In answer to the question above about who builds a dual- blower system...
We do. I designed the SplitSteam back in 2000 and demo'd it at our place in Marietta (Atlanta). It featured two over- driven #33- sized blowers and a 350,000 BTU propane burner.
It was tested at 195 CFM and 215 CFM for the Roots and Tuthill respectively, at 14 (or 15...?) inches Hg. and delivered 265 degrees with two wands running
simultaneously at 600 PSI with #6 jet size.
The current model features (2) #36 or (2) #45 blowers and the same heat...
IMO, it's not how much airflow a system moves "free air", but how much it moves through a wand. The free airflow is a valuable tool and definitely shows you if there's any inefficiency in the system itself. But once a wand is connected, everything changes. And you're simply not going to get 400 or even 300 CFM
through a wand.
No matter how "proven" a HX system is, it will always not be as much so as propane. Why? Because propane systems (as Les can attest to) have a head- start in our industry of some 20- plus years.
Propane is proven and "bug- free".
And, to get the kind of heat from a HX system you can get from propane (a continuous, high- flow 240 degrees, ATW), you'll easily be in the mid $20,000 range... for a single- wand system.
Dual wand... fugeddaboutit...
Aerotech or
Vortex pricing for that level of performance.