Need help with an internal exhaust problem

Need help with an internal exhaust problem

PostBy: Halleys5 On: Mon Jan 21, 2013 1:26 pm

I'm hoping one of you might be able to help me out with a problem I'm having with a Reading Juniata stove.

Bought this stove used and did a bunch of work on it. Regasket, full-time combustion air, outside combustion air, baro, mano, Power-Vent.

The problem is that at a mid-burn, the flue stack will get close to 300 degrees while my convection air hovers around 100.
I have an Alaska stove upstairs and the stack never gets that hot. It also sips coal (a bag a day if I push it), while the Juniata gulps it down.

The internal workings of the exhaust are pretty simplistic which I think is the problem. There is just a single sheet metal baffle that the exhaust flows around on its way out of the stove. I'm thinking about adding some complexity to the exhaust path to try to get more heat up into the exchanger before it vents out.

In this rudimentary drawing, the plate I am talking about is the green line in the cross section view. The second drawing is a plan view of that same plate and the blue line represents what I'm thinking about doing to it by adding some flat steel standing on edge in the pattern shown.

There is a concern about restricting the flow too much, but even with my baro set all the way down to 0.02 AND ADDING a washer to the weight, my manometer still reads 0.04" measured a couple inches up the stack from the top of the stove. So I think I have room to work.

I thought about maybe taking some pieces of broken fire brick and trying to just close off some of the front opening over the plate for starters to see how that helps.

I'm looking for advice here.... ;) I can't see how running twice as much coal for half as much heat leaves me any better off than I was when I just had my trusty Alaska heating the main part of our house.
Thanks in advance!!

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Halleys5
 
Hot Air Coal Stoker Furnace: Reading Juanita
Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing II

Re: Need help with an internal exhaust problem

PostBy: Rob R. On: Mon Jan 21, 2013 1:31 pm

It sounds like the speed of your power vent needs to be reduced via a rheostat. What is the draft supposed to be for this particular stove?

Are you using the minimum amount of combustion air required to get a proper burn?
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Need help with an internal exhaust problem

PostBy: Halleys5 On: Mon Jan 21, 2013 3:46 pm

I've got my power-venter running almost at the minimum on the rheostat. The baro is set so that there is nearly no movement in my manometer when the power-vent is set full tilt or near minimum. But the manometer does jump if I move the baro damper open or closed just a bit, so I know my manometer is working.

I don't know what the suggested draft is, that is a great question.... Just looked it up and it says 0.04-0.06 (doesn't say where it should be measured from), I'm running 0.04 at the base of the stack.

As for the combustion air, I am using a 50 cfm (free air cfm) Dayton 1TDN7 blower. The burn looks very good. More flame than my non-converted tri-stoker but the ash isn't flying off the grate either.

Great questions, thanks for asking. Maybe this give you a clue as to where I can go next.
Halleys5
 
Hot Air Coal Stoker Furnace: Reading Juanita
Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing II


Re: Need help with an internal exhaust problem

PostBy: Lightning On: Mon Jan 21, 2013 7:27 pm

Seems like there is too much air going thru the firebox carrying heat out the chimney..
Can you reduce the combustion blower setting? :?
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Need help with an internal exhaust problem

PostBy: WNY On: Mon Jan 21, 2013 7:32 pm

The baro can be open which reduces the draft on the stove, where exactly are you measuring the Draft?

It sounds like something is not calibrated correctly on your baro or power vent and sucking too much draft out of the stove.

Which Baro Damper are you using? Maybe post a pic of your setup.

Typcially .04 is good for most stoves.
WNY
 
Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

Re: Need help with an internal exhaust problem

PostBy: Halleys5 On: Mon Jan 21, 2013 10:51 pm

Thanks for the continued investigation.
I hadn't considered the possibility that the combustion fan is cranking too much. I wish there was an easy way to measure airflow. I figured that with 50 cfm free air, with my inefficient airflow and 5 feet of 4" pipe to the outside, I would not be getting more than 40+/- . I think most tri-burners operate at 35ish from the factory. I will have to experiment with that. The blower does have a restricter plate on it but I have it wide open and non-adjustable at the moment. But I'll figure something out.

I'm measuring draft about 2" up from the stove flue collar (which is on the top of the stove with the Juniata).

I'm using the standard Field Controls baro that came with the LL Power-Vent, model RC. I thought it was strange to have such a discrepancy between my manometer and the baro. on my Alaska stove with the identical set up the baro is set at 0.04 and that is where the mano reads. Now that you mention it that has me a little concerned/curious.

Here's some picts, please overlook the phone-camera and the temporary electric (I'm a work in progress :oops: )
The burn setting in pict two is what I am calling a medium burn. Sure looks nice in person, skinny burn line with higher flame than my other tri-burner.
You probably can't make out the pict of the combustion blower, but it is mounted with the discharge blowing at 90 degrees from the airflow direction into the firebox. So the air coming in is making a hard turn right out of the blower. I'll try to take a shot with a real camera too.

Thanks! For the continued help!! :D
Sorry for the rotated photos, phone-camera-internet-old fart-conflict.


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Halleys5
 
Hot Air Coal Stoker Furnace: Reading Juanita
Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing II

Re: Need help with an internal exhaust problem

PostBy: Halleys5 On: Wed Jan 23, 2013 11:07 am

Here's a couple better pictures.
I put a small fan on the flue like I read on another thread and that does reduce the pipe temp substantially. I assume I'm still flushing a lot of wasted heat up the stack though. The first picture shows my combustion blower setup. Its a 50 cfm blower and you can see the hard angle it is discharging into. Also below is a picture of the burn. It looks reasonable to me, tell me what you think. I've only ever seen my two stoves in action so I don't have much to compare to.

The second picture below is the "Great Wall of Juniata" that I have built out of pieces of rock paver to try to alter the exhaust path and get more heat out of the gases. I can't say that its working but the exhaust air flow is definitely altered, you can feel that just with your hand. That makes me think that using some type of channeling steel will help. By the way, the buffer plate is not sagging from the paver weight, it was actually deformed like that when I bought it (used). I assume it was from the intense heat.

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Halleys5
 
Hot Air Coal Stoker Furnace: Reading Juanita
Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing II