Posted By Jelly on 04/07/2009 10:12 AM
Yeah, the AC is needed for the majority of the year in these parts. But there are about 4 months of the year on the other hand, when the heat pump would be on call for forced air heat. During those months would it make more sense to just switch the hot water heater tank back over to resistance? Or would letting the heat pump do double duty actually increase the efficiency?
Finding a pro to do the math is what I'm worried about.
Letting the heat pump do double duty for both space & water heating is the right thing to do- it increases the duty-cycle of the heat pump, which increases it's average operating efficiency as long as it isn't short-cycling. Randomly timed 3 minute cycles would make it less efficient- 10 minutes + is better. But as long as it's over 25F out, even short-cycling it may still be more efficient than heating your HW with resistance heating. The short cycles would cause the seasonal operating efficiency of the heat pump top be much lower than it's steady-state operating efficiency, but overall you'd still use less electricity than if you went with all-resistance electric hot water heating.