I'm replaceing and 40+yr old Williamson forced hot air furnace 140kBTU/ 3.5 ton and Ford 30 gal water heater. both vent into a 20' Amerivent 7'' factory built double wall SS chimney ( see pic ). I have ask two small time Plumbing & Heating contractors in my area if its possible install a Toyotomi OM-148 ( Listed as a forced flue system ) on demand tankless water heater and a Carrier Performance 80 variable speed oil furnace and reuse the existing 7"chimney.
Toyotomi OM-148 has a 2.5" flue and comes with an optional 5" adapter for use with chimney's. The Carrier furnace has a 6" flue. a local sheet metal guy said he could make a Galv 7" wye pipe with a 5" 45 degree to put the Toyo 5" pipe above the 6" furnace pipe and replace the existing 6" to 7" T as seen in the picture.
I have not heard back from either guy. my suspision is they cant determine if venting will be an isuue or they are uncomfortable with the Toyo OM-148 WH. Has anyone ever done an install like this or have any venting experience with the Toyo. Direct venting the unit is not an option where it will be positioned.
Thanks, For any and all Help.