Water Heater Thermostat
The water heater thermostat is set by the installing contractor to provide the required temperature at the hot water outlet of the water heater. It is important that a warning label be place near the water heater thermostat telling the homeowner not to change the thermostat setting. The label is included with the furnace.
Room Thermostat
The room thermostat controls both the water circulation pump and the air circulation fan. It should be on a centrally located, inside wall away from any source of heat such as diffusers, appliances and direct sunlight.
Energy Saving Room Thermostat
A set back thermostat or “smart stat” can be used with a combo system, but care must be taken in the timing of the temperature changes. The timing of morning warm up should be early enough that the desired air temperature has been reached before the people begin to use domestic hot water. The highest demand for space heating is during the morning warm up and the highest demand for domestic hot water is during morning showers. Even if the water heater is properly sized, it may not be able to meet this combined load. Therefore, large set backs should be avoided.
to achieve higher outputs from the furnace an
Hot Water Flow Rate
The hot water entering the water coil is the source of heat to the air handler. The effect of changing the amount of water entering the coil is the same as changing the water temperature. As water flow is reduced, the output of the air handler and the air temperature rise will both be lowered.
Air Handler Return Air Temperature
The return air temperature entering the air handler is approx. 60˚F (33˚C) below the hot water inlet temperature. If the return air temperature entering the air handler is reduced, more heat transfer will occur and the output of the air handler will increase.
Air Handler Air Flow Rate
The air entering the air handler can only be warmed by the temperature difference between the hot water and the cool air. As the volume (CFM (L/s)) of air is reduced, the amount of heat which can be transferred is also reduced.
Air Handler Output Capacity
There are four factors that will significantly affect the heating output of the air handler.
They are:
•Hot water supply temperature (EWT)
•Hot water flow rate (GPM)
•Air Handler return air temperature
•Air Handler air flow rate (CFM)
The hot water inlet temperature is typically 140˚F (60˚C). If this temperature must be increased
Air Handler Temperature Rise
In a fuel fired furnace, the combustion gases can be 1000˚F (538˚C) above the return air temperature. These units typically have a temperature rise from 50˚F (10˚C) to 90˚F (32˚C) and therefore delivers air at the diffuser at 120˚F (49˚C) to 160˚F (71˚C).
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