Open loop combination heat and hot water system
Posted by Julian Craddock on May 01, 19100 at 14:58:19:
I currently use my hot water tank to provide hot water for domestic purposes and to heat my home
via a coil in a forced air furnace. In the future I would like to extend the system to heat the
water for an outside hot tub. I would also like to add a central air unit. The current hot water tank is a
low/mid efficiency unit and I would like to replace it with a more cost effective solution. I live in
Ottawa Canada , I am on well water, and currently use oil although natural gas is available. I am
currently aware of two options: 1.) Use a high efficiency storage type heater (polaris or similar), or
2.) A tankless heater such as an aquastar. I am interested in more information on the following:

1.) If I use a tankless heater do I also need to use a storeage tank. If so, do I loose the efficiency
benefits of the tankless system?

2.) 140F and 180F are often provided as the target water temperature. In a hybrid solution, what is the
ideal compromise/target?

3.) If I use an efficient storage heater am I better off to go with a boiler? If I use a boiler can I also use it
to heat my domestic water or do I end up with two tanks? Should the domestic water and heating water
always be kept seperate?

4.) I currently vent the oil hot water heater with a side shot. It is noisy. Can I vent a tankless solution with
straight PVC out of the wall? Up a chimney? Do I need double sided piping? How about a high efficiency
storage tank solution?

5.) The current solution uses a couple of check valves to stop the hot water cycling through the heater
coil (I leave the fan on year around). They do not work well in that the water still cycles (perhaps they
get clogged, or are not installed properly).

6.) With regards to tankless solutions are there opinions on the most appropriate model (e.g, Aquastar,
T-K1, Targa [is this still available?])?

Thanks in advance, Julian.

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