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Old 01-08-13, 10:17 AM   #21
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I have thinner copper pipe than what is coming out of the water heater as it makes its run to the bathrooms, not sure the size but I think it is half inch coming out of the water heater and I had bought four lengths of 3 foot(1 meter) pipe insulation and insulated three feet on the cold line going back towards the water softener which is warm pipe when the water is stagnant. I then insulated 9 feet or 3 meters from that point towards where the pipe joins the smaller runs to the kitchen and bathrooms. I have taken a one gallon juice jug and it takes 3/4 gallon to get hot water to the shower faucet which is also the farthest length away from the water heater.

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Originally Posted by Snail View Post
I've just replumbed my new-old house with small-diameter plastic piping. Longest pipe run from the central in-line condensing gas water heater is about 12 metres (40 feet). I just completed the wiring to the heater a day or so ago. The hot water comes through faster than the much shorter 3/4 inch copper pipe runs at my existing house and there is no problem with pressure loss in this mains-pressure system.

I ran some calculations on insulation. Given that you are going to loose all the heat in the pipe fairly quickly, regardless any insulation and given that even in a windly crawl space and with a 10 meter run of copper pipe the rate of heat loss from the hot water in the pipe to the air is at least an order of magnitude lower than the 10 to 30 kilowatts being supplied by your heater or cylinder whilst the tap is being run, complete pipe insulation is a waste of time and money in my climate. If you had a freezing blizzard passing the pipe and you were using the tap at the end of a long run at frequent intervals it just might be worthwhile I guess. So do the calculations first!

If you have a hot-water storage cylinder, heat will be conducted from the cylinder along the pipe at all times, not just when water is flowing, So in this case, you need to insulate the pipe from the cylinder for a meter or two, so that the loss from this cause is low compared to the general losses through the cylinder lagging.

Peter
In cold climates like mine, people don't put their pipes in windy crawlspaces, they are placed inside the building envelope where it is the same temperature or very close to the inside temperature. My pipes are safe when my house is at 40 degrees and the temperature outside is 10 degrees or warmer, at that temperature the pipes are 36 degrees. If it gets colder than 10 degrees, I make sure the house is at 50 degrees when I'm gone and that is safe down to -20f or likely even colder but we don't get colder than that here normally although I think my area has had -28f/-33c once but I'm still okay with 50f/10c inside at those temperatures. Most publications say to keep your house at 55 degrees, so there is some safety factor but I've measured the pipe temperatures and the water outlet temperatures and am safe a little colder because I know where my pipes are and my insulation in my house is not deficient near the pipes. If you were gone for a long time you could always get a thermostat based electric heater outlet and run a UPS and some heat pipe wrap and insulate over that if you are worried about the pipes freezing. It wouldn't work forever but those pipe heaters don't consume too much power just get an appropriately sized UPS for the time that you are gone and if you are friends with your neighbors, have them call you if the power goes out so you can deal with it.

Regarding the pipe insulation, daox revealed that the output temperature at his far faucets was hotter and he was able to turn down his water heater thermostat after adding pipe insulation. If you have multiple people in your house and your showers aren't as short as mine, it might be a good idea to use it if it means you can drop your water heater temperature down a bit. I have my water heater set to 130 degrees to get a 15 minute shower at a temperature that is as hot as I want it with a 1.5gpm shower head that actually uses 1.8gpm. Oddly enough when my house is hot in the summer and the a/c is off I can have the temperature in the water heater MUCH colder than when I get home and turn the thermostat up and the house is still 50 and getting warmer when I take a shower. In my case I might insulate the accessible pipes and turn down the water heater. Also in the summer I went an entire two months(the hottest ones) taking daily showers with the water heater thermostat all the way down and was able to do it purely on the heat from the pilot light, believe it or not. 4 therms for multiple months, that's shared with using the stove so it might otherwise have been 3 therms. I pay 65 cents a therm. I can't do that in the winter though the tank cools off too fast, even with the house at 70 degrees but 80-90 degrees(30c) I can get away with it. I have a water heater insulating wrap that I got and will soon have on the heater and if I add insulation to the pipes, I think my usage will be lower. It will especially help as I have two more people moving into my house that will probably use plenty more water in the shower than I will. Pipe insulation is cheap. I think I paid $10(max, but I might have paid less) for 12 feet or 4 meters of pipe insulation when it was on sale. I want to find some thicker stuff though for the run to the shower this time around but I don't see it at the hardware store but I will probably check a few more places to see if I can get thicker stuff but in reality, I don't think it takes much to make a dramatic impact.

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Old 01-08-13, 10:53 AM   #22
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I am adding this just for more ideas if they fit your situation. I live in eastern NC and the temp rarely gets down to 20f at night and most days goes back to 40f or above. In order to fix, so to speak, my hot water issues I did several things that some thought was unconventional.
Originally when I bought the house the hot water tank was in the garage, 15' from the kitchen sink and 40' from the bathrooms. While remodeling Ibought the highest efficienct 40 gallon tank available and placed it in the attic driectly above the bathrooms. I did put a drip pan beneath drained to the exterior and also plumbed the relief into the drain line. I insulated all pipes in the unconditioned space. This serviced only the bathrooms. I then bought a 10 gallon water heater and placed that in the crawl space beneath the kitchen sink.
This made hot water almost instantly available in both location. Eliminated losses in long pipe runs. In the summer time I do get the benefit of some passive heat gain on the tank in the attic. Almost no water waste at the kitchen sink as well.
Works for me and seems to have been a good decision.

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