SRS, having worked for Heatilator, the manufacturer of fireplaces, I think what you have is not one of their products. Is this a rack for the fire made out of tubes, with air intake and fan at the bottom front, and which bend in a "C" shape so that the outtake is at the top, pointing toward the room? If so, I haven't seen those in quite a few years at the Hearth Products Association trade show. They worked well, except for that annoying little habit of burning out quickly.
If, however, you have a heat-circulating fireplace with a metal chimney, there is going to be a Rating Plate on it somewhere. This will give you the manufacturer, the model number, and the serial number. From there, the web is your best bet to find a customer service number, and it's downhill from there. If, however, you can't find it, call a local fireplace shop and pay for a service call. They can help you, or at least narrow down where to look. That's what we do.
Also, any fireplace insert sold in the US today meets the EPA limits on emmissions, and is exempt from local "No Burn" days, in MOST instances. A good EPA rated stove or insert burns clean, with no smoke after the intial lightup. Again, your local hearth shop can help.
On a different note:
Mountain Thyme, you're the reason that Hearth companies have to carry really good liability insurance. So far on this thread, you've recommended "two holes drilled through into the firebox", "a coil fashioned by you within the firebox", and blown off the risks of modifing a woodburning heater so that it has the potential to become a bomb in someone's home, or that there is no risk of the copper melting as long as you make sure you keep water in the system. Of course, if the tube DOES melt, has it occured to you that you now have several unplanned holes in the top of the firebox to emit heat, sparks, and smoke into the house? Also, the introduction of extra air can make a modern non-catalytic stove run extremely hot, also a fire hazard.
You also said: ""Heatalator" hasn't changed much in 40 years. The units still sell very well. Any good contractor supply has anything (new or replacment parts)you could need. The fireback is very thin for serious woodburning so a cast iron fireback is a good idea. The "smokeshelf" (flue control) is not at all a good design. Much smoke can be aleviated by modifying the draft for your purpose. The motor and squirrl cage are a standard product available from any good mill supply." Folks, if you follow any of this advice, you're stupid. Don't mean to be blunt, but stupid is the word. Let's review. By "Heatalator" hasn't changed much, you could be referring to one of two things. One is the actual brand name of Heatilator, which has changed their product massively over the last 40 years. Each one has gone through extensive UL testing, to ensure safety. If you meant the fireplace form, a metal shell which provides the shape of a firebox for a mason to build a masonry fireplace and chimney system around, those haven't changed much since 1927. But even they are UL tested. The fireback is plenty thick for "designed use". What the hell are YOU burning? Railroad ties? The flue control works fine, and again is tested. What modifications are you makeing? It's a damper, it opens and closes. And finally, motors and squirrel cages are usually heat rated for fireplace use, so they are not usually off the shelf parts.
Folks, please excuse my rant, but I've been in this industry a long time, and modifications to wood, gas, or pellet fireplaces, stoves, and inserts scare the hell out of me. When you modify a system, you do three things. 1. You void the manufacturer's warranty. You are now responsible for everything that happens to that system. 2. You void your home owner's insurance. If you burn your house down, and they discover that the fire was caused by a tampered with system, YOU ARE NO LONGER INSURED. 3. You risk burning down your home, and killing yourself and your family. I'm not kidding. There's a reason that my industry works so hard on safety. But if you bypass what we've done, it's your own fault.
So, please, contact a hearth shop, and deal with a professional. We care about your home and family, and we take great pride in what we do. Don't listen to an idiot who will write of the risks of modifications as "At this temperature point you would have a nasty bomb in you house!" Doesn't seem very worried, do he?