There's been a little discussion recently about the pros and cons (mostly cons) of draft blowers. Supposedly they cause your warm air-forced draft furnace to eat Mount Everest size piles of firewood in just a few short minutes. I made a couple of simple adjustments to my DAKA that made a monster difference in performance and the amount of firewood it consumes. I'm assuming most any forced draft blower type furnace is controlled in a similar fashion... by a Honeywell combination fan/limit controller.
This controller starts/stops the circulation blower and "limits" the draft induction blower. When you pop the cover off you'll find three adjustable tabs on the dial... you can move them with your finger but it's easier to use a small screw driver or pick (be sure to hold the dial in place with your other hand so the biometric spring ain't damaged). From the factory it comes set to turn the circulation blower on at something 'round 110-115°, and turn it off at 'round 90°. The third tab is the draft induction blower limit... the factory setting is 200°. What this does is turn the draft induction blower off if air jacket temperature reaches 200° for safety reasons (it turns it back on when air jacket temps fall to approximately 160°). This is approximately what the "factory" settings will look like...
There's a huge problem with these settings... they ain't really done with a wood-fired appliance in mind, they're set with gas or oil furnaces in mind. Understand, this thing is sensing air temperature, not firebox temperature, and most of the time it's sensing that air temp while the circulation blower is pumping cool air into the jacket. And, unlike a gas/oil furnace, it ain't mounted above the heat exchanger, it's mounted off to the side of the firebox.
First of all, the "Circulation Blower ON/OFF" settings are too low. There's no reason for the blower to come on that early (110°) and start cooling a firebox that ain't even hot yet. Also, the "ON/OFF" is too close together... which will cause the circulation blower to short-cycle (especially at such low temps). B'sides, with the two of them set so low the air coming from your heat vents feels cool... meaning you'll feel a cold draft. Performance will be improved if both settings are raised and the separation between them is increased.
Second, the "Draft Induction Blower LIMIT" is too high. Now remember, it's reading air jacket temp off to the side, not air temp above the heat exchanger... and there's cool air being pumped into that air jacket by the circulation blower. So, unless you have that smoke dragon furnace stuffed to the gills with oak it ain't never gonna' hit the "LIMIT"... meaning the draft blower runs continuously, and that's gonna' eat a ton of wood without any real benefit. Better if the draft blower cycles on and off... runs for a few minutes, shuts down until the heat is circulated into the home and the jacket begins to cool before starting up again. In other words, lowering the "LIMIT" (so the draft blower cycles) will put less heat up the chimney and more in the home... i.e., heating efficiency is increased (increased a ton).
Now there's a mechanical limit to the adjustments because of how the tabs are set up. The minimum temperature difference between the "Circulation Blower ON/OFF" settings is 20° (which is too close anyway), and minimum temperature difference between the "Circulation Blower ON" and the "Draft Blower LIMIT" is 30°. I set my "LIMIT" down to 175°, and my "ON/OFF" up to 145° and 110° respectively... both of them higher, and with a 35° temperature difference instead of 20°.
My firebox runs hotter in "stand-by", meaning more efficient combustion (i.e., little if any smoldering). The circulation blower cycles on and off less often, especially during the beginning and end of a burn cycle. I never get the "cool" feeling air from the heat vents. And most importantly, the draft blower cycles on and off when the thermostat is calling for heat (i.e., way, way, way less fuel consumption)... and believe me, even at the 175° "LIMIT" the air coming from the heat vents is friggin' hot‼ You may need to experiment a bit for the settings that work best with your setup... but I'm bettin' they won't be far from mine.
I added one more little thing to my furnace. A cheap snap switch in-line to the wall thermostat that comes on (closes) at 110° and goes off (opens) at 90°. Basically what that does is cut the thermostat power when air jacket temperature drops below 90° (20° below the circulation blower "OFF" temperature)... in other words, the draft blower won't run on a cold, dead firebox.
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This controller starts/stops the circulation blower and "limits" the draft induction blower. When you pop the cover off you'll find three adjustable tabs on the dial... you can move them with your finger but it's easier to use a small screw driver or pick (be sure to hold the dial in place with your other hand so the biometric spring ain't damaged). From the factory it comes set to turn the circulation blower on at something 'round 110-115°, and turn it off at 'round 90°. The third tab is the draft induction blower limit... the factory setting is 200°. What this does is turn the draft induction blower off if air jacket temperature reaches 200° for safety reasons (it turns it back on when air jacket temps fall to approximately 160°). This is approximately what the "factory" settings will look like...
There's a huge problem with these settings... they ain't really done with a wood-fired appliance in mind, they're set with gas or oil furnaces in mind. Understand, this thing is sensing air temperature, not firebox temperature, and most of the time it's sensing that air temp while the circulation blower is pumping cool air into the jacket. And, unlike a gas/oil furnace, it ain't mounted above the heat exchanger, it's mounted off to the side of the firebox.
First of all, the "Circulation Blower ON/OFF" settings are too low. There's no reason for the blower to come on that early (110°) and start cooling a firebox that ain't even hot yet. Also, the "ON/OFF" is too close together... which will cause the circulation blower to short-cycle (especially at such low temps). B'sides, with the two of them set so low the air coming from your heat vents feels cool... meaning you'll feel a cold draft. Performance will be improved if both settings are raised and the separation between them is increased.
Second, the "Draft Induction Blower LIMIT" is too high. Now remember, it's reading air jacket temp off to the side, not air temp above the heat exchanger... and there's cool air being pumped into that air jacket by the circulation blower. So, unless you have that smoke dragon furnace stuffed to the gills with oak it ain't never gonna' hit the "LIMIT"... meaning the draft blower runs continuously, and that's gonna' eat a ton of wood without any real benefit. Better if the draft blower cycles on and off... runs for a few minutes, shuts down until the heat is circulated into the home and the jacket begins to cool before starting up again. In other words, lowering the "LIMIT" (so the draft blower cycles) will put less heat up the chimney and more in the home... i.e., heating efficiency is increased (increased a ton).
Now there's a mechanical limit to the adjustments because of how the tabs are set up. The minimum temperature difference between the "Circulation Blower ON/OFF" settings is 20° (which is too close anyway), and minimum temperature difference between the "Circulation Blower ON" and the "Draft Blower LIMIT" is 30°. I set my "LIMIT" down to 175°, and my "ON/OFF" up to 145° and 110° respectively... both of them higher, and with a 35° temperature difference instead of 20°.
My firebox runs hotter in "stand-by", meaning more efficient combustion (i.e., little if any smoldering). The circulation blower cycles on and off less often, especially during the beginning and end of a burn cycle. I never get the "cool" feeling air from the heat vents. And most importantly, the draft blower cycles on and off when the thermostat is calling for heat (i.e., way, way, way less fuel consumption)... and believe me, even at the 175° "LIMIT" the air coming from the heat vents is friggin' hot‼ You may need to experiment a bit for the settings that work best with your setup... but I'm bettin' they won't be far from mine.
I added one more little thing to my furnace. A cheap snap switch in-line to the wall thermostat that comes on (closes) at 110° and goes off (opens) at 90°. Basically what that does is cut the thermostat power when air jacket temperature drops below 90° (20° below the circulation blower "OFF" temperature)... in other words, the draft blower won't run on a cold, dead firebox.
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