Hey all! I'm really struggling with this and any advice would be great.

I had a friend who has a pipe cutting and threading machine help me extend my natural gas line to the other side of my basement and into my attached 2-stall garage\workshop. I bought a used Dayton natural gas heater to put in the garage. It's a Dayton 3E402.

We got the gas line in place (1/2" the heater is 40k BTU) and the total length we ran from where it comes into the house is about 50 feet total. We have good pressure in the garage. We hooked the heater up, lit the pilot light and set the thermostat. As expected, you hear the valve open (Robertshaw 7200ER), gas runs for a bit, then the burners light. After the burners are lit for abut 2 minutes, the fan kicks on.

The issue is, it blows air that is barely warm. When I look at the flames coming out of the burners, they are only a couple inches high. I'm no HVAC guru at all, but they should extend a good 6 inches up into the heating element tubes right? I ran the heater for 2 hours and it barely increased the garage temperature by 5 degrees. (And it was rather warm today at high 30's)

What I've tried:

- Pull burners and make sure there were no clogs or other blockages
- Checked both orifices - no obstructions
- Pulled gas line off valve and checked screen, nothing restricting gas flow
- Tried adjusting pressure on valve, was already maxed out from previous owner
- Tried reducing pressure, flames even smaller
- Tried adjusting air allowed in burners - no adjustment gets the flames more than 2 inches high.

I'm thinking of replacing the valve with a new one, because this is an older heater and very simplistic and I'm not sure what else it could be.

Any ideas are welcome!

See pic...I have gotten a slid flame all the way across after adjusting the air intake on the burners, but the size of the flame stays the same!