Stopping Back Draft and Improving Steam Evacuation

Back draft can occur in both your Steam Stack AND your Smoke Stack. There are many potential causes. It is important to address and fix the back draft so that you can have a healthy, clean fire and so that smoke/steam do not overwhelm your sugar house.

Cause

Solution

Make-up Air By FAR the biggest cause of poor steam evacuation is lack of make-up air. In other words, your building may be having trouble recovering the air that is being sent out of the stack pipe(s). Remember, your evaporator is pulling A LOT OF AIR OUT OF YOUR BUILDING. If your evaporator has forced draft, they can add up to over 1000 cubic feet per minute — thats just in combustion air. The rear hood — when under full fire — is drawing another 1000 CFM. Cracking a door or a window may just not be enough to keep up with this.  When there is a lack of make-up air provided, the evaporator will pull it down through your steam pipe, pulling all of that condensation down into your room.

Sometimes opening a window or door on a given side of your building can make this WORSE.  The make-up air, on a windy day needs to be invited on the wind side of the building, NOT the side where the wind is blocked.

If all else fails, a make-up air fan can be employed.  A make-up air fan must be sized appropriately. The fan blower can be a low pressure unit, but it’s volume must be able to overcome ALL of the appliances drawing from your building, evaporator combustion/evaporator steam/water heater/non-high efficiency furnace/boiler/bathroom fans, etc. With this, you’ll leave your doors and windows closed, the fan will balance the pressure in the building.

Window As mentioned above, it can help to open a nearby window. However, wind direction will influence which window you should open. Make sure the air from outside is coming into the building to pressurize the room. In contrast, if the air from inside is flowing outside, close that window and open a different window on the opposite side of the building.
Fans If there is a fan running in a nearby bathroom (for example), this suction may be affecting the pressure in the room. Turn off any fans that could be creating negative pressure.
Cold Air If there is cold air in your chimney, it may be be falling downward and disrupting warm air that is trying to rise. Once the chimney warms up, the draft will correct itself and move upward.
Blockage If there is a cover on your smoke stack, make sure it is opened/removed. There could also be creosote/ash build up causing blockage.
Stack Height The general rule of thumb is that your stack pipe should be double the length of your pans, up to at least 12 feet of stack pipe.
Wood Stick to using well-seasoned, non-resinous firewood. Wet wood produces much more smoke and can not burn as hot/efficiently. If you see moisture bubbling out of the end grain of your firewood in the fire, that is sign that it is extremely wet.
Arch Blower Always make sure to turn your blower off before opening your firebox door.
Down Draft Wind that is blowing across the peak of your roof can create a down draft into your stack/steam pipe. Down draft can disrupt the steam/exhaust as it is trying to rise and evacuate.

Arches by Smoky Lake Maple Products