Pex under joists outdoors?

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Old 11-20-19, 10:19 AM
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Pex under joists outdoors?

I'd like to run under floor radiant panels between the joists under my sun room. They are 2x10 and would have r30 insulation, covered with 1/2 plywood. Would this be enough to keep the pex from freezing?

Thanks.
 
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Old 11-20-19, 10:41 AM
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Is the pex providing hot water to the panels? What temp zone are you in?
 
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Old 11-20-19, 01:01 PM
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Anything can freeze without heat regardless of the amount of insulation. Insulation only slows down how long it takes.
 
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Old 11-21-19, 06:34 PM
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I'm in MA, how can I make my location show... It used to. I know insulation doesn't magically create heat, but I'm just asking if this is put into practice. I suppose at least a few hours a day this would running in freezing temps. And yes these would be in those panels screwed to the bottom of the floor.
 
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Old 11-22-19, 05:34 AM
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"...just asking if this is put into practice." Asking if what is put into practice???

Whether or not the pipes freeze depends totally on how well the room and floor is insulated, how cold the weather is and how much the heat is run to warm the water. Having the heat on for only a couple hours means it could go 20 or more hours without heat. In which case it's possible the pipes could freeze. In your case a heating systems that uses glycol to prevent freezing might be a good idea.
 
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Old 11-22-19, 02:28 PM
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Well, you know you can say that pipes in an exterior wall of a 2x4 house won't freeze (I've been in many houses that have this)? I'm just looking for an answer like that.
 
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Old 11-22-19, 02:45 PM
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You just said "...pipes in an exterior wall of a 2x4 house won't freeze..." then said "...I've been in many houses that have this.". You want us to say something then say the opposite???

If you do not have that zone on it has the potential to freeze. The amount of insulation doesn't matter. Insulation will buy you time but eventually the cold will win on a really cold day. During the shoulder seasons good insulation might be enough to get you through 20 hours with the zone off but during the coldest days it might not and you could have frozen pipes. You either need to run a fluid that won't freeze or run the zone at a low level to prevent it from freezing.
 
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Old 11-22-19, 08:15 PM
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Haha no. I was just looking for someone to say "yes I do that all the time" or "no i did that once and everything froze".
 
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Old 11-23-19, 05:54 AM
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Hi, just curious as to what the floor surface above these panels is, and how well it would conduct heat.
Geo
 
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Old 11-23-19, 06:15 AM
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Ok, for what it is worth, I did it and it worked. Had a home in the Colorado mountains with a room elevated on piers about five feet above ground. Pex pipes to hot water baseboards and to bathroom ran in joist bays of floor. Added ten inches of fiberglass insulation, then 6 mil plastic, then three inches of rigid on the bottom of the joists. Had glycol in the hot water heater system for the first two years. Then drained it and ran just water after that. Obviously nothing in the water supply to the bathroom.

Had zero problems over ten years. Usually had about twenty nights per year when it was zero degrees Fahrenheit or below. For the first few years the baseboard heat ran to heat the rooms. Had a few power outages, but never for more than maybe 15 hours at a time when it was that cold. Where we lived it could get that cold at night, but always warmed to at least 15 degrees during the dats. I know if it was below zero for days might not have been okay. But I did heat the rooms with a gas style wood stove for several entire winters and never used the baseboards even during those super cold spells.
 
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