Installing Underground Boiler Piping

I'm installing a coal boiler in my garage (Chappee Hand Fired Boiler) and I need to run the water pipes about 100 feet underground back to the house. Insulating the pipes is the big problem with this scheme. I had thought to use a product called Maxx-r which is designed to hold two 1" pipes and maintain temp drop less than 1/2 degree per 100 feet. The web pages I looked at seemed to say the stuff sold for 9 to 11 bucks for eight foot sections. Wrong. I tried to order it and its 9 to 11 bucks per foot ???? I really don't know who can afford that, certainly not me. Anyway I'm trying to come up with alternative insulation methods now.

I thought to use 4" corrugated drainage pipe, put the 1" pex in that and center it up using those kabob sticks from wallymart that come 100 to a pak for a buck. I planned to then squirt spray foam insulation stuff used to fill cracks and such into the drainage pipe thru the holes. It seemed like a good plan but I tried a 10 section for practice--it works really well, it just takes one $5.00 can for every two feet. . .again over by meager budget.

Anyone have any creative ideas?

From what I've been reading, a lot of your options are going to be in short supply. I bought 100' of pex-al-pex double wrapped foam/alum coating. It came in 4" seamless corrugated pipe, and was about $600 shipped from a supplier on Ebay. I put that in a 6" seamless corrugated pipe for even more waterproofing and R value. It seems to be working very well. My run is about 85' one way. With this mild weather, I'm loosing about 1 to 1 1/2 degrees from the coal boiler through the oil boiler and back to the coal boiler (when there is no call for heat or DHW).

Last week I buried some home made insulated Pex. I could not get the Pex-alpex that I wanted so settled on 1" oxygen barrier pex. It will only move about 50,000 BTU's compared to about 80,000 for the pex-al-pex, but I'm running two sets so should be fine. What I did: put foam insulation on each pipe.... you don't want to lay the bare pipes together, expecially on a long run. The return will cool off the supply. After each pipe had a layer of the insulation I taped them together and wrapped them with a layer of foil bubble wrap then put them inside 6" schedule 20 PVC. I put the black insulation on all the pipe, then did the foil 10 feet at a time. I'll let you know in a few months how it works.

If you use PVC, make sure to use cleaner and glue, especially with schedule 20. You must insure that water can NOT leak into the PVC as it will make the insulation zero. My PVC goes slightly downhill and I put a clear plastic tube going from the bottom of the PVC to the boiler room. I can tell if it gets water in it by sucking on that tube. If for some unknown reason it does leak I will see to it that it stays pumped dry.

I used 8 inch schedule 40 PVC well casing for my conduit. It contains my insulated copper supply and return, two PVC electric conduits plus a PVC potable water pipe. I've got two 90 degree turns. I took 8 inch 90 deg els and cut them in half clam shell style on my table saw. I used PCV glue to half the the els in place, then installed my piping and covered the corners with the other clam shell half. I used silicone RTV to glue the top half on and fill the saw kurf gap. My total run was about 40 feet.

The 8" sch40 pipe would be great, but the price for that option puts it right out of reach. The maxx-r product basically puts 3/4" closed cell foam around the pex which yields about an R5 value. Its price is also right out of reach. Freddy, it sounds like your methods are along the same lines I'm thinking, but could you explain what you mean by "move about 50,000 BTU's compared to about 80,000 for the pex-al-pex?" Isn't the btu/hour flow through tubing related to the gallon/min. rate as well? I would hate to think the 130kBTU of the boiler would be trapped out in the garage! I also purchased the oxygen pex from the local Lowe's store as it was the best price I could find available now. The insulated pex looked like a great product as well, but it too was over my price point.

The pex-al-pex is (so I'm told) just over an inch inside. According to a chart I have, one inch can move 71,000 BTU. ( but most people say 80,000) The tubing I have is 7/8" inside. My chart does not show 7/8, but it shows 3/4 as 39,000, so I'm fudging a guess that 7/8" can handle about 50,000. That being said, a larger pump can drive more BTU's, but I'm not familiar enough with the science of it to know what pump and how much more it might push. I do know that my house will heat with a steady 50,000, and that I have two sets of pipes, so I'm not worried. I'd have bought a smaller Axeman if they made one! My oil boiler is 165,000 BTU, I never worried about the extra size, I just down fire it & it's fine. Certainly if you're going to use a particular pipe you should have an idea of the heat loss of your house.

PS. I got the 6" schedule 20 for $14 a length at a wholesale place and the fittings at Lowes for $7 each. (Lowes wanted $34 for the pipe and the wholesale place wanted $14 each for the fittings!) I used two 45's to make my 90 degree bend. That was quite difficult, no way would it have gone through a 90. I had to stop the foil bubble wrap at the 45's and continure it after them. It was just too tight to go through. I actually did not put the pipe through the fittings, I put the fittings onto the pipes.

That last pic looks like it was taken at night...burning the midnight oil out their are we?

coalmeister wrote:burning the midnight oil out their are we?

Ummm, I think it was 10-30 oil.

Thanks Freddie, that sounds like something I need to understand better. I just located some of the closed cell rubber type of insulation for the pipe, but I only ordered enough for a single run of pipe, not two. I'll be digging around for some more info on heat flow now.
John

OK. Thanks for the pointer on the heat flow capacity Freddy. I work at an engineering school so I pressed my problem onto one of the mech faculty here. It looks like at 100 feet and 130kbtu I want 1.5 inch pipe or two 1 inch pipes like you used.

I had no idea
In part, here is his answer:
"The equation for hydronic heat flow is : Q = 500*gpm*(t out - t in). Assuming a 30 degree tepmperature difference i.e. 180F out and 150F return then for 130,000 BTU per hour you would need about 9 gpm flow rate. I would recommend a 1 1/2 inch pipe for that to keep the friction drop in the pipe down and reduce pump energy required."

It comes down to the amount of flow required per minute in the pipe. I could use a bigger pump, but then the power costs would eat up the energy savings

I'm back to the trenches looking for more pex and more of that black insulation stuff now.
Thanks again for the heads up.
John

Just an update on my piping progress. I went back to the drawing board and purchased 400 feet of 1 inch pex. Each 100' pipe I put 3/4" insulation jacket over (r 4.7) and pulled that through four lengths of 100 feet of flex drainage pipe--the 4" corrugated stuff, but the kind with no holes or slits in it. Buried that all about 4 feet down between the house and the garage. The open ends of the flex pipe I sealed off with spray foam which protects the large pipe from being crushed where it comes up out of the trench under the house. I laid sections of 1/2 inch foam board over the top of the pipes before I buried them, but that was more to protect them from rocks than for insulation. The price of the solid schedule 40 pipe is 16 bucks for a 10 foot section which would have increased the costs of this science project by over $650. Pex, insulation, and drainage pipe and some spray foam came to about $950, so counting the crimp fittings and maybe the gas for the back hoe, I have about $1000 in the buried pipe. Oh yea, $35 more for grass seed

I'm on to the chimney construction now, trying to scrounge some stainless pipe from around the research labs here maybe. . .

I wish I had pictures. When I installed my OWB 5 or 6 years ago I pulled 4 1" Pex pipes through 100 feet of the corrugated drain pipe like you. For insulation I used carpet padding that had just gotten ripped out. I get about 3 degree loss in temp the best I can tell.

Here is my experience with underground runs:

I used two runs of 3" sch 40 Electrical conduit between my two buildings which are about 30' apart. I used one run each for supply and return as the ID of the 3" was ideal for 1" pex with 1/2" insulation. Electrical conduit elbows are long radius and allow for a smother bend. I was able to shove the pex through by making a tapered wood plug I taped in the end to prevent the square edge of the pex jamming against the joints of the electrical conduit. I preinsulated the pex by sliding 1/2" foam insulation over it and taping the joints with duct tape. A large single conduit could be used with similar results. The key was the long radius elbows. I would recommend a pull rope for pex runs longer than 30' as it would be easier than trying to shove it through.

As for capacity, normal design of a heating system is for 20 degrees differential in water temperature. Higher drops can be used by sizing the heating equipment accordingly. PEX has the same capacity as equivelant dia. copper tube. Normal design pressure drop is 3 to 4 feet of head drop per 100 feet of pipe. A 1" pex can handle about 7.5 gpm max at this design. Therefore you can get about 75 MBTUH at 20 deg. delta T and 112.5 MBTUH at 30 deg. delta T. for a 1" pex at 7.5 gpm. Getting more than a 30 deg. delta T is difficult and requires very careful sizing. I pump to my workshop through 100' of pex and about 10' of iron piping each way. I use a Taco 011 pump and have no trouble sucking all of the heat from my 110 MBTUH boiler. Note that the Taco 011 pump is probably a little oversized for my application as I have future repiping plans that will need that pump.