i have been getting ready to start my new engine lately and im about a day or so from it. it has been extremely cold lately her in ks and my garage heater has cracked along the side of the heat exchanger at least 6 in. long. would it be possible to weld a patch in to seal it up? i think it is aluminized steel, a new exchanger is $500 and i could buy a new heater for that. the heater is still working alright but im sure co2 is filling up the garage so i dont want to use it. any ideas?

If it cracked once I would think it would again, I would get a new heater.

Brian, don't even think about running the furnace with a cracked exchanger. I went through that and when I put a CO detector in (which I now believe is a must in a garage) I was surprised at how the levels can sneak up on you.

I believe that is why its called a "silent killer".

BTW I replaced mine with a Reznor and am exstatic at how efficient/quiet it is and how easy it was to install.
Here's how I got started:
http://www.chevelles.com/forums/showthread.php?t=213448

I also have a Reznor overhead natural gas, 65 or 75,000 btu's. I can't remember when I bought it for sure, maybe 1990, and I've never had to touch it, just turn the thermostat up and away she goes.:)

just received modine hot dawg 75 today. it will be installed tomorrow i looked at both brands and this one was cheaper than the reznor and still had a good waranty. its 15,000 btu bigger than old one and i insulated ceiling this week, so i should notice a big difference on gas bills. i hope