in floor heat


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Old 11-14-07, 07:59 PM
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in floor heat

i am new to this site so excuse me if this has been asked already,first of all we live in a modular home with a full basement and we heat our home with hot water which we get from our outdoor wood boiler and my question is about the in floor heat is it possible to attach the tubing directly to the bottom of the subfloor i know these systems are usually in the floor i did also have one person tell me that it would not be very effective having it attached to the bottom of the subfloor because it is not covered but the last time i checked heat rises so either way it should heat the floor correct?
 
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Old 11-15-07, 05:13 AM
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Yes. They make it so you can attach it between the floor joist. I was considering this option for a small bathroom but the guy I was working with suggested going with electric do to the size of the room and how well it will be insulated.

If you are really interested in radiant floor heat check out this site. The guy that helped me was Rob, I sent him a boiler legend and he drew up plans with the required parts and pricing and a plumbing schematic. There are other sites on the net with info and free estimates but I felt this guy was knowledgeable and took the time to answer all my questions.

http://www.nrtradiant.com/
 
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Old 11-15-07, 03:51 PM
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now if i was to do something like this does the water temperature need to be regulated for the tubing under the floor i was told that it does but if i understand this right you should only have to regulate it if say you were heating up a concrete slab because that needs to be done gradually correct?right now the water coming in to our home is coming in between 178-190 degrees so would that be fine to have it at that same temperature for heating the floor?
 
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Old 11-15-07, 04:14 PM
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First thing to remember is that heat travels in all directions towards a colder area. If you do not insulate under the heat tubing you WILL end up heating the basement.

Second thing to remember is that you do not want your finished floor to be more than about 80 to 85 degrees maximum. To accomplish this you must regulate the temperature in your floor heating system.

Third thing is that anything more than about 140 degrees in your floor heating tubing will probably be way too hot.

Radiant floors are best when they are made of a heat sink material (like lightweight concrete) and are adequately insulated on the non-heat-desired side but there are many retrofits that have the tubing attached under the subfloor. It is best when such installations utilize aluminum pans that hold the tubing and conduct the heat to the subfloor.

If you are considering on replacing your finish floor you may be better off by using something like warmboard to place the heating tubing directly beneath the finish floor.

There are a lot of other considerations that need to be taken into account.
 
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Old 11-15-07, 04:19 PM
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You should really study as much as you can about radiant heating before you make any decisions. It's a lot more complicated than it seems at first look!

You said "Heat rises" ... not exactly...

Heated AIR rises.

HEAT always goes from warmer to cooler areas/objects, regardless of the direction. Up/Down/Sideways... whatever, wherever... they are RAYS.

If you do use radiant on the bottom of the floor, you must use PLATES over the tubes to spread the heat out. You also MUST (absolutely) install a RADIANT BARRIER _under_ the tubing. This barrier is necessary to reflect the radiant heat that is travelling downward. Below the radiant barrier, you MUST install insulation.

The water temperature for floor heating should probably never be above say 100*F or so. A floor that's heated above say 85*F can be very uncomfortable. It might be nice for a little while on cold footsies, but after a bit, you will be evacuating to cool your feet. Some finish floor surfaces can be damaged by excess heat also, so choose your finished floor carefully.

There are methods of under floor heating that use higher boiler temp water, basically the tubing is stapled to the sides of the floor joists with an air gap between them and the bottom of the floor. You still MUST install a radiant barrier and adequate insulation.

To lower the water temp you will need to have a mixing valve and a temp controller installed on the boiler piping that feeds your radiant tubing.

What seems simple at first usually isn't !
 
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Old 11-15-07, 04:38 PM
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thanks for all the info and i want to make it clear that this is all new to me and iam basically learning as i go which i am sure you have figured out already but anyway i dont know if i metioned this but our home is already finished and i will not be re-finising the floor i just was not aware that you could attach the tubing right directly to the bottom of the subfloor and as far as what we have now for flooring basically half the house is carpet and half is lonoleum (sp)? also is there a certain kind of insulation that you use to insulate the underside of the tubing?
 
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Old 11-15-07, 05:14 PM
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Like the others have said, you don't want to attach bare tubing to your subfloor. It doesn't work. You need transfer plates. You don't want more than about 140F water or the floor will get too hot. When carpet gets too hot, it starts to de-gas all kinds of nasty stuff. So does vinyl, I believe. Linoleum probably cracks.

Carpet also hugely reduces the performance of radiant floor. It basically insulates against heat transfer.

Getting radiant right is not hard, but it requires a LOT of homework. Check out that nrt site. They are good.

Getting radiant wrong is easy, unpleasant, and very expensive.
 
 

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