I've been considering wrapping my hot water pipes in my crawl space to save energy and quicken the hot water in the sinks. I have a propane water heater at one end of my house so the hot water takes a long time to arrive at the other end (upstairs bathrooms). Just wondering if energy saved (showers should save a little) is worth the effort (crawling under the house) and expense (foam pipe wrap).

 

It's not going to change anything.
There's still going to be unheated water in the line.
About all it's going to do is there may be less condensation dripping off of it.
Adding another heater that closer, installing a circulating pump, going with a tankless that's closer is some ideas to get hot water faster.

 

Joe is correct that insulating the pipes in your crawl space will have minimal effect upon the time necessary to get hot water to the faucet but that does not mean that you shouldn't do it. The insulation WILL help hold the heat during the time the water is flowing and THAT can save energy. The unfortunate part is that most of the "pipe insulation" sold at the consumer level is only slightly better than useless. The foam rubber, 3/8 inch wall tubing that is so prevalent at the mega-mart homecenters will not even pay for itself in terms of energy savings over an extended period of time. At the very least use the the 1/2 inch wall material with the smooth surface rather than the pebbly surface. Much better, if you live in or near a big city, find a commercial insulation supplier and use rigid fiberglass pipe insulation with at least one inch thick walls. Get the special tape for the seams as well and the plastic covers for the tees and elbows. It WILL be more expensive but it will also work far better than the el cheapo foam rubber.

 

You could be very lucky but let me tell you my experience
I used the black foam stuff saw no difference to speak of, took it off and insulation that goes in walls no change ,put more insulation around it and still have not seen enough of a savings or change in water being hot quicker at faucet than before I did anything
A lot of time and labor for very little gain.
I will say mine lines are under the house and some are in the air some on the ground
We have propane and have not seen any drastic change in doing anything
If your house is not completely underpinned I would do that which is quicker and will help just as much
If you are bent on doing it anyway I would go with the suggestion Frud has made and use the rigid fiberglass type. You see this around a lot of water lines in industrial buildings it is white wrap with the yellow fiberglass insulation inside it

 

I just crawled into the crawl space to seal my gas fireplace pipe and electrical (cold air was blowing in there) and decided to measure how much insulation I need for the pipes. Had the wife run the hot water for 30 seconds when I was under there and the 3/4" hot water pipe heated up very quickly (about 10 seconds). It also cooled off very quickly so I do think a lot of heat is lost in that bare copper pipe. I have a long run of 3/4" hot pipe of 47 feet long. Think I will order some 1" thick foam pipe insulation. Not sure if I will also do the 1/2" feeds of that main line yet but I think it will pay for the cost of insulation pretty quickly.

 

I think if you seal where the cold air is coming in at will be a bigger savings than insulating
True your pipes may stay hotter longer but you will never see enough of a savings to buy a night out at the local burger joint.
Doing it for peace of mind is good and it may make a good resell point down the road
If you are bent and bound to do this, then do not waste time buying the black foam looking stuff from a local DIY store.
Ask them if they can order the yellow fiberglass or the pink with the white paper type outer covering. If they can then order that
This is the only kind that is going to give you a chance of a savings return
The black foam is simply for help to stop from freezing
Keep in mind that is the purpose of most pipe insulators not for saving on cost but to stop pipes from freezing