re: Shop heating and cooling

I let my 7K/9K BTU propane heater run on high in the closed garage for a solid 2.5 hours this morning. I had a CO2 detector <10' away and a fan just to ensure homogeneous air yet it never registered over 0.0 ppm CO2 which I'm suspect of.  Previously I thought it was a 9K/12K BTU heater, upon further investigation, the original box set me straight.  That also helps explain the underwhelming performance with ~4T of metal starting at 42° trying to warm up to at least 50° while it's only 20° outside.