No boil in flue pan

[Sunnyacres]

This is our first year with a flue pan and it doesn’t seem like it’s boiling hard it only boils the in the front 8inches of the flue pan . Is that normal? I have a 2x4 drop flue pan and a 2x3 syrup pan and the syrup pan boils fine. There is a 1/2” under flues and running AUF with 14’ feet of stack. I’m not sure what could be wrong. I do have a cap on the stack as I saw in another post that could be the problem but I thought the flue pan would boil like crazy.

[RileySugarbush]

Get a probe type stack thermometer if you don't have one. That will help diagnose the problem. The sap pan is easy to get boiling since it receives radiant heat from the fire as well as the conduction heat transfer from the combustion gases. It is possible you have too much AUF for the amount of wood you have in there, resulting in air passing your fire and cooling the exhaust gasses. The thermometer in the stack will help figuring that out.

Maybe try keeping more wood in the firebox at time and/or cutting down the AUF a bit and see what happens.

And brush the soot off your flues each time you boil. That can reduce the heat transfer too.

[Sunnyacres]

The fan is on a VFD and I have tried it on all settings. We get lots of steam but not a hard boil. It does start boiling a little harder when we shut the fan off and open the ash door. But not nearly as much steam.

[n8hutch]

When you say that you have a half inch under the flue pan is that the full length or just at the end?

[western mainer]

How much sap do you have over the flues? 3/4-1"? and did you close up the end of your evp. by the stack alittle bit to hold in the heat?
Brian

[Sunnyacres]

The whole length of the flue pan

[Sunnyacres]

How much sap do you have over the flues? 3/4-1"? and did you close up the end of your evp. by the stack alittle bit to hold in the heat?
Brian

I didn’t close up the stack. And I run 1 3/4” in both pans

[Sunnyacres]

So I came home and took the stack cover off and it seems to boil faster but still not a hard boil in the flue pan.

[ecolbeck]

We get lots of steam but not a hard boil. It does start boiling a little harder when we shut the fan off and open the ash door. But not nearly as much steam.

This is confusing. How can you have more boil and less steam?

[Sunnyacres]

That’s what I am wondering if I shut the fan off the front half of the flue pan has large geysers but the steam seems to drop compared to when the fan is on.

[Woody77]

Is the boil in the flue right at the transition of the ramp in the arch. And no further back from there. As for the steam it could be a couple things. The hotter the steam the less visible it is cause its vapor not steam. If that makes sense. That being said if you are evaporating faster you bring in sap faster witch keeps the visibal boil down. The only way to be sure witch way is better is to keep track of your gallons per hour of evaporation.

[DrTimPerkins]

Doesn't sound like your issue, but sometimes the flue pan partition where the sap or concentrate comes in will boil less vigorously due to the fact that cold liquid is coming in there and has to be heated from around 40 deg F to 212 deg F as opposed to the other side where it might go from 212 to 215 deg F or so.

[Sunnyacres]

Going to add another section of pipe today and see if that helps. It certainly seems to boil better without the fan on and the door open. Maybe the fan is too small it’s just a small squirrel cage blower with a 2.25” round opening can’t remember cfm I will have to check when I get home.

[Super Sapper]

The fan is on a VFD and I have tried it on all settings. We get lots of steam but not a hard boil. It does start boiling a little harder when we shut the fan off and open the ash door. But not nearly as much steam.

This would indicate that you are getting more air with the ash door open than with the blower. Your blower is too small.

[Sugarmaker]

Geysers good. Some pans never get that same action in the back. Your loosing heat as the flames and heat move through the pan length. Mine doesnt boil hard in the back either.
Regards,
Chris

[mellondome]

Your fan is too small. If you are going with forced air, your stack height will make no difference. It will only effect natural draft. Those little fans are not enough for a 2x6. When my 2x6 was wood fired, i used a 465cfm blower with a reostat on it. Would go full air immediately after adding to the firebox then back down to about 3/4 speed for the next 5 minutes before adding wood again.

[maple flats]

Also, what size do you have your wood split at? Is it essentially wrist size and it the wood dry?
Any squirrel cage blower I've seen with just a 2.25 inch round exit is way too small to feed that arch. You need more air.
Rather than that blower you will likely do better just using the vent door, under the grates, open it up at least 6" and see how that helps. That along with the wood dry and split to wrist size will do it, because your stack it tall enough for that arch.
The space under the flues should be about 1/4" to force the heat up thru the flues.

[Sunnyacres]

Most all my wood is wrist size slab wood mixed with some larger hardwood.. keeping the door open and filling every 7 minutes has helped and the syrup is starting to lighten up a bit in color but I think I will order a bigger fan. How many cfm should I be looking for.

[maple flats]

Keeping the air vent door open is good, the fueling door open is bad. Which is it? When you add fuel you should have it set up right where it can be put in quickly and get the door closed ASAP. The temperature in the pans drops as soon as you open the door. If you have a double door, open just 1 to fuel, fill that side, the next time open the other and fuel that side. If you have a single door, just be quicker, but be careful not to hit the syrup pan bottom or the flues pan at all. My previous set of pans were second hand and the front of the raised flue pan had dents in it, not real bad but dents none the less. Be careful and quick adding wood.

[Sunnyacres]

We keep the ash door open. Any ideas on fan size?