PSG Caddy please help!

[NH_burner]

What kind of filter(s) do you have in? If you go to a higher MERV filter that will lower the CFM output some too...

I just put in two filtrete filters, I believe they are 1500 MERV. I thought about increasing the MERV, and for the sake of throwing ideas around, I thought about the idea of stacking up filters to increase resistance but I can't imagine that being good for the blower. Choking the return side to address a supply line issue feels like cheating and masking the problem and I'm wondering if that may be bad for the blower? Not only that, but the high pressure is indicative of a low flowing system. If I do manage to substantially reduce my pressure I may be getting little to no flow of air coming out of my vents.

So supply duct is 160 sq inches (probably a bit on the small side) and then that goes into flex line?
Return line is 154 sq inches...which should actually be at least 10% bigger than the supply.

Correct, but since the supply line is being bottlenecked by the 6" flex ducts, I'm guessing this set up resembles a system where the return is 25-50% larger than the supply. If I replace some of the flex with rigid duct then I may get to a point where the return air needs to be addressed.

 

[NH_burner]

Problem solved So over the weekend I bought a 6x10 grill to put directly into the supply trunk to reduce my static pressure. Surprisingly, cutting a large hole, even before I put the register in, did not reduce my static pressure! This got me thinking about changing the supply plenum to make a more gradual transition from the 2'x2' (I'm guesstimating the size) plenum down to an 8"x20" trunk, but that won't be necessary as I now know.

The supply trunk has two normally open, electrically closed dampers in it. One to block the gas furnace when heating with the wood, and one to block the wood furnace when heating with the gas. Before actually wiring them in, my HVAC guy changed his mind and decided to go with the simplicity of mechanical backdraft dampers. I agreed that this would be simpler and provide better controls. The reason for needing any damper is prevent short cycling the air through the unused furnace. What I did not realize, is that he put in an additional damper to block the wood furnace when it is A/C season. I looked up at the right spot to see a handwritten "HEAT" and "A/C" with the damper pointing at the "A/C". smh. This whole time the wood furnace was trying to push air through the damper. Surprisingly, it was still heating the house, just with very little efficiency.

So my static pressure went from around 0.62-0.63 to about 0.15. I increased the fan speed to medium and now I'm right at 0.2. What a difference Both with how the fire burns and how easily the house is heated. I love seeing that secondary burn kick in. This weekend the house went from 66 to 72 in what seemed like 30 minutes. Can't complain about that.

My chimney temp is usually around 200, but does get close to 300 with a large hot fire. Seems kind of cool - is that usual?

 

[sloeffle]

My chimney temp is usually around 200, but does get close to 300 with a large hot fire. Seems kind of cool - is that usual?

I'm glad you solved your problem. Wire up a timer, and a speed controller and you'll like your furnace even more.

I have a temp probe about 6 - 10 inches from the back of my furnace. I shoot for temps between 300 - 400F depending on where I am at in the burn and how much wood I've put in.

 

[JRHAWK9]

This whole time the wood furnace was trying to push air through the damper.

yeah, that would explain it!!

My chimney temp is usually around 200, but does get close to 300 with a large hot fire. Seems kind of cool - is that usual?

External temp on single wall stove pipe or internal flue gas temp? If it's the external pipe temp (usually taken by an infrared gun), this is not an accurate temperature. Internal flue gas temps are much higher....like twice that of the external pipe temp.

 

[NH_burner]

External temp on single wall stove pipe or internal flue gas temp?

It's double wall stove pipe and internal temp. I'm using a thermometer with a probe on it. Wood I'm burning is green, and probe is probably about 18" from back of furnace

 

[NH_burner]

I'm glad you solved your problem. Wire up a timer, and a speed controller and you'll like your furnace even more.

I'm assuming the timer is to keep primary air open after loading, even if thermostat isn't calling for heat?

And speed controller is to make the blower continuously variable based on plenum temp.?

 

[brenndatomu]

So my static pressure went from around 0.62-0.63 to about 0.15. I increased the fan speed to medium and now I'm right at 0.2.

Sounds much better...now, don't get too hung up on hitting .2" SP...go ahead and try it like you have it, but then go back to low speed, try it like that too...I bet you end up sticking with low speed.
I don't even try to hit .2 anymore...especially if you put a speed controller on it...99% of the time the blower will not be running at full speed anyways.

I'm assuming the timer is to keep primary air open after loading, even if thermostat isn't calling for heat?

And speed controller is to make the blower continuously variable based on plenum temp.?

Yes. Any if you install a temp controller (fairly easy and cheap to do) along with the timer it will turn your furnace into a "load and go" machine! Almost as easy as a Kuuma! Plus it gives you protection from "over-firing" also.
And yes on the speed controller question too.

 

[JRHAWK9]

My chimney temp is usually around 200, but does get close to 300 with a large hot fire. Seems kind of cool - is that usual?

It's double wall stove pipe and internal temp. I'm using a thermometer with a probe on it. Wood I'm burning is green, and probe is probably about 18" from back of furnace

My guess, with those low temps, you are possibly taking the temp reading in a part of the pipe which does not represent the actual max flue temp. Assuming it's being metered BEFORE the BD is mixing in basement air. The placement of the probe as well as how far the probe extends into the pipe does make a difference. Of course, the instrument you are using could be off too. I would expect your flue temps to be more like 300°-500°. Less when the damper is shut and more when it's open.

 

[Highbeam]

As the common condar flue temperature probe will tell you, flue gas temps under 400 are too cool. Over 900 is too hot.

The problem with such low flue temperatures is that the inevitable water in the flue gasses will condense and create creosote.

 

[NH_burner]

As the common condar flue temperature probe will tell you, flue gas temps under 400 are too cool. Over 900 is too hot.

The problem with such low flue temperatures is that the inevitable water in the flue gasses will condense and create creosote.

Understood, but I thought that the gasifiers intend to operate with colder flues because there is no smoke to create creosote.

My guess, with those low temps, you are possibly taking the temp reading in a part of the pipe which does not represent the actual max flue temp. Assuming it's being metered BEFORE the BD is mixing in basement air. The placement of the probe as well as how far the probe extends into the pipe does make a difference. Of course, the instrument you are using could be off too. I would expect your flue temps to be more like 300°-500°. Less when the damper is shut and more when it's open.

MY thermometer is just a few inches before the BD, too close? It has a 4" probe and it's in 6" double wall (actual OD is 7") so it should be reading 1/2" from dead center.

 

[NH_burner]

Yes. Any if you install a temp controller (fairly easy and cheap to do) along with the timer it will turn your furnace into a "load and go" machine! Almost as easy as a Kuuma! Plus it gives you protection from "over-firing" also.
And yes on the speed controller question too.

Is there already a thread out there covering these mods? I can't seem to find one in a quick search.

 

[brenndatomu]

Understood, but I thought that the gasifiers intend to operate with colder flues because there is no smoke to create creosote.



MY thermometer is just a few inches before the BD, too close? It has a 4" probe and it's in 6" double wall (actual OD is 7") so it should be reading 1/2" from dead center.

Caddy isn't really a gasifier.
Yeah that sounds too close to the BD...and as someone else mentioned, probe insertion depth/location can make a big difference...might want to experiment with that.

Is there already a thread out there covering these mods? I can't seem to find one in a quick search.

Not specifically...click the link in my sig line...that will take you to an index of sorts for the Everything Tundra thread...that would be about the best place I can think of...and it will still take some digging...

 

[NH_burner]

Not specifically...click the link in my sig line...that will take you to an index of sorts for the Everything Tundra thread...that would be about the best place I can think of...and it will still take some digging...

Thanks! Wasn't too difficult to find.

 

[Highbeam]

Understood, but I thought that the gasifiers intend to operate with colder flues because there is no smoke to create creosote.

Essentially, all wood burning is done via gasification. Some appliances burn the gas fuel more thoroughly than others but none are 100% effective at eliminating creosote and especially not a wood furnace like your caddy that is really just a woodstove with a big blower and a heat stripper in the flue path.

You need standard flue temperatures to power the draft and to keep the water from condensing. There is always water. Lots of water. You want that water to leave the chimney cap as vapor which means that you need to assure a warm enough flue gas temperature.

 

[NH_burner]

Here's where my thermo is...

 

[brenndatomu]

Have you checked its accuracy? They can be way off...stick it in water when it just starts to boil...

 

[NH_burner]

Have you checked its accuracy? They can be way off...stick it in water when it just starts to boil...

No I haven't, just assumed a new product would work as it's supposed to. I'll have to check it I guess.

 

[NH_burner]

I'm thinking about doing the mods and just hoping you guys can confirm that I'm understanding how this thing operates correctly...

My thermostat for fan control is currently set at 110, 150, 250. The fan control box has four speeds and two of them are used and selected by hardwiring a red and black wire to those speeds. At 150, the fan comes on at the higher of the two speeds, then goes off at 110. The lower of the two fan speeds is only used for the "summer switch" in which the fan is turned on manually? So the high limit of 250 doesn't do anything to change the fan speed it only opens the circuit causing the primary air damper to close?

 

[Highbeam]

Have you checked its accuracy? They can be way off...stick it in water when it just starts to boil...

well of course it’s off if you test it like that! The meter is designed and calibrated to be installed in double wall stove pipe with the bimetallic spring out in ambient air. Your only hopes of testing it are with a second identical meter or with a thermocouple properly inserted into the exhaust stream.

just like those people putting stove top meters in an oven and expecting to verify accuracy that way. That’s also wrong.

 

[brenndatomu]

well of course it’s off if you test it like that!

Hmm...yeah, good point...I wasn't thinking about that being a bi-metallic spring thermometer...oops

 

[brenndatomu]

My thermostat for fan control is currently set at 110, 150, 250. The fan control box has four speeds and two of them are used and selected by hardwiring a red and black wire to those speeds. At 150, the fan comes on at the higher of the two speeds, then goes off at 110. The lower of the two fan speeds is only used for the "summer switch" in which the fan is turned on manually? So the high limit of 250 doesn't do anything to change the fan speed it only opens the circuit causing the primary air damper to close?

Sounds to me like you are understanding correctly...maybe @laynes69 or @sloeffle could confirm?

 

[sloeffle]

I'm thinking about doing the mods and just hoping you guys can confirm that I'm understanding how this thing operates correctly...
My thermostat for fan control is currently set at 110, 150, 250. The fan control box has four speeds and two of them are used and selected by hardwiring a red and black wire to those speeds. At 150, the fan comes on at the higher of the two speeds, then goes off at 110. The lower of the two fan speeds is only used for the "summer switch" in which the fan is turned on manually? So the high limit of 250 doesn't do anything to change the fan speed it only opens the circuit causing the primary air damper to close?

My furnace has a "summer switch" too. I have it wired into the lowest speed like you do. Before I got my speed controller I would wait for the second fan speed to come on and then turn the "summer switch" on. This would help with the off and on fan cycling at the end of the burn.

Yep, that is your high limit. When the temp hits 250 it essentially cuts power to the 12v transformer. It is there to keep from over firing the stove.I keep mine a little lower but it is all personal preference.

 

[NH_burner]

Sorry I've been away for a couple days, but I wanted to thank everyone for all the help!