Underfloor hydronic in the Northeast?


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Old 10-28-09, 10:49 AM
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Underfloor hydronic in the Northeast?

Hi,

My wife and I are in the process of buying a modular home in New Hampshire and we would like to use radiant floor as our main source of heating. We have heard however that underfloor radiant heating isn’t working too well with our Northeastern winters. Apparently, the system is unlikely to be warm enough to heat the house comfortably unless we install the pex over the floor with "warmboards" for example?

The floor is made of ¾ inches OSB sheating and we would use aluminum transfer plate to attach the pex tubing under the floor. We would also use one layer of ¼ inch cement HardieBacker® Board before tiling the floor. Will this system work with water heated at 120 degrees for example?

All advices and suggestions are welcome! Thanks in advance!

Jean-Francois
 
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Old 10-28-09, 12:03 PM
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Hi Jean-Francois, and welcome to the board. I just recently audited a top of the line home, modest 1,800 sq ft ranch, but they have the bucks, retired and enjoying life. I say modest because the well-to-do homes around me are all 3,000 and up. To the point, they have 7 zones of radiant heat, installed under the sub-floor, installed from the basement and under hardwood floors. In other words it isn't buried in cement. Some tile in baths and kitchen. Set it and forget it, no programming it to go up and down, too slow. However, this house is insulated and sealed so well, one of the best I have seen. @' rigid foam around the entire basement. All good windows. 6" walls with fiberglass and rigid foam. A system 2000 boiler. Should be no problems, except they are using twice the oil they should be, 900 gallons. My work was in and out, so I don't know if he took any action, although the recommendations were minor. My thinking was the radiant heat was heating the basement more than it should have, but even that did not justify the quantity.

Installed properly and isolated to the area you want to heat, it should be fine. I think one of the issues you mention is the subjective difference between a room that is 70 degrees and that is it, vs a room with a 180 degree radiator or fireplace to snuggle up to. Having lived with wood heat, I enjoy the warm spots when it is cold.

Ther are other issues that are being noticed as we insulate more homes to the max, and that is the heating systems are smaller and run less often. The subjective effects of this are being noticed, but the solution, or preference is not obvious.

Enjoy your new home,
Bud
 
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Old 10-28-09, 02:02 PM
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Originally Posted by JFCarbonneau View Post
Hi,

My wife and I are in the process of buying a modular home in New Hampshire and we would like to use radiant floor as our main source of heating. We have heard however that underfloor radiant heating isn’t working too well with our Northeastern winters. Apparently, the system is unlikely to be warm enough to heat the house comfortably unless we install the pex over the floor with "warmboards" for example?

The floor is made of ¾ inches OSB sheating and we would use aluminum transfer plate to attach the pex tubing under the floor. We would also use one layer of ¼ inch cement HardieBacker® Board before tiling the floor. Will this system work with water heated at 120 degrees for example?

All advices and suggestions are welcome! Thanks in advance!

Jean-Francois
Thank you Bud,

Do you think possible that the excessive oil used is caused by the fact that the tubing is under floor?

Thanks again,

JF
 
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Old 10-28-09, 04:44 PM
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Where the tubing is located is more of an issue with the speed of the delivery. As long as the heat can't go where you don't want it to, it will eventually soak up through the floors. But if you come home, chilled to the bone, and want a quick shot of extra heat it's not going to be there. An air tight gas fireplace could fill the gap and act as a backup heat source when NH looses power. Radiant floor heat is not bad, just slow and steady. I know the first place my wife runs, actually the second place, but she has to crank up that thermostat as soon as she gets home. A radiant heating system cannot do that. Recovering from a setback of 5 degrees could be several hours.

I'm not an HVAC guy, but I believe it is not difficult to mix radiant heat with some baseboard or even a cabinet heater. They make a good place to dry out the socks and mittens.

Bud
 
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Old 10-28-09, 05:34 PM
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In general, and this holds true with ANY heating system, in order to maintain a comfortable temperature, you have to be able to replace the heat lost with the heat input... basic, right?

The problem that radiant might have is with improper installations. There are limits to the number of BTU per square foot that can be input from a radiant floor. Let's just take a ballpark figure of 25 BTU/sq ft as an example. Now, say we've got a 10x10 room, 100 sq ft, it would follow that 2500 BTU is the most heat we can input. If the heat LOST from that room is more than 2500 BTU, it's gonna be cold! Elementary...

The very first thing you need to do is have an ACCURATE HEAT LOSS survey done. You need this on a ROOM BY ROOM basis. From there, you need a DESIGNER WHO UNDERSTANDS the realities of radiant heat, and can design a system that will meet the demands. If you hire just any old heating guy off the street... "Oh yeah, Oui Monsieur, I've installed LOTS of radiant" ... and he starts stapling up the tubing all willy-nilly without any thought to what he is really doing, well, it's gonna 5uck, plain and simple.

I guess what I'm saying is find a REAL radiant heat designer, and he will get it right, and you will be happy.

But now, that recovery thing that Bud is talking about, that's a real concern too!
 
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Old 10-28-09, 08:35 PM
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I would think some of those stories about radiant 'not working to well' are probably undersized designs using ie a water heater for source heat. As was stated, you need to do a proper heat loss at design temperature for your location, and make sure your heat source is properly sized (not grossly oversized tho !).

We have had in-floor (in-slab) radiant for 7 or 8 yrs now. I had started doing some research into gshp lately and had a fellow come out. He thought that I must be kidding for the oil we use annually on this structure.. I think its the in-floor letting us use less oil. I cant compare apples to apples though.

One thing I might note though.. and its not often discussed.. with purely in-floor (or rads), you have no air movement. Some people (ya, have talked with a few) find that portions of their house get stagnant. They use air fresheners etc. As it happened, ours is 2-story so we have in-slab on the main floor.. but forced air (air handler) for the upper floor. I also put returns only into the lower floor ceilings. This rotates the air around some as long as the upper floor is calling for heat.

Just something to keep in mind..

I love my in-floor, but Id never design a house without some air movement.
 
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Old 10-29-09, 02:26 PM
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Thank you Trooper and Dave, This is all very helpful discussion.

Best,

JF
 
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Old 10-29-09, 04:50 PM
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Avec plaisir, bonne chance!
 
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Old 10-30-09, 09:19 PM
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I'm in the northeast and have radiant heat that was placed against the floor (not in any concrete). It works great. There is truth to the slower rise time, but it is really a nice feeling to have the floor warm on a cold snowy day. I wouldn't switch to anything else even if I could. My oil use has gone down because we tend to keep the rooms about 5F cooler since it has been installed. I think it has something to do with the floor being warm and not needed the ambient air heated as much
 
 

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