A downdraft is when the air is blown back down the chimney. Stopping smoke and gases from rising and getting out. You’ll actually be able to see the smoke struggling to exit. There are several reasons why this can happen. And you can take steps to prevent it. See how to stop downdraft in chimneys here…
To understand why a downdraft happens you need to know a little about the operation of the chimney. It all depends on hot air rising – the hotter the fire the faster the air rises. The current created draws air from the fireplace surround, feeding the flames as it passes the fire.
Hot air rising results in different air pressures throughout the house. Low pressure in cooler areas. And high pressure where the warm air collects. If the low pressure is beneath atmospheric pressure your chimney may have a downdraft ongoing.
With energy efficient new build houses becoming more popular changes in air pressure can also change the fireplace airflow. Fan assistance is required for tumble driers, extractor fans, dehumidifiers, microwaves, and computers. And these all make the pressure in the home unstable. This negative pressure can be equalised with the installation of a makeup air kit.
Other Downdraft Causes
If your fire smokes when you first light it this could be due to a cold flue. You can pre-heat the flue by rolling a piece of newspaper, lighting it, and reaching up the chimney as far as you can. This should draw the smoke into the flue rather than into your home.
Burning wood with a high moisture contact may be the culprit. Different wood species have different moisture contents. Burning fuel that is mostly water will result in low fire and flue temperatures. Choose firewood with a moisture content below 20% for efficient burning.
Tall trees and buildings nearby can affect wind currents. And can cause downdrafts. A simple smoke test can help to determine airflows around the chimney – you should consult a fireplace technician. You may be advised to add a flue stretcher or an exhaust fan. And a wind-resistant chimney cap would be another option.
A poorly constructed or broken chimney will cause downdraft issues. As will an obstruction. Blockages may be formed due to a build-up of creosote and this can result in a smoking chimney. And chimney smoke in the room. You’ll need to get your chimney professionally cleaned if this is the case.
It’s important to recognise that chimney cleaning can keep your home and your family safe. A clean chimney also means a more efficient fireplace. And allows smoke, toxins, and dangerous fumes to escape. Periodic chimney cleaning will reduce the risk of a house fire. And prevent costly chimney repairs.
If your chimney is too low you may have to increase the height of the stack. Although this can be costly. Twin wall flues can be increased in height by adding an extra length.
Alternative Downdraft Solutions.
Anti-downdraft chimney cowls can be fitted to the top of the chimney or flue system. The cowl is designed to fit onto the chimney pot. As well as minimising rain access, it prevents animal and bird entry. And the aerodynamic shape of this cowl makes it ideal for dealing with negative pressure.
Make sure the chimney can operate to its optimum. And that the flue has been installed to the manufacturer’s guidelines. Generally, a flat-roofed house should have a flue extended about two metres above. And a 600mm flue termination for a pitched roof.
The flue needs to be well insulated. With sealed joints. And your home should have insulated walls and ceilings. Remember that there’s a relationship between the fan operation of household items affecting negative pressure. You may just need to open a window for added ventilation when these fans are being used.
Adequate air change is essential to ensure that your chimney functions well. And doesn’t pose any risks to health. Poor internal air quality can cause an unhealthy living space. And hazardous pollutants can gradually build.
Replacement Fireplace Installation
If you decide to update your existing fireplace, or want a completely new one, choose a trusted company to carry out your service. Get a complete package. A free estimate. And arrange chimney sweeping and cowl fitting all at the same time!