temp of the loop below 115-120* and to achieve this I would need to add a mixing valve between the supply and returrn for the loop. I have seen that PEX is a common material used for this application and read that 5/8" diameter tubing offers a good mix of cost, ease in installing, and flow.



Additionally, I have learned that EPDM is a material is very flexible and easy to work with. That said, it is substantially more expensive and I read that it does not work well with Cast Iron boilers (mine) because it allows for rust buildup, and it also allows/promotes the growth of algae.



1. Could I get some input on the use of PEX and the deal with EPDM, that is, does it have the problems with rust build up and algae?



2. With the mixing valve, do these valves have their own thermostat, or is it necessary to have additional components?



Any additional thoughts or comments will be appreciated.



Tommy

Simply Rad

???????

Just curious as to where you learned all this information.

Jeffrey

chitowntommy

Re: ????????/

Reading a lot on the net and talking with the guy at the supply house.  I don't know how much is accurate and that is precisely why I am here.



Thanks,



Tommy

Simply Rad

Reason I ask is there are alot of variables in your questions

First and foremost calculate your heatloss for the space you are heating. Every room requires a different amount of heat. Therefore saying that you want to keep the supply temps below 120f is not accurate, because you may not be able to heat the home. The heatloss will dictate the loads and supply temperatures. Especially if, you are going to use the staple up method. I will NOT install the staple up system, unless we use aluminum heat transfer. Where I live it is unable to do the job and I believe its a cheap imitation to a comfort system.



Radiant is a comfort system not just a heating system. I would not use a standard manual mixing valve to set the temperature. By doing that you are setting the system for the coldest day and the rest of the time its too hot, there for creating a roller coaster ride in room temperatures. Use a mixing system with an outdoor reset control, its adds comfort and efficiency.



Rubber hose....have you ever changed the radiator hoses in your car or belts. Well thats rubber for you. How is the customer going to change the rubber hose under their floors? I would use PEX And if you are go to use the staple up method yo do not want to use 5/8 tubing. Thats a big hose and you will fight it the whole way. That why they make 3/8" and 1/2" tubing. With 5/8" tubing you are able to run longer loop lenghts with less flow restriction. Keep your 3/8" loops less than 200' and your 1/2" less than 250' and things work great.



Jeffrey

chitowntommy

RE:

Thanks for the info.  I have done some more research and see that 3/8" is much easier to deal with.  I plan to use the transfer plates, in addition to foil backed insulation. 

As for a heat loss calc, you are right.  I need to get on that.  The room will be a almost complete gut job, so I plan on insulating properly. 



I mentioned the temp limitation in that I understand it that having too hot of water in contact with the subfloor can cause problems with the wood floor above.  I agree that if the heat loss is too great, the 115* temp limit might be insufficient to provide proper confort. 

Thoughts on heat calc options?

Thanks,

Tommy

chitowntommy

RE:

Well I did a heat calc and got about 9500 BTUs/Hr.

I am wondering if this sounds in line with the following.

Room Size is 14x16x 8' tall.  The ceiling will be covered with 5/8" DW and I should be able to achieve about a 20 R value from insulation, but I have to see the space up there to be sure.

The walls are brick with studs and will be covered with insulation and 5/8" DW.  The walls have windows on 3 of the 4 sides that have a total areal of 135', and they are older wood with storms.

The floor is over an unheated garage and I believe the joists are 2x12s so I expect to be able to achieve around R-30 of insulation there.  I plan on using 3/4 ply subflooring and 3/4 finished hardwood for the flooring.

Does my calc sound within the ball park?

Thanks,

Tommy

CMadatMe

Heat Loss is High

You must use a radiant design heat loss. You cannot use a conventional heat loss. The load on a room of that size should be around 6,000 btus.