How do you calculate air flow in a chimney?

Required chimney area can be calculated as A = Q / v (3) where A = cross-sectional area of chimney (m2) Q = volume of flue gases at chimney temperature (m3/s) v = velocity (m/s) In general 1 kW boiler heat requires 1100 mm2 of chimney area.

How do you measure a chimney draft?





Normally we measure draft at two locations: over the fire or in the combustion chamber where typically we may see -0.02 to -0.03 inches of water column pressure, and in the breech or at the stack pipe (properly, the flue vent connector) measured just a few inches above the boiler or furnace top, and before the

How do you measure the air flow?

By multiplying air velocity by the cross section area of a duct, you can determine the air volume flowing past a point in the duct per unit of time. Volume flow is usually measured in cubic feet per minute (CFM).

What airflow velocity do drafts begin?

Indoor air velocity

0 m/s Stationary air. Note, minimum air change rates are required to maintain indoor air quality.
0.3 m/s and above May be felt as a draught in a cold climate in the summer.
0.8 to 1 m/s and above May be felt as a draught in a hot climate.

How are drafts measured?

Draft intensity is measured in “inches of water”. Just as a mercury barometer is used to measure atmospheric pressure in inches of mercury, a draft gauge is used to measure draft intensity (pressure) in inches of water. Natural Draft is thermal draft. It occurs when heated gases expand.

How much air goes up a chimney?





A conventional fireplace exhausts as much as 24,000 cubic feet of air per hour. So, it’s essentially like shooting 400 basketballs out your chimney every minute.

How much draft should a chimney have?

Generally, the more distance you have between the hot fire and the outside cold air will create a stronger draft. Wood stove manufacturers generally state that the minimum chimney height should be no less than 15′. Based on their tests, 15′ is the height where you will start to have an optimal draft.

Does a longer chimney increase draft?

Height: the taller the chimney, the more draft it will produce at a given temperature difference.

Does a chimney cap Reduce draft?

However, did you know that chimney caps can also improve the draft in chimneys? Draft issues can contribute to smoky air and unpleasant odors entering your home as well as toxic gases like carbon monoxide lingering inside your chimney for longer than they safely should.

What is a good air flow rate?



Air Flow Rates (CFM) in Buildings
Carson Dunlop Associates’ sketch points out that the (typical) desirable rate of cool air flow in an air conditioning system is around 400 to 450 cubic feet per minute.

What is the acceptable air velocity?

The study also identified an acceptable air velocity range from 0.3 up to 0.9 m/s under the experimental conditions. This velocity range is relevant for the design of personalized ventilation in practice.

What is the difference between air flow and air velocity?

Flow is a measure of air output in terms of volume per unit of time. The common units are litres per minute, cubic feet per minute (CFM), etc. Velocity refers to how fast the air is moving in distance per unit of time. The common units are feet per second, metres per second, etc.

What is chimney draft?



This movement of combustion air and exhaust is called draft. In essence, it is the difference in pressure between the air/gasses inside the chimney flue and the outside air that creates this movement. Warmer, lighter gasses in the flue tend to move upward.

What is draft pressure gauge?

An instrument used to measure the small pressure differentials below atmospheric; e.g., an inclined manometer to measure the pressure difference between a flue and the atmosphere for combustion control.

What is a draft test?

Draft testing is an essential skill you need to diagnose carbon monoxide (CO) problems. Draft is the force that controls combustion air to the burner. Your job is to assure draft pressure is kept within specific boundaries. Be careful, however.

How do I find drafts in my house?

If you feel a soft breeze when you stand close to a window or door, a draft is near. Turn off any appliance that creates an air disturbance, like the stove. Walk around with a lit candle or a stick of incense. If the flame flickers or burns out, a draft is near.

What is a chimney draft inducer?



Draft inducers are electrically operated devices which increase the air flow up a chimney. This action increases the negative pressure (draft) in the stove, preventing smoke from leaking out of pipe, seams or doors.

How do you check Backdraft?

To check for proper draft, I simply cup my hands around the draft hood without actually touching it. If the water heater is backdrafting, I’ll feel warm, moist air coming out of the draft hood.

How do I prevent backdraft in my chimney?

How to Prevent Chimney Downdraft

  1. Shut Off Exhaust Fans: When your fireplace is in use, turn off your exhaust fans, as they naturally increase negative pressure by pulling air out of the house.
  2. Adjust Your Damper: If your damper is warped, you might need to adjust it slightly to get the right airflow.

What is a common indicator of backdraft conditions?

Conditions for backdraft might include: Black smoke becoming dense, greyish yellow without visible flames. The smoke color is indicating incomplete combustion. Usually the darker the smoke the more incomplete the combustion.