What makes a fireplace draw

The two main things that contribute to draft size are:. The reason that a taller chimney creates a better draft is really rather simple as the higher up in the atmosphere the chimney reaches, the greater the differential pressure. Expert masons will tell you it's much easier to decrease a draft that is too strong than it is to improve the draft on an inadequate flue. With that being said, if a larger draft is better why wouldn't chimneys just be built 20 feet into the air?

The reason is that a draft can only flow through the capacity that the flue can handle and any more is overkill.

Truthfully when a draft is too big for the flue to exhaust, smoke and gas can potentially bellow back into the home which is extremely unsafe. The general rule of thumb is that the floor where the fire source fireplace, wood stove is located to the top of the chimney should never be less than 15 feet and the distance from roof surface to chimney top should be aimed for 3 feet.

When a house is repeatedly filling with smoke or the fire is slow-starting it's easy to think that the chimney height is not adequate. One fix that people might immediately jump into is to purchase chimney extensions that will raise the overall height. While this definitely might resolve the issue it's still best to confirm that the draft problems aren't caused by a blocked flue, unseasoned wood, or a depressurized home. Ultimately, it's best to have the issue looked at by a trained masonry expert before attempting "trial and error" fixes.

Debris can gather further up the chimney, and birds can even nest. Having your chimney swept as regularly as possible is one of the main ways you can help to improve how well your chimney is drawing on your fireplace.

For a chimney to draw well on a fireplace, the hot air that is lost up the chimney must be replaced by other air from within your home. The issue of a vacuum being created can be more of a problem in newer homes, where they are built to higher standards and less air will naturally make its way into a house. Opening any external air vents located in the same room as your open fireplace will help to supply a fire with as much fresh air as possible.

By providing a fire in an open fireplace with a source of continuous fresh air from outside your home, it can help to maximize the draft on your fireplace. Opening any vents or windows can also help to prevent a fireplace from pulling warmer air out of other parts of your home.

In order to help improve the draft as much as possible, If your fireplace has a damper it should be fully opened prior to starting any fire. A fireplace damper is typically located within the lower area of a chimney, just above the fireplace. Dampers are typically controlled by a handle, which in many cases can be used to set the damper at a partially open position. Other types of damper can be found at the top of the chimney, in which case there would be chain hanging down into the fireplace opening.

Setting a damper partially open can help to reduce the draw on a fireplace, and so to improve the draft the damper must be opened as wide as possible. For more information about dampers we have another article explaining them in much more detail here. If your fireplace has glass doors, try to leave them open for a short period of time before each fire to help bring both the fireplace and the chimney closer to room temperature. A fireplace with closed glass doors means that the fireplace can be cut off from the warmer room temperatures of your home.

It can be harder to start a fire in a cold fireplace because there may be insufficient draft for the fire to get going well. While hot air rises, cold air sinks, and cold air within the chimney can push down on the fireplace, and prevent the chimney from drawing on the fireplace properly.

This can help bring up the temperature within the fireplace and make it easier for the draft to be started. Warming up the air within a chimney, also known as priming the chimney, can help start the draft even before a fire has been started.

As we use newspaper as our fire starter, we simply take another sheet of newspaper, roll it up and light it at end, place it within the top area of our fireplace and leave it to burn through. By warming up the air within the chimney before starting a fire, it can give the fire a better chance of success.

An easy way to test if pressure differential is causing the smoke draw issues is by holding a burning stick of incense in the throat of the fireplace. If the smoke goes up the chimney, pressure differential is not your culprit and you can move on. However, if the smoke from your incense blows down and back into the room, that means your chimney has a downdraft. You can do this by opening a window or door low in the house, turning off a fan or your furnace or closing upstairs windows.

Try these things one at a time while still using your incense to test and give the air enough time minutes to reverse itself. See what it takes to control the indoor air pressure so that there is no downdraft in the chimney and the smoke begins to draw upward. Please note, every home is different so what works for one may not work for all. A good rule of thumb is to think about reducing the air escaping high in the house and increasing the air coming into the house on the lower floors.

Note, it may make a difference which window you open or close, especially in a breeze — when you open a window, check to ensure the outside air is actually flowing in. Modern houses tend to be very tight think spray foam insulation, house wrap, weather-sealed windows, etc. Because these homes are so tight, it is difficult for ventilation and combustion air to easily enter the home, meaning that there is not enough makeup air in the house for the fireplace to draw properly.

Then add ventilation air opening a downstairs window that is blowing air into house, etc. Going through this process will help you determine how much air is needed for the fireplace.

While the quantity of combustion air required varies based on the type of fireplace, type of chimney and size of the fire that is burning, a general rule of thumb is 1 cubic foot per minute of make-up air per 1 square inch of flue area.

For a permanent fix, you can install one of the following:. Two of the most common weather culprits are extreme cold and cross drafting. In very cold temperatures, an unused flue can fill up with high-density cold air that itself blocks the flow of smoke up the chimney. This is especially true if your chimney is located on the outside of the house. In these cases, take steps to "warm" your flue by building a small fire of newspaper at the back of the firebox.

Continue to feed more newspaper until the smoke from the fire disappears up the flue. Wind can cause smoke issues a couple of different ways. The first way is known as Dynamic Wind Loading.

This is caused when wind blows on one side of the house, causing a high-pressure zone on that side of the house and creating a corresponding low-pressure zone on the other side of the house. This causes a pressure differential, which can be solved by opening a window on the windward side of the house. Wind can also cause turbulence at the top of a chimney, not allowing the smoke to escape, or can even blow the smoke back down the chimney into the fireplace.

This is especially common if there are tall roofs or trees nearby. You can fix this by replacing your rain cap with a draft inducing cap. The stack effect describes the movement of air into and out of the building, chimneys, stack, etc.

In most homes, there is typically a neutral pressure level about halfway between the ground floor and the roof, meaning everything above that level is positively pressurized air will leak out and everything below is negatively pressurized air will leak in. In older houses and oftentimes tall houses, the negative pressure rarely exceeds 8 Pascals, which is about the difference in pressure in 10ft.

Furnaces and fireplaces usually perform well pulling against a negative pressure of up to 8 Pascals. Modern houses, however, tend to be more tightly built using spray foam insulation, caulked windows and sealed doorways. They also tend to be full of powerful kitchen and bathroom exhaust fans, so the neutral pressure level may be higher in the house if it exists at all.

This means the negative pressure in the lower areas of the house can far exceed 8 Pascals, causing a downdraft in a chimney. You can help reduce stack effect in your home by stopping air leaks in the uppermost parts of your house, including attic access hatches, ceiling light fixtures, and poorly fitting windows.

In this case, the stack effect can only be corrected by adding as much air to the house as is being blown out of it, i. Chimney height can also create a downdraft situation if the chimney does not extend high enough into air with a low-enough density to create an ambient updraft.

In general, a taller chimney will typically draw better. If your fireplace smokes because your chimney is too short, the problem is likely worse when the wind blows.