Published Saturday January 19, 2013: Updated 9/30/2013
Hot Water Pipe Insulation
Wouldn’t it be nice to have instant hot-water available at every tap in the house?
In our home, I want to have the security, affordability and convenience of a conventional hot-water tank but still be able to have instant-hot water at each tap.
As hot water from the water heater travels through the plumbing, some of its heat and energy is lost into the pipe itself and the surrounding space. After running the water for a while, the hot water heats up the plumbing, the ambient water is purged and eventually, hot water is available for use at the faucet.
Immediately after using the faucet,
the water still in the pipes begins to cool. This is caused by
thermal conduction from the pipe into the much cooler surroundings.
Regardless of the type of water heater, there will always be some heat wasted in the pipes.
By adding pipe insulation, the energy wasted by the cooling of the water still in the pipe can be slowed down. The inconvenience of waiting for more hot water is reduced.
With perfect pipe insulation, the hot water in a pipe could remain hot indefinitely. If money were not an issue, using Aerogel insulation would keep the water in the pipes hot for weeks. But let’s be realistic. While my labor (at home) is cheap, my budget for this endeavor is only $50. Let’s see how far I can take this with conventional pipe insulation.
|Insulation Material||Energy lost (English)||Energy Lost (metric)|
|Bare copper Pipe||200 BTU/hr-ft||192.3 watts/hr-meter|
|Foam insulated pipe||20 BTU/hr-ft||19.3 watts/hr-meter|
|Dynamic Vacuum Pipe||4.0 BTU/hr-ft||3.9 watts/hr-meter|
|Cryogenic VJ Pipe||0.45 BTU/hr-ft||0.43 watts/hr-meter|
Insulating Pipes (Single layer)
The short answer: Pipe insulation is a worthwhile venture. I spent $18 in materials.
Our water heater is located in the center of the basement and the plumbing branches out in either direction. The kitchen on one side and bathrooms on the other. I added pipe insulation to just the hot water pipes on the bathroom side of the house. The plumbing is no longer accessible on the kitchen side.
I should have done measurements before the insulation was added but I forgot. Instead I compared the performance of the insulated bathroom section against the un-insulated kitchen section. Both runs are nearly identical in length and water volume.
Before, insulating the pipes, the water would get uncomfortably cold (for washing your face) within 30 minutes. After that, purging the pipes with new hot water was necessary. To make matters worse, most of the master bathroom plumbing runs along an exterior wall. The cool-down time is very short in the winter time.
After insulating the hot-water pipe, the water stays warm enough to comfortably wash your face with it, (even 1 hour 20 minutes later).
Insulating the hot-water pipes made a big difference in comfort. If adding insulation made a good improvement, then perhaps adding more insulation will be even better.
Double Insulating Plumbing pipes: The results are in, sort of.
On January 1, 2013, I added a 2nd layer of pipe insulation to our hot-water pipes. This 2nd layer was made out of 2 pieces of ½” foam pipe insulation wrapped around the single 1st layer of 3/4" inner diameter foam insulation. Each piece formed a half circle around the 1st layer of insulation. One of the foam pieces had adhesive edges and that would stick to the 2nd piece, forming an air seal.
I also added metal foil tape every foot to keep it all together. They sell larger diameter insulation for pipes but buying small stuff and doubling it up is super cheap.
It was kind of labor intensive and I wasn’t able to directly access as much pipe as I had hoped. But at the cost of not watching TV that night, I got it all done. There is a 6’ section of pipe that runs along an outside wall that is completely blocked by a HVAC duct. On the first layer, I was able to slide a piece of insulation over the pipe and shove it along the pipe behind the duct work. On the 2nd layer, I couldn’t do this since there wasn’t enough space and the 2nd layer of insulation wouldn’t slide over the first layer of insulation. I was able to reach all the other sections of the hot-water pipes.
This 2nd layer (green plot) definitely improved things but not as much as I had hoped. Granted it was 12 degrees F outside at the time I conducted this 2nd test. Colder temperatures probably made it perform much worse than when I ran tests late at night on November 14th when it was around 39 degrees outside. Even after running the faucet for a few minutes, the water wasn’t as hot as it was the first time I conducted the test. I added a corrected plot (purple) normalizing the data sets. It shows there was further improvement.
In any case, the cool-down time has more than doubled from the original, un-insulated pipe.
By The Way:
Here’s a bit of info about Kaysville city tap-water temperatures (most, if not all of the culinary water comes from snow pack in the Wasatch Mountains). It never crossed my mind before but it is obvious if you think about it - the temperature of tap water will vary greatly throughout the year.
|Date||Water Temperature (at our house)|
|July 24, 2012||66 degrees F|
|November 14, 2012||61 degrees F|
|January 18, 2013||48 degrees F|
Tap water is 18 degrees F cooler in mid January than in July. It takes more energy in the winter time to heat water to 120 degrees F than in the summer time. Not only that, people (myself included) tend to take longer showers in the winter because it’s colder outside and you don’t want to get out as readily.
In a 100% efficient water heater (gas ones are only around 55%), it would take 131.6 watt-hours to heat up 1 gallon of summer tap water. It would take 175.2 watt-hours to heat up 1 gallon of winter tap water.
|1BTU will raise 1 lb of water by 1 degree F||theory||theory|
|1 gallon = 8.3 lbs||Temp F||Temp F|
|delta (degrees F)||54||72|
|BTU to heat 1 gallon||448.2||597.6|
|Watt-hours to heat 1 gallon||131.36||175.15|
I could drive a mile in the Geo EV on just over a gallon of winter hot water energy. Hmmmm, I need to fix that drip in the shower.