from Mary Ann in Pewaukee, WI :
#443
We currently have two 40 gal hot water heaters running parallel since we have a double whirlpool tub. This was suggested when we built our home 20 years ago. We would like to replace the two with one 75 gallon tank. Will there be an energy savings since we will only have one tank? This was suggested a few years ago during an energy audit.
Yes, this will save you money.
Changing out a 20 year old water heater, either with one unit or two, will save you money.
If the tanks were equal, a single tank would have less surface area than two tanks. Less surface area would reduce the amount of standby loss, and therefore save energy. The amount of savings will depend on the efficiency of the new water heater (compared to the old ones) and the type of fuel being used (gas or electric). Another option is to look into a water heater that has a higher first hour rating because of the efficiency and amount of gas used rather than the size of the tank.