Gas Water Heaters (for heat)

In the last few years a new system has been introduced that uses a modified gas hot water heater to heat the potable water and heat the air in the house. In these systems, hot water from the tank is circulated through radiators in the individuals rooms or in a duct system.

These systems are being used in smaller units such as smaller townhouses and those that are well insulated and thus require less heating capacity. The advantage of these systems appears to be primarily in their lower up front cost.

How satisfactory are these systems? I don't know. My guess is that they will work well in moderate climates and small families. I am less sure about the adequacy of these systems during very cold periods or in homes that use a lot of hot water.

Imagine the following scenario: During a cold snap, a family of 4 takes four long showers during a 2 hour period. At the same time, a washing machine is also used. Under normal circumstances such hot water usage would tax the capacity of a 50 gallon gas water heater - pity the poor person who takes the last shower. In this case, the lack of hot water would also delay the heating of the house. It might take 45 minutes to heat enough hot water to heat the interior of the house.

One nice feature that I have seen in some homes with such heating systems is the use of a gas fireplace/area furnace as the primary or auxiliary heating source in the living room. Ideally such a gas fireplace would be on a thermostat and be an adequate area heating source. If the living room is also on the main floor, then such a fireplace can provide some heat to other portions of the house through natural convection.

Article: 
Heating Your Home