My neighbor just tossed one of those heaters.
Scavenger that I am, I grabbed it from the curb and took it apart. Air pump was grenaded.
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So, I "invested" $20 between a pump and a filter kit. It took a few other tweaks. Like putting the burner can in an arbor press to square up the baffle. Lord knows how they pulled that out, but it works pretty good now.
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This one is a 70K BTU and it's been working okay, but the tank is not that clean and it tends to starve out and quit sometimes. Let it sit for a bit and it gets back to business for a bit until it repeats the performance. When the weather is a little warmer, I'll chase after cleaning it.
We also recovered a 155K BTU unit that had been abandoned at a job site. Really nice piece, but it will roast your biscuits if you're not keeping after it. Great for creating a baked enamel finish on things too.