Boilers Part 12 – The Heating Cycle

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Let’s say you have a typical 3,000 square foot home with cast iron baseboard or radiators. This is what happens in a typical heating cycle.
Your thermostat is set at 70 Degrees Fahrenheit. The temperature in your home drops to 69 Deg. F. and your thermostat sends a signal to your boiler to fire. Your entire piping and radiator system is at room temperature or 69 Deg. F. Keep in mind that the weight of all your piping and radiators is around 5,000 lbs. Your boiler fires and starts warming the water, all the steel piping and cast iron radiators to 140 Deg. F. This will take around 20 minutes to achieve since there is 5,000 lbs to heat up. While your house waits for heat, the temperature continues to drop. By the time tha radiators warm up enough to start warming your home, the temperature probably has dropped to 65 Deg. F.
Now your 5,000 lbs of steel and cast iron has reached 140 degrees and the temperature has reached setpoint at 70 degrees. The boiler shuts off but the 5,000 lbs of steel in your home is still radiating het and the temperature in your home continues to rise. By the time your heat peaks and the radiators cool down and stop emitting heat, your home is probably 75 degrees.
Now your house starts to cool and the cycle starts all over again.
What is happening is that yu are getting a very wide range on 10 degrees in your home. This will not be comfortable and as you het your home to 75, you are wasting loads of energy.

In my next post I will illustrate the heating cycle with a DVCB (Direct Vent Condensing Boiler) that is equipped with Outdoor Reset.

For more technical details about reset, see this article from John Siegenthaler

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