If you have a power vent, then there was some issue that would not allow you to vent straight up through the roof. Other than relocating the water heaters to a location that would offer venting straight up, or if your climate permits, switching to a tankless on the exterior wall where it's currently located, there isn't any other real solution. Both solutions would be pretty costly, especially as you have two water heaters.

Shelf life on a hot water heater is 15-20 years so yours has had a good life It would be cost effective to replace it. That said it sounds like you may have sediment in your lines that is slowing things down. I would venture to guess the bathroom with the most hot water is/was the one least used. So that would lead I am sure to how to fix it and that would depend on many thing like the age of your plumbing and what kind of pipes they are. There are a few things you might be able to have a plumber do but not many so your water lines may need replaced also. If you got a home owners warranty when you bought your home it may cover both the tank and any water line replacement Good luck Amy

THANK YOU so much for your responses. Jake: I totally forgot about the fact that we need to update/upgrade our electric panel for our 1976-house. So any electric option is not viable. asolo: I read a couple of your other posts about tankless; I'm very convinced not to do tankless. joeplumb: our furnace (boiler) is designed to heat up the 1st floor, 2nd floor, and an indirect water heater. so to get a direct water, we'd wouldn't be utilizing our furnace optimally. We're in MA: very high gas and oil and electric prices. And forecasted to be worst this winter. sigh. We went with the SuperStor indirect stainless steel water heater, which is supposed to work great w/ well water. Yay for hot showers again. again, thank you very much.

I have exactly the same problem. I have no idea how the air gets into my hot water lines . I recenlty installed a new hot water tank and its a simple one for one.I never had this problem before but now each morning I have nasty burps at the faucet I first use . Its great for the rest of the day but only in the morning do I get the trapped sputtering air. I do have an existing Vacuum relief valve attached to the cold intake line to the Hot water tank and itys probably 25 to 30 years old there is no leakage but could this somehow be allowing air into my hot water tank.? I am also scratching my head.