Thermal Corp SF-85 heat exchanger ratings

SCB Inc

I've been called in to evaluate an obviously undersized heating system. I need to find out how many btu's/hr an old (30yrs?) Thermal Corp SF-85 heat exchanger will produce at a given temp. The company is or was from Ozone Park New York Ive looked up the name on the internet but its licensed to an electronics Co. Ive called all local heating suppliers with no success.