It can be ordered that way from Roberts-Gordon, but it won’t work that way.

The above cartoon is a 150-MBH heater with 40 linear feet of tubing and reflector.  We can order the additional tubing and reflector to make it 60 feet long.  It’s easy to do.

But before you do that, we need to let you know that the heat distribution out of these systems is not exactly uniform.  Below is a representation of what you can expect from any manufacturer of these heaters:

So when you specify additional tubing, you aren’t necessarily improving the heat distribution.

The additional tubing creates a bigger problem, though: the additional tube and reflector is really just exhaust venting.  So if we supply a heater this long, your installer suddenly has a lot less flexibility in venting it.  Here’s what we mean:

The below table is a summary of what you would find on page 47 of the 74-page installation manual with regard to venting the heater:

So back to our 150-MBH heater.  The manufacturer would count the 20 additional linear feet of heat exchanger as venting, so the contractor would need to provide combustion air and vent pipe lengths that do not exceed 45’ and two elbows combined.  If there is one horizontal or vertical offset required (two more elbows) then they only have 15 feet of venting to work with.  At that point, we likely have a project failure and back charges.

If you research other manufacturers, you’ll find different versions of the same problem.

So while you and your teammates may want to self-serve the selection of these heaters, we strongly encourage you to call your CFM Company sales representative and work through these details.

Some other possible solutions:

• Show a maximum number of elbows in your installation detail
• Specify heaters at their minimum length
• Specify manifolded negative pressure systems with a central pump
• Specify that the manufacturer supplies the vent tubing

We didn’t even cover the Category I and Category III vent types, but this article is already too long.  If you made it this far, thanks!