Using Your HWT for In-Floor Heating
Here are three ways you can use the hot water tank (HWT) to heat your home and the benefits or drawbacks of each method.
1) A Stand Alone HWT: This means you have a separate tank that is used only to provide hot water to in-floor radiant heat systems, radiators, fan coils, or other heating methods that require hot water. The hot water for your home is a completely separate HWT. This is the ideal system. A boiler may also be used if there is a large area that requires heat.
2) A Dual Purpose System Without A Heat Exchanger: This is the least desirable system where the HWT provides hot water for hydronic heating and for household use. When the weather warms up the heating demands on the hot water tank are reduced or eliminated. This causes the water in the heating lines, radiators, and so on to become stagnant and can grow some fairly dangerous bacteria. These dual purpose systems without a heat exchanger should be set up to circulate the water through the heating lines several times per week to avoid problems. Fittings and supply lines throughout the heating system should be safe for use with potable water systems as you will be drinking this water. For example: if your heating system were running water through a lead radiator, that leaded water would be coming out of your kitchen tap at some point.
3) A Dual Purpose System WITH A Heat Exchanger: A heat exchanger is a simple device that allows heat to pass to the hydronic side of the system without the two water sources ever touching. This prevents cross contamination in these types of heating systems where the HWT is used for heating the space as well as the domestic hot water. The problem is they are rarely installed in the systems I see in Calgary.
Contact your local Plumbing and Heating specialist for all the pros and cons of each system as well as their capacity.