Replies

1. 
   Guest_ | Oct 09, 1999 01:18am | #1

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   Anthony -

   You are going to need a mixing valve. You don't want to lower your boiler output temp to the temperature needed for radiant floor heat. Cracking the boiler is less of a concern than cracking your floor by over heating it. A simple mechanical valve is all you need, and they are about $75.

   There are many ways to do RFH and I know others here will chip in with other suggestions, so take whatever one you feel suits your circumstance. I have run tubing under tile, but I used a wet bed, and it has to be fairly thick. There are other ways but this is what I'm familiar with.

   One simple way to control the floor would be to plumb it so that it runs any time other zones in the house call for heat; then use the mixing valve to adjust the temperature of the input water to bring the floor where you want it.
   The colder it gets, the more often other zones run, the more often it gets heat.

   In my experience input water temperature should almost never be above 120 degrees, and the floor shouldn't be much above 90, or you risk cracking the floor. Also, if you use a wet bed, put strips of foam around the edge of the wetbed so it has room to expand and contract. Good luck.

1. 
   Guest_ | Oct 09, 1999 04:29am | #2

   *Anthony,I would agree with what Nick says on lowering the the floor temperature the new addition sees. I disagree somewhat with placing the priority of the "new" floor over that of the boiler. I think I know what Nick is suggesting but honestly I can't assume that you understand the ramifications and implications of upsetting the pre-existing system. Seems reasonable to me and I think Nick would probably agree given the chance to personally inspect your situation.Coupling the new addition on the same zone as the highest heat loss zone(zone most likely to be calling at design) is a good idea......EXCEPT at outdoor temperatures above design AND taking into consideration comfort, effect on boiler return temperature, etc..Many hot water baseboard designs were/and are still based/sized on a proportionate temperature drop from one section of BB to the next. Many times the heat load of an entire floor of multiple rooms with drastically differing heat losses were based upon the water temperature/output from the baseboard radiation from one room to the next. Series configuration in particular. In many cases, only the original designer/installer could confirm this without a site visit.Realistically Andrew, there is no substitute for an onsite evaluation of your existing system before you upset the balance by adding another heat emitting surface.Advice, even mine, on the internet is no substitute for engaging a true onsite look/see by one who understands your present equipment, piping configuration, analyzing the temperature drops, etc.To cut to the chase..........engage a local HW heat specialist to evaluate your system before making changes to something that has been balanced and properly working for years before making changes.We all mean well when we lend a helpful hand on this forumn but we could be wrong.........unless we are actually able to witness first-hand how your system is setup and operates. Even then, without proper knowledge AND experience we could be wrong. Caveat Emptor? You could always sue us for the wrong advice?Am I making any sense here?Jeff

1. 
   Guest_ | Oct 09, 1999 05:40am | #3

   *Jim - I totally agree with you about having a professional who has experience with heating look at the situation; every situation is totally different.I also agree about not tapping on to an existing zone of heat, disrupting the original configuration. To clarify, when I have done this in the past it has been piped as an independent zone that uses a relay to switch the pump or zone valve when other zones call for heat.Often changes to existing systems do have unforeseen effects. The aspect I like about having a small radiant zone linked to other zones and moderated with a mixing valve is that it helps eliminate potentially costly and complicated controls like outdoor resets.

1. 
   Guest_ | Oct 10, 1999 08:03am | #4

   *The Journal of Light Construction has an article on "Hardwood Flooring Over Radiant Heat" on their website:http://www.jlconline.com/jlc/archive/energy/radiant_sept99/index.html While it focuses on hardwood floors, the author comments at length about the proper temperatures of the heating fluid to obtain the best floor surface temperatures.

2. 
   Anthony_Rich | Oct 10, 1999 08:04am | #5

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   We would like to install a radiant heating system in our new bathroom. The room is stripped down to the 3/4 plywood which sits on 2x12s at 12 inches on center. I have a baseboard hot water system that is typical of the NY area. Since the bathroom is small, about 120 total sq. ft. and the area that needs to be heated is only 80 sq. ft. can I run some kind of tubing and not use a mixing device. I do have control over the temp. output of my boiler if this would pose a problem.. I can't see the water cooling enough, after running through such a short length of tubing, to crack the boiler. Please advise me before I make a mistake. PLease include advice on base, I usually use wire and thin set or Wonderboard under the tiles. The tiles in this case are 3/8 granite.