R value is cumulative and does not depend on distance from the heat source. Foams have some of the highest R-values per inch available, and cost like it. If correctly done his proposal makes sense. You need a very good seal at the outside of the foam to prevent moisture entry since it will act as a second vapor barrier. Luckily most of the vapor in a crawl space comes from the earth and not the interior. Air infiltration casuses a lot more heat loss than less than adequate insulation.

Although the pipes are defined as "in the slab" that is a slight misnomer. They can be said to be "in the slab" in the sense that once the slab is poured it would require cutting inot the slab to access the pipes but in actuality the pipes are laid in the subsoil under the slab prior to pouring the slab. Both the International Residential Code and the Uniform Plumbing code require that whenever a pipe is run through a masonary material the pipe is to be sleeved with a section of sched.40 pipe at least 2 nominal trade sizes larger that the desired pipe, however some local codes will allow pipes stubbing up from underslab to be sleeved with light guage flexible PVC tubing to prevent direct contact between the pipe and masonary material. The pipes both above and below grade may be insulated with standard foam pipe insulation and in some jurisdictions the foam pipe insulation will be accepted as a sleeve when stubbing up through the slab.

I was born in 1947 and I can remember when water heaters had no insulation. They were simply an upright galvanized iron tank with a gas burner on the bottom in the same manner as the internal vessel in the modern water heater and water heaters were typically operated at 180degF. (My cousin Robert still has permanent burn scars on his face and shoulder from running into a water heater when horseplaying as a small child.) In those days water heaters had no T&P valve. Instead they had a "Blowout Plug" that would literally blow out of the tank wall when the internal pressure exceeded 150psi. (They worked in the same manner as the freeze plugs installed in automobile engines.) Water heaters had a thermostat on the gas control but there was no thermocouple or flame sensor so if the pilot flame went out and the thermostat called for heat it would blow raw gas into the house. I can remember many occassions when we would come home after being gone for the day and the moment the front door was opened someone hollered "GAS". That meant that the entire house was filled with the smell of Natural Gas, so Dad would open the front and back door and we would all sit in the car across the street for an hour or so till the house vented out praying all the while that the gas in the house would not be ignited by the fire in the old coal furnace, which would then produce an explosion and probably level the house. (These type of accidents were quite common in the early 50's). I can remember when water heater manufacturers were advertising they were on the cutting edge of Space Age Technology with insulated vessels and thermocouple protected pilot burners, of course the insulation blanket was a mere 1/2" of fiberglass with a sheet metal shell over it. Tank walls were still plenty hot but at least you wouldn't receive 3rd degree burns from touching one. Oh, by the way, did I forget to mention that most water heaters had no flue pipes in those days either? They simply vented into the room but that was no problem because in those days fuel was cheap and state of the art construction techniques in those days left so many cracks and crevices that on a cold winters nite you could sit in the living room and watch the drapes moving from the cold drafts around the windows. I find it very interesting to note that during the Viet Nam conflict we were supplying millions and millions of gallons of Jet fuel, Diesel Fuel and gasoline daily to the war effort and yet gasoline was only $.30/gal on the pump and Natural Gas was so cheap that it was commonly thought of as an industrial surplus yet within a year after we pulled out of Viet Nam we had a "Fuel Crisis" where the price of gas jumped to $.75/gal and we had to wait in line to get a meager 8 gal. One would think that when the war ended there would be plenty of fuel for civillian life. Is it possible that the oil companies had lost their Million gallon a day military customer so they now decided to raise the price to keep there profit margins the same? Oh, and don't forget, for every price increase the oil companies got the state and Federal Govt padded in their little tax increases as well, Ah, but thats another topic altogether. Suddenly "Fuel Cost" was a household word and everyone began to tighten up. Houses were being insulated and caulked, speed limits reduced and we began to be concerned with "Standby losses" from water heaters. As the houses were tightened up it became necessary to make water heater flue piping a code mandate and people were encouraged to add "insulation blankets" to their water heaters. The problem with insulation blankets is that if they are improperly installed or if they slipped out of position it restricted combustion air to the burners and we began to see a severe increase in carbon monoxide poisoning in the home. As a result the Codes were again revised mandating that all water heaters MUST HAVE a minimum R-12 insulation. To meet the new standards the water heater manufacturers discontinued the use of fiberglass blanket insulation and began using cast in foams some of which are now providing as much as R-35. The Codes now state that insulation blankets are no longer required and it actually discourages the use of blankets. In fact, many local codes now prohibit the use of insulation blankets on water heaters.

Hmm, those all sound pretty bad - I'm not sure I care about the water being warm *that* much. I tried really hard to get the rubber insulation under, and I think if I used a little more force, the insulation would have torn apart. There's another alternative. What If I wrap most of the pipe, but not all the way around? There previous owner left a 6 inch pice of foam insulation on the pipe that about 80% on there. The slit is facing the wall, and it doesn't close all the way, instead it's hugging the wall. How effective is the insulation if it's not closed tightly? Does protecting it from the wind make a big difference?