As a side note, I ... along with a few other ... are really getting fed up with the short session expiration times on this site. I wrote this once already but had timed out by the time I finished and had to type it all over again. Yes, I know I wear perform proper protection before trying to become intimate with this site but the 5 to 10 minute timeout is ridiculous. MODERATOR\SITE OWNER please take note
Back on point ...
I live in Prior Lake Minnesota so the environmental conditions are similar.
A few years ago on a very cold January morning I was forced to turn the water off using the curb stop. This is the valve that is buried in the ground and is between the water main and the house. I made a homemade curb stop wrench that was over 6 feet long and only about a foot of it was sticking out of the ground when I got to the valve. I was surprised to find slush at the bottom of the hole. Not water and not ice, but slush. This suggested it was much colder at 60" than I thought it would be.
If you Google "Minnesota frost line" you get stuff like this
1303.1600 FOOTING DEPTH FOR FROST PROTECTION which indicates 42" in the south half of the state and 60" in the northern half of the state. Your 48" trench would seem to be "just barely adequate" in my opinion, but then again I usually over engineer as it is cheaper to go down another foot now that is is to dig it up or thaw it out later.
I also do not think insulation will totally mitigate the risks unless there is a reasonably regular flow of water thru the system. Insulation will not make things warmer, it will only slow the transfer of heat from the warm to the cold. In this case the warm will come from the water flowing thru the system. If no water flows thru the system for an extended period of time I would thing the system would eventually reach equilibrium at a temperature that matches the ground temperature ... which might be cold enough to freeze the water. Obviously the time coefficient to reach said equilibrium could be longer than the water usage pattern and it would never freeze up ... similar to when people use to leave a faucet running at a very low setting to keep the pipes in the house from freezing up ... but still it is something that I would think about.
Got the gas line, here was my experience. My main gas line comes from the outside meter to a regulator near the furnace. The regulator reduces the pressure from the "high pressure" of ... I am told ... about 2.5 psi to only a few inch psi. This then flow to a manifold that feed the stove, the furnace, the water heater and the dryer. The stove is 3/4". the dryer is 1/2" and the furnace and the water heater are 3/8" copper. The stove is a 35 foot run, the dryer is a 20 foot run and the furnace and water heater are less than 10 feet.
When I added the 75,000 BTU heater in the garage, a 60 foot run but all inside, I used 3/4" copper that started on the "high pressure" side of the main, before the "manifold regulator". I then installed another regulator just before the heater in the garage. If I recall correctly I had some trouble finding a local source for the regulator as I was not "certified" to do any work on the "high pressure" side of the line. I eventually worked it all out ... and old age may have clouded the memory ... and your experience may be different ... but that is how I recall it happening.
Arvid
