Arcoliner tankless DHW coil sizing?

paulietools

I am hoping someone might be able to point me in the right direction. The tankless coil on our furnace blew out last night. I do mean literally blew a hole in the plate and had a stream of water shooting out the side of the boiler.

The system is an Arcoliner 0154T 1BT J2 rated @ 99 mbH for water and 1.35 GPH firing rate. The tankless heater has 589 cast into the plate but here's the issue. All of the plumbing houses I talk to want to know the GPM rating of the existing coil and tell me that it should be on the plate as a suffix to the 589. I have wire brushed the plate and there is nothing there.

How do I figure out the size so that I can order the right one? If it helps we have small cape with one full bath with tub, washer, dishwasher and kitchen sink. No other DHW outlets. I know the cold water flow from the well pump is approx 6 GPM but am afraid that a 5 GPM tankless will be too small.

FWIW one of the counter guys I talked to one very helpful but one was down right insulting. Basically said that I shouldn't be touching the system because I was not a licensed contractor and obviously didn't know anything because I was asking about the sizing. I may not be a heating contractor but I do work for Coen as a controls engineer designing burner management systems for industrial and power boilers. I think I have a pretty good grasp on how these things work.

billtwocase

should be

at least a 5 GPM coil. Is this worth it? As much as I respect and adore Arcoliners, this may be a task not worth doing

paulietools

Update

Thanks for the response. I went ahead and ordered the 5 GPM unit. It seems to work fine and fit was great. The coils don't seem to as robust as the original but then the original was made almost 60 years ago.

Unfortunately this was really the only choice I had to restore heat and hot water to the house quickly. I wasn't going to spring for a new boiler because of the possibility of selling the house in the near future.

I would have preferred to put in a tankless wall hung unit but we don't have natural gas in the neighbor hood and the house doesn't have a big enough electric service to handle an electric version.