Sunday, February 12, 2017

How To Build A Shop Heater Heat Exchanger

NOTE: PLEASE CHECK YOUR LOCAL REGULATIONS AS TO THE SUITABILITY OF A SETUP LIKE MINE

Difficulty Level (Easy, Medium, Hard, Insane):
Medium

Process:
For the last 5 or 6 years I've been using a direct heat diesel heater in my shop to heat it up in the winter. It works really well and even at -20 (celsius) it's up to a comfortable 20 degrees in about 5-10 minutes. Unfortunately, the exhaust fumes are also in the shop and after many years of breathing in those fumes I was actively on the look-out for an alternative.

I would like to mention, that I always turn on my air exchanger when the heater runs and  DO have a carbon monoxide alarm that I've had in my shop to make sure I don't accidentally kill myself, but even after a full day in the shop, it usually hovers around the 25 ppm range which, according to WHO, NIOSH and OSHA are all acceptable levels.

Once, I turned the air exchanger off, turned the heater on and left it on for 8 hours while I was NOT in the shop. After a full 8 hours of no air being exchanged, the CO levels were only up to 40 ppm but the fumes smelled awful.

In any case, I got the new heater on kijiji for $100 bucks (only so cheap because it wasn't working) and spent about a day Fixing the Indirect Diesel Shop Heater MH1000ID.

Once I got it running I called the local fire department to see what the code stipulated for these types of heaters because they're temporary by nature and the exhaust flue only gets to about 100 degrees (celsius) so it's not nearly as hot as a wood stove for example. I also consulted with a plumbing/heating friend of mine (thanks again for your time, Jordan!) and was confident to implement the venting.

Typically, these heaters are used outside and bring the hot air inside with a 16" hose, but I wanted to capitalize on the efficiency and have it stationed inside. The one thing that was still bothering me though is that I've had almost 3000 cubic feet of 200 degree (celsius) hot air per hour being vented outside which seemed like such a waste of heat, so after some planning, sketching and research decided to build an additional air exchanger to try to reduce the flue temperature even more.

A friend of mine has a CNC plasma cutter and since I've done some work for him on my lathe, he didn't mind cutting up the metal parts for me. I could have used the angle grinder instead, but cutting out the round and square holes would have taken a bit of time so the accuracy and convenience of the CNC plasma cutter was much appreciated (thanks, Eric!)

After cleaning up the pieces, I used my DIY Sheet Metal Brake to bend the pieces to shape, then drilled, sealed (with fire place caulking) and riveted the pieces together. All that was left, was to cut the existing horizontal flue with my angle grinder, install the newly built heat exchanger and put some high heat paint on it.

Now, the flue gases are already down to 150 degrees (celsius) and with an additional fan I should be able to get it down to around 100 degress which means I just cut the waste by 50%. Sounds like a successful project by any measure!

Files:
DWG: Heat Exchanger.dwg
DXF: Heat Exchanger.dxf

Videos:


 
Pictures:
The heater before the heat exchanger was installed
Energy savings calculations: $2/day


My inspiration: Very common in Europe
Some of my sketches
Some more sketches
The AutoCAD plans of all the parts


The parts and left over from the plasma cutting

The dirty metal parts

The cleaned metal parts

Measuring the flue gas temperature

Close-up of the K-type thermocouple
Running exactly 200 degrees (celsius)
Putting together the cap

Using fire place caulking to seal the cracks

Another view

Doing the channels

Sealing the channels to the plate

Another view
My setup

The rad/exchanger part done

Another view

Another view

Test-fitting the caps

Another view

Another view

Another view

Another view

The finished heat exchanger
The installed heat exchanger

Another view

Another view

Another view

The painted heat exchanger

Another view

Another view
Tools:
Metal band saw
Angle grinder
Belt sander
Hammer
Measuring tape
Digital calipers
Marker
Square
Level
DIY sheet metal brake
Eye & ear protection
Tin snips
Needle nose pliers
Rivet gun
Indirect diesel heater

Materials:
One 4' x 8' sheet of 22 gauge sheet metal
1/8" x 1/2" rivets
Two tubes of fire place caulking
One 6" duct starting collar
High heat paint

Cost:
$50

Time:
6 hours

Savings:
Not sure, maybe $100 bucks

Conclusion:
It works great and will save me a couple bucks in fuel per day

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