Reflow Oven Exhaust Temperature

Hi all.

We recently expanded our assembly space and moved our Heller 1500 oven to a new spot. In the old arrangement, we used a Purex filtration unit, keeping the hot air in our space. Recirculating the fumes caused a massive headache in cooling the facility in the hot Florida sun! This time, we have an 8in flex duct going to an 8in rigid, with two 800CFM exhaust fans in series going out the back wall. In our old location, there was a large mini-split AC unit that blew directly on the top of the oven and ductwork. The current location does not have that.

The issue is, no matter what airflow rate we have tried, the duct is incredibly hot. We are talking upwards of 70c when on a lead-free profile, and 60c when using leaded. Our fans are only rated to 60c max, so this is, of course, a big issue. Also, the oven gets warm to the touch - maybe like 30-35c. Not sure if any of this is normal since again, our old space had an AC directly over it.

The heater outputs stay at around 10% - 30% tops. On the low end, we are at ~200CFM on the hot end exhaust, and 1XX CFM on the front exhaust. Full speed adds another 150CFM to each. We can't lower the speed without actually baffling the intake to the oven. We have a baffle installed, just not sure if that's the right approach.

Ideally, I would like to use some heavy insulation wrap on the entire ductwork, to reduce the amount of heat that goes to our space from the ductwork. But, of course, with the fan rating issue, this isn't an option, as it would worsen the temperature.

Any advice or suggestions? Or is this common? The options that I see are:

1) Add a few holes in the exhaust near the oven, allowing the intake of cold air to mix with the hot air inside.

2) Try lowering the CFM of the exhaust, reducing the oven output.

3) Using some fans to cool the ductwork. I hate this approach since it just moves to heat back to our space.

4) Use a high-temperature fan, and just ignore any of the temperature issues. If this is the case, please recommend a fan - I have searched everywhere for one, they all seem to be rated at 60c-70c.

Thanks! Kyle

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