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[FrozenMongrel]

I figured id put this here instead of in my boiler install thread because this isn't exclusive to a specific brand of boiler. U picked up an old miller mobile home downdraft furnace a few weeks ago from craigslist. It was a propane fired model, so I pulled all of the propane and related parts out. What I ended up with was basically a sheet metal case with a mounted squirrel cage fan. I measured the space I had at the blower outlet and ordered an appropriate water to air heat exchanger. Knowing that my barn is not insulated I used 2" thick foam insulation to completely line the area around the blower fan except on the intake side. That way when I'm not out there working I won't be wasting any heat.
When the heat exchanger was delivered I took some measurements and found out that the thickness was the same as the i.d. of some metal studs I had laying around. I took one and bent it into a U shape for the HX to slide into and riveted it together. After making a layout on the side of the furnace and cutting an appropriate sized slot, I put the U brake into the furnace housing and riveted it in place. The HX slid in very easily yet firmly enough that it isn't going to go anywhere. Because the downdraft model is supposed to be mounted on some sort of base, I pulled the front metal where the old propane burner used to sit and riveted it at an angle skating from the back to the front. I added another piece of foam insulation to that to keep as much heat coming out the front as possible. I'm going to cut a hole in the front of the door to fit as large a register grate as I can. For the wiring side of things I simply pulled out everything from the furnace and connected the fan wires to a 110v power cord through a light switch. Flip the switch on for the fan to kick in and have heat, and flip it off for no heat. I have the circulator pump at the boiler running 24/7 to function as a mixer for the G200. I'll probably add some sort of bypass plumbing and shutoff valves along with running a thermostat of some sort once the barn is insulated, but this was fast and cheap. Besides the Logstor pipe (28') my cost was a couple feet of 1" heater hose, 4 hose clamps, a little bit of copper and fittings to adapt the Logstor to 1"  copper, $50 for the furnace, $85 for the heat exchanger and some misc electrical supplies I had sitting around. About $15 more for the register cover and it'll be done. All in I have maybe 5 or 6 hours into the conversion.
The heat exchanger is rated at 96k btu's so we'll see how long it takes to get the barn comfortable next time I'm out working in it. No insulation and missing battens in a bunch of places will certainly not help, but way better than nothing. I put a thermal couple on my multi-meter and the air temp at the front of the furnace with the fan on was 111*



Just need to install the switch cover, tape up the heat exchanger to furnace seams, cut a hole in the door and put a grille of some kind on it.

[ijon]

Looks  like a good job to me. Simple and to the point.

[FrozenMongrel]

Looks  like a good job to me. Simple and to the point.

The design is from slimjim. He has a couple different mobile home furnaces he's converted this way. They work great and are inexpensive compared to a hanging unit heater.

[mlappin]

Of insulation, if I knew then what I know now, I would have saved my pennies or even borrowed the money to have our shop spray foamed instead of using the bubble insulation. The foil/bubble/foil stuff does work and is certainly better than nothing, but for air tight its hard to beat spray foam.

[juddspaintballs]

What you basically created was a quieter and cheaper version of a unit heater 

[FrozenMongrel]

What you basically created was a quieter and cheaper version of a unit heater 

And higher btu rating!

[mlappin]

What you basically created was a quieter and cheaper version of a unit heater 

And higher btu rating!

I like using old furnaces simply for the fact you can use air filters with em and keep the HX cleaner.

[hondaracer2oo4]

Nice job, looks good. I'm surprised you are only getting 111 degrees out of the front? My hydroair box puts out 125 degrees at the closest register which is about 15 feet from the coil and blower. My water also goes though a flat plate to get into the pressurized side of the system then goes to the water to air hx so I lose some degrees right off the bat there.

[FrozenMongrel]

Nice job, looks good. I'm surprised you are only getting 111 degrees out of the front? My hydroair box puts out 125 degrees at the closest register which is about 15 feet from the coil and blower. My water also goes though a flat plate to get into the pressurized side of the system then goes to the water to air hx so I lose some degrees right off the bat there.

I was using a cheap craftsman multimeter and hadn't let the furnace run long. We'll see the next time I run it how it performs. I was on my way out so I didn't have much time to evaluate it or let it run for more than a couple min.

[RSI]

The air temp going into the air handler can make a big difference on the output temp.

[hondaracer2oo4]

Intake air temp is a good point. If it is warming the air from 20-110 that is huge.

[FrozenMongrel]

Intake air temp is a good point. If it is warming the air from 20-110 that is huge.

It was 22* in the barn when I fired it up, so that would still be an 89* temp increase at a huge cfm.