The Joliet Bungalow was heated by a hot water system. Cast iron radiators were fed by an older natural gas, hot water boiler.  This boiler, believed to have been installed in the 1960’s, has an estimated capacity of 100,000 Btu/hr, with an estimated efficiency between 60 and 65 percent. The boiler was not operable at the time of the energy audit and could not be repaired.  Domestic hot water was provided by a conventional, natural gas, 40-gallon water heater with an estimated efficiency factor in the 50s.

To upgrade the energy efficiency of the Joliet Bungalow, the mechanical system was redesigned to include a unit that combines space heating with domestic water heating. The new condensing high-efficiency boiler has an AFUE (Annual Fuel Utilization Efficiency) of 92 percent. It comes with a very sophisticated control system. The system uses the thermostat in the space, but also has an outdoor reset control that reads the outside temperature and decides what water temperature should be circulated throughout the radiators. Flue gases are at such low temperatures that they are exhausted through the side wall, eliminating the need for a chimney.

Radiators were reconnected where necessary to provide even heating throughout the house.

Creating a system that combined space heating and water heating for domestic use made the old, inefficient hot water heater unnecessary, so it was removed.

Estimated Energy Savings

The annual energy savings for the boiler and domestic hot water upgrade is estimated to be 30 percent of the total energy used by the home. The system is estimated to save 525 therms of natural gas.  Electricity savings from the newer pump was not included in the estimate.

However, when all energy-saving measures are implemented together, the analysis shows an estimated annual energy savings of 41 percent (a combined 600 kWh and 701 therms). This translates into a net $54 electric and $764 natural gas savings, or a total of $818/year. 

The total savings is not the sum of all the individual measures because of interactions between the measures. For example, replacing incandescent lights with compact fluorescent lights saves electric energy, but because the compact fluorescent light gives off less heat, the heating bill increases somewhat. As the number of measures increase, these interactions become more complex.