I currently have an electric water heater that is nearing the end of its service life. I want to replace it with gas (there is gas and a flue located near the existing water heater - the WH is next to my gas boiler and there is a spare stub on the gas manifold) Here is my dilemma. The chimney is lined, with one thimble (for the boiler). The boiler enters the flue at 63" - too low for a standard water heater to tie in, and pushing the limit for a low boy (there would be about 6” of vertical before the 90 in order to keep a ¼” per foot slope). In addition, a low boy would fit the space, but it would totally block access to the water meter and shut off which is BEHIND the boiler in a corner. Right now I can reach around the current WH to get to the shut off, a low boy would be much wider (don't blame me, I didn't build the house). Now I could go with a power vent or condensing WH, but it would have to vent out through the garage, not from the laundry room where the WH is (the window and second story overhang means I can’t put the exhaust/intake out of the laundry room exterior wall). Or, I could go with an indirect water heater tank off of my boiler - but how will that be in the summer (my boiler is on the first floor of my split level house with no basement). Or, I could go with a tankless unit, making accessing the water meter in the future MUCH easier, but we still have the venting issue, and now I would have to determine if my gas service can handle the BTU demand of both a tankless and boiler firing at the same time. Of course if I punch a new hole in the chimney, insert a thimble, and add a tap to the liner, we could put in a standard height water heater - but adding that thimble is a job and a half.
I have no problem hiring someone to do the specific job - or heck, even doing it myself except for the indirect (I'm not plumbing and wiring in another zone myself) or punching a new thimble (my wife would kill me if I destroyed the chimney) - so any ideas? What sort of WH should I go with? This is a 4 BR, 2.5 bath house, with 3 girls plus my wife. We have a fairly high hot water demand. We need a high recovery system, and a pretty good tank size (if going with a tank unit)