: I have a four year old, 40 gallon propane water heater and a 13 year old daughter (and 3 other kids). The tank is now under sized. Can another 40 gallon tank be hooked up with this one, if so how? or should I just go with a 75 gallon.
steve, yes you can use 2 40 gal heaters. set heaters side by side. come out of the cold on both heaters with a 6" brass nipple 90degree elbow, 6" nipple 90degree elbow, then a piece of copper, cpvc, or pex pipe.now you have the 2 cold water lines tied into the tanks together. now find the middle and put a tee on this line,before the tees you will need to put a 3/4" ball valve and union.after you put the tee in the middle tie in the cold water to this tee. do the same on the hot ,the tee must be in the middle of the heaters.putting a 3/4" ball valve and a union on the hot side allows you to isolate the heaters and change one and still have one going. use 5 x 3 x 3 wye on venting to tie in the 2 heaters.installing the heaters this way will get you the full use of both heaters.