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Old 02-14-2008, 04:28 PM   #1
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Underground Hot Water Line


Can anyone give me some ideas as to how far I can run a hot water line underground with minimal loss of heat? Assuming the line is well insulated and buried at around 5 feet, and the source temperature is 145 degrees, I am hoping to run this line for 400-500 feet with a maximum heat loss of 15 degrees or so. I would like to provide heat to a number of outbuildings from a central heating source and am trying to find out if this is feasible. Thanks in advance for any info.

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Old 02-14-2008, 04:39 PM   #2
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Is this for in-floor heating?

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Old 02-14-2008, 05:01 PM   #3
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Underground Hot Water Line


You did not say where you are, so an accurate answer is impossible.

In many areas, you are proposing running a line of unknown diameter through 35 to 60 degree soil during the heating season. If it is a small diameter, the water will be about 50 degrees in a northern climate.

You probably need professional help and very good insulation to avoid losing your energy, especially in a cold climate.

Last edited by concretemasonry; 02-14-2008 at 05:12 PM.
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Old 02-14-2008, 05:23 PM   #4
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Underground Hot Water Line


Outside temperature is going to play a big part. You would need to install a re-circulating line to avoid waiting five mintues or so for hot water. That will also help you get warmer water during winter months. You would have to insulate them very well. Standard pipe insulation won't cut it.

Do these outbuildings have power? If they do just put water heaters out there. If they don't have power I would bring power to them instead of water lines. Not only does it solve the hot water issue, you now have power in the building as well which would probably come in handy.
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Old 02-14-2008, 05:41 PM   #5
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I am in Colorado. Estimated soil temperature at that depth is a constant 50-55 degrees. The pipes will be as insulated as it is possible (and economical) to insulate pipes. I might buy preinsulated pipe. I would guess the diameter would be around 1". I am intending to use baseboard hotwater heat and/or infloor radiant heat. I have excess heat from a geoexchange system so it seems to make more sense to use that rather than heat the buildings with electricity.
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Old 02-14-2008, 05:58 PM   #6
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It sounds like you may put too much load on the current system and take away from heating the main building. You'll have to do heat load calculations on the outbuildings and compare that the the output of the heat pump and go from there.
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Old 02-14-2008, 06:04 PM   #7
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That is a pretty big project. Thinking about it I believe you really need to consult an engineer or someone who can do the math to figure out if your system can handle it. Also just running that system may well cost as much as twenty years of heating the building with electric.
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Old 02-14-2008, 07:10 PM   #8
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Actually I think it's going to work out costwise. It would cost about $1000/year at today's electric rates to heat these buldings with electricity, and that is just the operating costs. I already have the excess heat so the operating costs of my system would be significantly cheaper, and I can do the trenching with my own equipment. So I will basically have the cost of the pipe, valves, pump(s), and radiators or whatever the heating mechanism is. Yes the system will have to be engineered, but I'm not at the stage of paying an engineer to do that. I was just wondering if anyone has had experience running underground hot water and if so, what distances/temperature losses were involved.
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Old 02-15-2008, 03:46 PM   #9
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ST,.....
Wander over Here,..... This is the kinda thing they do,.. All the Time....

I think your plan will work,.... I'm alittle Too New at it myself to help ya.....

I'm setting up an Outdoor Wood Boiler to do the same thing....
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Old 02-15-2008, 05:50 PM   #10
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Thanks Bondo, that forum has exactly the type of info I am looking for. ST
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Old 02-15-2008, 06:33 PM   #11
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Ayuh,..... See ya over there......
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Old 02-16-2008, 06:14 PM   #12
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Recently we had a customer ask us to spray 2 lb.(rigid) foam on his 1 inch pex lines running from his outdoor wood furnace to his house(radiant heat) here in the mountains of Virginia. They were in a ditch about two feet deep, 75 feet long, supported about six inches from the bottom. The foam guy just walked along shooting the bottom of the ditch with about 10-12 inches of foam which completely encased the pex. The customer is very satisfied.
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Old 03-08-2008, 10:14 PM   #13
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Originally Posted by scrapiron View Post
Recently we had a customer ask us to spray 2 lb.(rigid) foam on his 1 inch pex lines running from his outdoor wood furnace to his house(radiant heat) here in the mountains of Virginia. They were in a ditch about two feet deep, 75 feet long, supported about six inches from the bottom. The foam guy just walked along shooting the bottom of the ditch with about 10-12 inches of foam which completely encased the pex. The customer is very satisfied.
5 years from now he wont be..that foam absorbs moisture..i have seen that stuff dug up and a man could not lift a section 12 feet long... and when that happens there is no insulation value left in it.....you will see the ground is thawed over the pipe
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Old 03-08-2008, 10:20 PM   #14
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Originally Posted by st940692 View Post
Actually I think it's going to work out costwise. It would cost about $1000/year at today's electric rates to heat these buldings with electricity, and that is just the operating costs. I already have the excess heat so the operating costs of my system would be significantly cheaper, and I can do the trenching with my own equipment. So I will basically have the cost of the pipe, valves, pump(s), and radiators or whatever the heating mechanism is. Yes the system will have to be engineered, but I'm not at the stage of paying an engineer to do that. I was just wondering if anyone has had experience running underground hot water and if so, what distances/temperature losses were involved.

i run my water about 250 feet in older type inuslated 1 inch pipe..todays new insulations keep heat loss much less i believe...i lose 7 degrees in a round trip (from the furnace to the house and back)..l when the house is not calling for heat, just circulating Like i said , i am sure with the better insulation you can do better
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Old 03-09-2008, 08:37 AM   #15
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Originally Posted by billie_t View Post
i run my water about 250 feet in older type inuslated 1 inch pipe..todays new insulations keep heat loss much less i believe...i lose 7 degrees in a round trip (from the furnace to the house and back)..l when the house is not calling for heat, just circulating Like i said , i am sure with the better insulation you can do better
I believe the heat loss characteristics of the old asbestos insulation is actually better than that of the newer foam.

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