Insulating Underground Pipes

[elliott.plack]

I have been helping my aunt excavate her back yard, in order to expose hot water pipes, that run about 30 feet from the house to the garage. Both the hot water heater and the natural gas boiler are in the garage. The pipes are not insulated and are just about 18 inches below grade, in Cambridge, Maryland (8 feet above sea level). Last year's heating bills were astronomical, and my Aunt thinks that a lot of heat was radiated into the frozen ground, before it ever reached her house.

My question is, once I expose the pipes completely, what is a good method of insulating pipes in sandy and wet soil. Cutting the pipes are not an option, thus we need something to retrofit. The insulation must withstand backfilling, vast temperature changes, and moisture. What can be used on this job?

Note: The house was built in the 1940's. In addition to fixing the pipes, my Aunt is also insulating the house's ceilings and walls.

[m Ransley]

You realy should move the boiler and water heater in the house, seriously. You had a good suggestion with foam insulation being poured around the pipes, but you will still loose alot of energy heating the outside and garage. If you can`t move it inside Im guessing R 33 might be pretty good that will equate to 6" of insulation of a foam with R 5.5 per inch rating that is a 12" form to be made. Even so you will still loose alot of heat through the pipes and the heat the boiler itself gives off. A great option is get a Rinnai or Takagi tankless water heater boiler combo, you can I believe get to 93% efficiency, that is well over the standard 80-82% of a new regular boiler, but the best part is the heater hangs on a wall and is very very small, they can fit in a closet. I imagine you could cut your bills in half or more with such a system.

[Bob]

I built a "box" for pipes going to heat my hottub out of extruded sytrene which can handle 25 pounds/square inch. I cut strips (1 wide for the bottom, 2 narrow for the sides, wide for the top) using a long straightedge and a very sharp thin bladed knife, and glued them with construction cement which was compatible with the foam. I believe the foam is R5/inch.

Bob

[SQLit]

Are the pipes even worth saving? Unprotected galvanized would be almost at the end of their useful life. Copper, may be in better shape.

I personally would call an spray insulation contractor. The two part stuff that they use is a bitch to work with if you do not have the equipment and they will give you a guarantee for their work. Spray foam will adhere to the conduit and will seal the conduit from the earth. I use this method for rigid electrical conduits when ever someone is stupid enough to bury rigid. Metal in our soil is about a 6 year life span. Once it has set up medium rocks do not even phase the insulation.

[Duane Bozarth]

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I would strongly suggest at least investigating updating the heating system and water heater at the same time as doing the insulation job instead.

An old boiler will have very poor efficiency compared to a new unit even w/o the remote location. Ditto for the water heater. She may well pay for the extensive renovations in a very short time...

[elliott.plack]

Thank you everyone for so much help! Here are answers to some of your questions:

1) The backyard will be foot traffic only. No cars or even ride on lawnmowers.

2) The pipes are all copper. 2 x 1" steam pipe. 2 x 1/2" hot and cold water. 1 x 1/2" natural gas pipe.* 1 x 1" natural gas pipe.*

• = The 1" natural gas pipe feeds the boiler/water heater and goes from house to garage and is barely 12" below grade. Is this safe? Secondly, the 1/2" gas pipe feeds the dryer and is flexible copper and is just kind of laying in the hole, with no support. The flexible pipe is bent and bowed, and was only 6 inches below grade at points. Any suggestions?

3) The water and steam pipes are all adjacent, while that gas lines average about 1 foot above them, and are separate from the water and each other. Should hot and cold water be insulated together?

4) Thanks again!

[Stretch]

I doubt the Steam pipes are steam. Most likely hot water. If steam, one will be staem and then a smaller condensate return line. There is a company that makes pipes pre insulated with foam and encased in pvc. Rovaco I think. Try that.

Stretch

[Stretch]

Sorry, it is Rovanco, Try

Stretch

[Duane Bozarth]

I'm, of course, meaning to investigate moving to a central heating system and putting the water heater in a closet or even a small additon if it takes it...

[w_tom]

18 inches is not sufficient for any pipes with water. Pipes typically should be 3 feet under for reliability, human safety, and pipe protection (even from rodents) as well as to insulate the pipes. Insulation only 18 inches down makes a perfect nest for rodents. Pipes should also be installed so that if the heat is turned off, pipes will not freeze. 18 inches is not sufficient for electric wires feeding the building. Why then would it be acceptable for heat pipes?

Meanwhile, if 6 > I have been helping my aunt excavate her back yard, in order to expose

[PipeDown]

Will the ground on top be subject to heavy loads like parked cars or an occasional delivery truck or is it strictly foot traffic or garden area.

For the lighter loads I might try expanding foam mixed from a 2 part mix and poured right on the pipes with minimal form around it to control the expansion. May even be insulation contractors who can dispense the stuff from a truck.

Simple closed foam (cell pipe) insulation would be better than nothing but may compress a bit. Maybe two concentric layers.

Here is an idea: Take a piece of 4" PVC pipe and use a router to cut a slit along it wide enough to get the hot water pipe into. Fill the pipe with expanding foam insulation (or whatever you want) and seal the slit with mastic or aluminum duct tape and bury slit side down.

I think you might also be able to cut a long section of 4" PVC pipe (along the long axis or maybe just a slit wide en

[PipeDown]

Oops,

Simple closed foam (cell pipe) insulation should read "Simple (closed cell) foam pipe insulation"

[Andy Hill]

There's at least one product (Condufill, I think it's called) that is marketed for in-place reinsulation of steam pipes. It's some sort of expanding-foam insulation that is rated for steam temps. Don't know a huge amount about it, 'tho.

[Edwin Pawlowski]

Good idea. Use the spray in foam. It gets hard enough and will stay in position so you'd not have to put the slit down. Sure would give plenty of insulation.

[Chris Lewis]

According to PipeDown :

Styrofoam SM (the blue stuff) is often used in direct burial applications.

Ie: under slabs, on foundation outside faces, etc.

I would assume it could withstand the temperatures involved here. [It's used in contact with radiant flooring.]

I suggest it because it's probably easier/cheaper than on-site mixing/installation of foam for a DIY.

If suitable, I'd recommend putting several inches of gravel, then two 8" wide layers of 2" foam, a slot for the pipes, and another two layers of 2" foam. Glue the layers/"joints" together with foam adhesive (available as a caulking tube).

A 2'x8' slab of foam is around $15 IIRC. That would do about

12 linear feet of insulation (8"x8"). What is that anyway? 4" of foam is R20, right?

Wrap it with tape to keep it from shifting if the glue is still wet, and you're backfilling.

Even at only a foot down, it should withstand considerable surface traffic, but to be absolutely sure, fling on a few treated 1x6 fence planks before backfilling. Even strips of exterior grade OSB would do. [It'll eventually rot out, but by then the soil will be compact enough to not crush the foam.]

A building supply house that's "advanced enough" to know and supply the various grades of SM available (ie: under slab vs. interior wall etc) would be able to advise you which grade is right for this, or whether this is a dumb idea.

[Chris Lewis]

According to :

I wouldn't take w_tom's comments about burial depth _too_ seriously, other than considerations for frost depth. Especially since you have a cold water line here, you need to check that 18" is _below_ your frost line. It might be. But it certainly ain't here (it's more like 60" here).

18" might be enough for Maryland, but I don't know.

I don't know what the gas line burial requirements, but 6" seems awful shallow.

[Edwin Pawlowski]

Why do you doubt it is steam? Make a lot of sense to me as steam can easily deliver a lot of energy at some distance compared to water. Many buildings in large cities do not have any heating systems, but rely on steam generating plants to deliver the steam to them and distribute it through the building. I do agree that 1" copper seems a bit small for the main distribution at residential pressures.

If the pipes are steam, they will be in excess of 215 degrees. that rules out the use of most foam plastics for insulation though. Go with a mineral or fiberglass product.

[Elliott Plack, USAR]

You are correct, they only have hot water in them. Thanks

[w_tom]

18 inches in unacceptable even for water pipes in Maryland AND unacceptable for buried utilities. Furthermore, 18 inches is not sufficient to protect those pipes. Again, even superior grade insulation must be at least 6 inches for spaces that are at lower temperatures than that pipe. Two reasons are provided in that sentence that says others are recommending only minimal (marginal) insulation. Insulation installed shallow in the ground will not be as sufficient. If putting less insulation on those pipes, then don't even bother with more than 2.5 inches in the attic - heat losses in pipes close to the surface will be that great.

This little amount of insulation on that heat pipe is for pipes that remain in about 50 degree F earth. Pipes are buried deeper also so that temperature is closer to 50 degrees. Earthing at just under 1 foot is colder and requires significantly more insulation than others have recommended. A pipe in Maryland should be buried deeper as is standard for other utilities - if for no other reason because others recommended so little insulation.

How deep the gas pipe? This is often a function defined by the local gas company.

Greater burial depth is for reliability, safety, code requirements, and so that pipes can be so lightly > I wouldn't take w_tom's comments about burial depth _too_ seriously,

[YouRepair.com]

I would have to agree 18" is not deep enough but additionaly a run of

30 feet is a bad thing.

Even if you were doing this the other way around and heating the garage hot water from a heater that is inside the house it would still be very wrong.

the frost line in md is 36"

i am sure this has probably worked for a long time but you are probably losing a lot of heat.

I would immediatly find a cost sheet that shows price averages for your area using your type of system and compair the difference.

Call the gas company and they will help with information on average heating costs and may even send someone out to look for free.

I strongly suggest that you think hard about getting the water heater into the house this season. At worst maybe you can cap the hotwater line comming into the house and attach the hotwater heater at that point.

but call the gas company they may even give you a rebate coupon to buy new stuff if not ask if the state will.

best wishes