A common argument against the use of tankless water heater is that it will take longer for hot water to reach the point of use. Technically the assertion is correct but the difference is likely only a second or two maximum. The distance of pipes running from the water heater to the tap is the same distance whether it’s from a 40 gallon tank or a tankless water heater. The entire volume of cold water contained within the pipes needs to be emptied before hot water can flow from the tap. This is especially true in the mornings or after long periods of time where the water in the pipes has been sitting and lost all of its heat to the surrounding environment.
Reducing the heat loss by insulating hot water pipes allows your bathroom taps or kitchen faucet to get hot water neatly instantly utilizing the existing hot water contained within the pipes. Ensuring that all your hot water pipes are insulated maintains the heat much more efficiently and for a greater period of time.
Most pipes are made of copper and copper is a fantastic conductor, this works out to be a negative attribute as it allows for very quick heat loss from your hot water pipes. Pex piping is becoming more common now and is a plastic piping system. Heat transfer from plastic is significantly reduced when compared to copper but heat loss is still substantial enough to justify pipe insulation.
We did an experiment to show you how much heat loss occurs from both Pex pipes compared to copper pipes. Then repeated the experiment and compared the two when they were insulated. We used a tankless water heater in one of our homes, the water temperature was set at 120 Fahrenheit at the tankless water heater and the pipe temperature was measured with a laser thermometer on the exterior of the pipe.
Insulating Hot Water Pipes Test Result
Starting temperature of the basement was 60 Fahrenheit (15.5C)
Water temperature from the tankless was set at 120 Fahrenheit (48.8C)
Tap water reached 116.9 Fahrenheit (47.1C)
The tap was running for 5 minutes
After hot water had passed though the pipe and exactly 1 hour allowed to pass the exterior temperature of the uninsualted copper pipe was 62.1 Fahrenheit (16.7C).
And after the hot water passed and 1 hour allowed to pass the copper pipe had a temperature of 69.1 Fahrenheit (20.6C).
The Pex pipe had an initial reading of 60.1 Fahrenheit (15.6C) before the hot water was turned on at the tap.
After hot water had passed though the pipe and exactly 1 hour allowed to pass the exterior temperature of the uninsualted Pex pipe was 63.1 Fahrenheit (17.3C).
Again the insulated Pex pipe had a temperature of 60 Fahrenheit (15.5C) before the hot water was turned on at the tap.
And after the hot water passed and 1 hour allowed to pass the Pex pipe had a temperature of 79.6 Fahrenheit (26.4C).
The results were not what we had initially predicted. Although once we talked it over we discovered why the insulated copper pipe was much cooler than we had anticipated. Unfortunately for this experiment we only insulated a 10 foot section of copper pipe the rest was left bare, we determined that since copper is such a great conductor the exposed pipe would work to cool the hot water within the insulated section faster than if the whole length of pipe has been insulated. The Pex pipe saw a much higher temperate because plastic doesn’t transfer heat nearly as well, thus the insulated section was able to retain heat more efficiently.
Going forward we would highly recommend insulating hot water pipes throughout your house. It is sufficiently important in both homes with tankless water heater as well as homes using conventional water heaters here in Ontario.