Answer: -my girlfriend had 2 they were in series -I don't quite get what your saying hewre but if your talking about have a 50 gal. water piped to the bath rooms and kitchen and then want a 20 or 30 gal. put at the bath room say under the sink to have 30 gal. right there and then have the 50 gal. to pick up where the 30 leaves off. Yes, I have seen this on a few jobs and it works pretty well. I see this on jobs where they have large tubes or those spa type tubes and need large amounts of hot water to fill them. 80 Gal. of hot water will fill a good size spa or tub then figure in about 30 more gal. of cold water make about 110 gal. to fill the tub's and spa's. . -Yes, I've seen two water heaters in series before. It is very possible. Works nicely.