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Community and Q&A

Is it worthwhile preheating the cold water supplying a domestic water heater?

JBrinkman | Posted in Mechanicals on

I will be building a new home this year in northern Ontario, Canada. The intention is to build a very efficient home with high insulation levels. While I have the design essentially complete I still have not determined how to heat my house. The house will be south facing on a slab with a second storey, I am leaning towards radiant heat. Infloor on the main and radiant baseboards on the 2nd floor.

I am looking at using a well insulated storage tank for the heating purposes, if I was to run my cold water supply for the water heater through a coil in this tank prior to entering the water heater in order to help preheat it can it increase the efficiency of the water heater?

Would I be better to utilize an indirect domestic water heater using the boiler and a well insulated storage tank?

Would it be worthwhile to use a heat pump water heater for this application? Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    There may be some good reasons to install a well-insulated storage tank to hold water in your home. However, whether the water in the tank is used for space heating or domestic hot water, it won't be hot water unless you have a way to heat it. There are lots of ways to do that -- you can use a boiler, a water heater, a heat pump, or solar collectors -- but you still need to heat the water if you want to use the water in the tank for space heating or domestic hot water.

    Assuming that you use fuel (propane, natural gas, oil, firewood, or electricity) to heat the water in the tank, then running your cold water through a coil in the tank before the water goes to your water heater won't save any energy, unless you can find a way to heat the water in the storage tank in a way that is cheaper or more efficient than the way your water heater works.

  2. jklingel | | #2

    Search for "programmable thermostats, part II" on They have an article on boiler efficience and return temp that you may find helpful.

  3. JBrinkman | | #3

    Thanks for the replies and thanks for making me aware of the healthy heating website it is going to be very useful.

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