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.
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.
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.
Thank you everyone for so much help! Here are answers to some of your
1) The backyard will be foot traffic only. No cars or even ride on
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
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!
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.
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.
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
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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 insulated as
others have recommended. 18" is rarely deep enough in cold
weather states - except where the installer does not care.
Chris Lewis wrote:
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
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.
I would strongly suggest at least investigating updating the heating
system and water heater at the same time as doing the insulation job
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...
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 inches of insulation was not sufficient for
the house, then why would anything less be sufficient for
pipes that are even hotter? Let's assume those pipes have 6
inches of insulation. That means less than 1 foot of dirt?
To be effective, the insulation must not compress which is
another reason why the pipes should be deeper - not subject to
compression forces of overhead traffic only 1 foot away.
Actually you can get by with as little as 12in. in a residential setting.
See table 300.5 in the 2005 NEC (column 4).
For direct burial circuits at 240 volts you would have to go to 18in.
I complete agree however that the water lines need to be below frost depth.
Three feet at least.
The best answer is to move it into the home or to an addition attached to
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
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
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, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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