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Radiant Heat Questions
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Posted by mark_g (My Page) on Sat, Mar 7, 09 at 18:52
| I had a staple-under radiant floor system designed for our new house that's under construction in upstate NY, and feel I am in between the designer and the installer.
Feedback on the following questions would be appreciated:
1) Designer spec'd Pex B. Installer says "A is easier to work with", plus B kinks and has too much memory to make the loops (esp the extra loops that are like pigtails on the exterior side of each bay).
2) Designer spec'd runs to max out at 500', though many are shorter. Installer says that rather than have any run that long, break it into two 250' runs.
3) Designer spec'd no runs in the bay closest to the rim and wants that insulated only. Installer says tubing should be run through all bays to give most even heat. He is uncomfortable leaving out tubing in the outside-most bay.
4) Designer spec'd valves on the manifold. Installer says he usually uses separate zone valves, or something to that effect. He said that way is cheaper, not better.
5) I can buy the main parts of the system all plumbed and mounted to a backboard. The installer said we're not saving anything by doing that off-site.
These are the main differences. Unbiased feedback appreciated. Thank you, Mark
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Follow-Up Postings:
RE: Radiant Heat Questions
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| Still haven't got it through my thick head how that heat will generate through a wood floor, but that's just me...... Think I'd go with the installer because he's the one that has to stand behind his work. Dave |
RE: Radiant Heat Questions
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| Since this is new and in cold-land, have you insulated outside the foundation walls? We all know that cold comes from the outside, not from inside the house. So insulating and heating right at the source of the cold is the best means to create a sensation of warmth. Furthermore, ASHRAE has determined that human comfort is highest when the temperature spread is lowest between the coldest part of a room and its warmest part, and that the subjective sensation of cold is highest when ankle height temperature is low compared to head height temperature. In that case, you probably want to have the highest comfort without spending large marginal (additional) cost. I recommend putting the largest amount of heat (Pex) possible in the outside bay, and I'd put the Pex as close as allowable in the 24" nearest to the rim / perimeter / foundation. Then, you need less Pex in the rest of the floor, which is most of the floor. For some of the comments above I might side with the installer, if Ihad to choose between two without knowing the facts. I fear you might not have a qualified installer to make the big system-level decisions. Is he a plumber? A Master Plumber with insurance and licensing, who can train apprentice plumbers ? Or is he an installer? If so, you may have two people advising you who are not highly qualified. Post the most technical questions about products A and B (naming them) on
http://www.terrylove.com/forums/forumdisplay.php?f=6
http://www.terrylove.com/forums/index.php HTH
-david |
RE: Radiant Heat Questions
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1. Pex A & pex B refer to 2 ways of manufacturing pex. One manufacturer will pick A and the other will pick B. Aparently there are advantages and disadvantages to both. I would not worry about it. What brand and type does the installer want to use?
2. 500' is on the long side but ok. Splitting it up is fine. Technically the pumping requirements will change but most likely the pump selection will not change.
3. I have not heard of someone not using the 1st bay. The coldest area would be next to the exterior wall so I would want heat there. You are losing heated floor area also so that doesn't make sense. I'm not sure what would be gained by not heating the 1st bay.
4. This depends on how the house is zoned. If you have each room on its own zone than separate valves are not required. Typically you would have say, the living room and dining room on the same zone. The dining room might have 1 loop and the living room 1 loop. In this case having valves on at least the return of each loop is important. If the living room is warmer than the dining room you can partially close the living room loop to produce less heat and even out the temp.
5. Some contractors like to buy a preasembled panel but most do not. Typically your labor rate has to be fairly high for it to make financial sense. Also if the contractor has more work than he can handle he might buy it to save time. That is unlikely in this market. I would let him do the work on site. |
RE: Radiant Heat Questions
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Well, Hi Mark, lots of different opinions here !
I'm specialized in geothermal heat pump and radiant floor heating...
I work ONLY with PEX A (I like Wirsbo tubing) for more than one reason and one of them is the ease to bend it (3 inches radius) and if it would kink at any time, I can reform it simply by heating it with a hot air gun to regain original form, it's also very resistant to freezing.
So, 500 feet IS TOO LONG for 1/2 in pipe (this is the piping size to use under and over flooring), limit it to 250 feet if you want a comfortable floor (10-15 degre F delta T design).Spread them 8 to 12 inches apart depending if you're between joists or cement over poured.
I do my own pumping pannels so I can zone from the technical room (everything in one location)and I feed the collectors with 3/4 in tubing (PEX A again) it's a good way to cut costs for the customer and have a good zoning system.
As for the layout, always feed the outside walls first and finish with the center. Best of all, use one or multiple circuits (max 250 ft) per room and enter the room by the openings (to avoid nails in the tubing when putting up the divisions).
That being said, I think that your contractor knows what he's doing. I would trust him more than the designer... |
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