View Full Version : Furnace Short Run Time
11-06-2006, 01:16 PM
I understand how my oversized system effects comfort in the summer when running AC but what about when using the furnace. It seems to me that even thought the system will satisfy the thermostat it does not run long enough to really heat ojects with any sort of mass to them. Floors, walls, furniture feels cold even though the room temp is 68 degrees. I also notice a blast of cold air when opening drawers and cabinates. Closets on outside walls also stay a lot cooler.
Not only is my system oversized but my house is also very tight further reducing the furnace run time. Do my comfort concerns seem to be a result of an oversized system or maybe something else?
11-06-2006, 01:49 PM
I don't think heating objects with mass, or cold air in cabinets or closets has anything to do with run time. A 70F house will eventually equalize all the objects in the room to be at 70F, regardless of run time. Spaces like closets next to exterior walls will stay cooler if the closet is left closed and does not have it's own supply register.
Now are you talking about cold rooms that have supply vents instead? That could indicate a problem with the distribution system that is made worse by the short run times. It's called air changes per hour and simply means that the system doesn't run long enough to mix all the air in all the rooms adequately, resulting in some hot and some cold rooms.
I can imagine you setback at times. If you are coming out of a setback, 68F will feel cold because the objects in the room are still absorbing heat because they aren't 68F yet. After coming out of a setback it is normal to have to overheat slightly until all the objects in the room equalize to the same temperature.
This is why I like the old manual thermostats (except for heatpumps). You turn it on when you are cold, you turn it off when you are hot, you are always comfortable. Who cares what the air temperature in one room next to the thermostat is?
11-06-2006, 02:46 PM
Yea I set the thermostat back to 66 while we are at work and then turn it up to between 68 and 70 when I get home. It takes a very short period of time to satisfy the thermostat but as I mentioned before things still feel cold. I understand your point that in time the temperature of the larger objects will equalize. Tonight I'll bring the temp up to 72 then cut back to 69 or 70 and see if that does the trick. This past Saturday morning my wife woke up freezing because I had it set on 66 while we were sleeping. She set it to 70 and the house was warm in less than 1/2 hour. She and the kids went out for the day while I worked around the house, so I set it back to 65 since I like it cold when I work. It took from around 9:30AM to about 1:30PM for the temperature to drop to 65 turning on the system even though it was below 55 outside. By this time everything in the house was cold again. I guess for comfort puposes it's best not to set it back so far during the day or at night. I burn propane however, and can feel the money being sucked out of my pocket while it's running.
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