Outdoor Wood Furnace Info
All-Purpose OWF Discussions => Plumbing => Topic started by: heat550 on October 17, 2017, 12:34:06 AM
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If you had 100 ft of line in the ground and you were loosing 1 degree . 500x7.5x1=3750 BTUs (7.5 GPM) and your boiler was 50% efficient ( some are more ) . That's over a pound of 20% oak per hour
24 lbs of oak a day . 168 lbs a week 2688 lbs 16 weeks in a Minnesota winter just for the trench. can anyone prove my math wrong ?
So over a 1/2 cord of oak at 20 % Just for trench heat loss .
I think this should be on the notes of testing heat loss specs . and what GPM and what temp there testing it at . I'm seeing lot of smoke and mirrors on trench insulation values .
Heat550 .
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I didn't have time to check your math but I do know that some manufacturers do list the gpm and ambient temp along with the heat loss. I know badger does, maybe Z supply.
There needs to be a standard method though so you can realistically compare between the different options.
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Trench heat loss can be quite variable. It should not be very deep. Keep the trench as dry as possible. A wet trench will draw the heat away from the headed pipe and heat the surrounding ground. Drain the bottom of the trench with perferated drain pipe cover with 6 inches of 1 inch gravel. Place a heavy vapor barrier in the 18 inch wide trench and add 6 inches of 1 inch gravel. Place heating pipe in middle and cover with another 6 inches of 1 inch gravel. All gravel near heat pipe should be kept dry to act as insulation. Cover with vapor barrier and 4-5 inches of soil. The pipe with the highest R value is well worth the extra cost if you want to burn less wood.
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Great point. The soil surrounding the line often gets ignored.
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Definitely want to use clean gravel (not base rock with a lot of fines) under, around and over your lines.
Crushed limestone or clean screened creek gravel (if it is sized also) works well.
I have heard of people using sand (not sure if it was lime sand or river sand) but I would not recommend that.
Sand retains moisture much longer than crushed stone/clean gravel, you need something that the moisture can pass through.
What is available locally varies though of course but it's worth seeking out whatever will work best.
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Sometimes you don't have much of a choice. I had to put weight on my logstor to get it to sink to the bottom of my trench when I installed it because my water table is about 12" down from the level of my yard. I backfilled with the existing dirt that I dug out as gravel would simply allow the water to stay against the pipe. It would become the drainage path for all the water from the back of my house to the boiler. I buried a drain pipe below the logstor from my foundation drain to hopefully catch most if not all the flow of water from around my house, but I know the water table is extremely high in my area. I have a friend a couple miles away that has a 25' deep shallow well that has never gone dry in the most severe drought since it was put in back in the early 1900's. We're along a river and it's all old clay river bed. Absolutely no drainage through it, water just sits on it and flows under the surface down to the river. Total loss over ~60' is less than 1°F I don't think I'll get any better than that.
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I'm going to try and do rocks below the insulseal for water drainage.
Whole trench is at slope.. away from house. Rubber matting like roof
Over insulseal to divert water down to sewer rock . ( What water does get thru ) and insul seal incased in sand to keep dry . So I'm just to point of digging trench and dealing with obstacles in my way.
Thanks for the great ideas. Once I dug I realized I dealing with super wet heavy clay . It's the kinda clay that don't dry out. Not a low spotjust clay that hold water big time. I will post some pics soon when I get farther. It's pretty wild putting logstor in water and that little of loss it's great . I went with insul seal do to I have a straight shot to the house . But yes heavy clay in our area really something but if I treat it more like drainage area under insulseal I think to best I can get. Pics to come soon . Thanks for the input and info and findings it's highly appreciated..
Heat550
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Here step one. Trench has 2 inch drop every 10 feet total length 75feet.
Heat550