Forced Air Again

[Sugarbear]

We have a wood fired 3X12 King with an eight ft flue pan.We just cant seem to get it boil like it should.We installed extra insulation on the sides of the firebox and the doors and jacked it up to get more air in it.These things helped but it still wont go like it should.With our sugarhouse located in the woods we are thinking that we just are'nt getting enough natural draft.Forced air is the next step.Can anyone tell me the approximate cfm blower I would need.I am planning on concreting the sugarhouse floor soon and was thinking of having the blower in the corner and running a duct under the floor to arch.Anyone have any thoughts on how that would work?Thanks,Terry

[Sugarmaker]

SugarBear,
We are using a 550 CFM Dayton squirrel cage type blower which has two speeds. Probably a 600 or 650 might work for you? Ours is mounted under the rig but you could mount it out side and pipe in to the fire box. Our sugarhouse is in the open and on a hill so we have very good natural draft also ( 20 foot of 12 inch dia stack). What is your stack height? Should be about 24 feet.

Regards,
Chris

[gmcooper]

I na conversation with Bruce bascom a couple years ago he mentioned with the longer evaporater it takes really good wood to get the full benifit of the longer flue pan. We were talking about the difference in a 3x8 vs 3x10 or 12'.
Forced draft might help make up some of the difference. Our first forced draft cfm info from Leader was way under what we had to use. We ended up going back to natural draft that year till we put in a much bigger unit.
Mark

[802maple]

I would run the blower outdoors as that is where your best oxygen is. Some of my customers have run there duct work inside or under their cement floor with great success. A 600 cfm or above blower will be what you need, I personally would run somewhere around 750, you can always slow it down if needed.

Jerry

[Father & Son]

The blower size is based on stack size.

The formula to figure stack area is pi x radius squared, pi = 3.1416, so the area of my 7" stack worked out like this

3.1416 x 3.5 x 3.5 = 38.48 square inches

38.48 square inches x 3 cfm/square inch = 115.44 cfm's

Correct me if my math is wrong but this gives you a way to figure what size blower you need.
I bought a 265 cfm blower just to give me some flexability for later improvements.

Jim

[danno]

As has been said before - placing the fan outside also reduces noise inside. I love forced air, but the droning fan noise becomes a nuisance imo. Definetly running my fan from the outside this year.

[802maple]

Father and son your mathematics are right for a volume of air that a stack will handle but you want to create positive pressure in your arch, that being approximately 5 inches. So it needs to be a little more than what your stack wll handle.

[WESTVIRGINIAMAPLER]

Leader sells a 2.5 x 8 with a 900+ cfm blower, so I would definitely put one around 1,000 or 1,200 if you are using a regular squirrel cage blower. If it is high pressure blower, it might not need to be quite as high. Better to have too much and turn it down vs not having enough.

[Sugarbear]

Thanks for the input everyone.I was thinking putting the blower outside as it could be easily done.It was a space issue for me but I had'nt thought about the noise and better air.Again,thanks

Terry

[WESTVIRGINIAMAPLER]

Terry,

If you are going to put one outside, a high pressure would be better as the air is going to be traveling a longer distance and you will likely get better combustion also with the high pressure.

[brookledge]

sugarbear
How many gallons per hour are you getting now?
Keith

[Father & Son]

802maple,
I can see what you mean with the positive pressure if you have an airtight arch, mine isn't. I could only run it at a very slow speed or it would blow ashes between the doors. High speed made it look like it was snowing inside the sugar house. That formula came from another trader a couple of years ago.

Jim

[802maple]

Yeah my experience was the same with my first blower. It made a whale of a mess. I know exactly what you mean.

[Sugarbear]

I know what that "snowing" is like.Last year at the end of the season we had a really big run.I didnt have the best wood and it was taking forever to get it all boiled.Out of desparation I put an old furnace blower that we use for a fan for the cows when it is hot and stuck it in front of the evaporator.It blew way too much air and I had to keep it back about six feet from the evap. It helped alot but I had ash blowing everywhere.

Keith,At best we 80-90 gal/hr and sometimes it is more like 60.It would vary alot with wind speed and direction.

[brookledge]

sugar bear
Have you tried to add length to your stack? The recommended length is 2 times the length of your arch but that doesn't mean you can't have more.
With my wood fired 3X12 I'm getting 140 GPH. That is with a inferno arch with forced draft and a pre-heater.
So at 80-90 with a basic arch and pans that is not too bad.
Keith

[Sugarbear]

The stack length is 25 feet.