Gravity Vented vs. Power Vented - question

[YNOT2K]

i recently aquired a Reznor Model F gas heater. Reznor's website says that the Model F units are gravity vented. i notice that most folks on GJ are using Reznor Model UDAP, which Reznor says is power vented.
on Reznor's webiste https://www.rezspec.com/catalog-1__Unit_Heater.html it says that the Model F is not certified for residential use, and the UDAP is.
can someone explain the difference between the two venting systems and maybe explain why the Model F is not certified for residential use?
i had hoped to used this unit to heat my 3-car garage, using natural gas. do i need to sell this one and get a UDAP unit?

 

[dave67fd]

Without reviewing either one i can give you the basic differences between the two vent systems. If you have access to or can find the operators/installation manual you can probably find more specific reasons why one is certified residential and the other isin't.

Obviously, the "Gravity" vented means just that. It must remove its exhaust gases by natural convection, similar to a wood stove piping system.

The "Power" vented means the heater has an internal fan located at or near the flue opening which automatically turns on when the burner is lit. This "forces" the spent gases through the vent pipe.

The heater that is not certified for residential use probably has specific restrictions for venting and condensate line installation as well as having a gas pilot. The UDAP has direct spark ignition (no pilot) so that maybe the reason as well.

Again, if you have the ability to read the manual it should spell it out more clearly for you.