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Short Explanation on How Does a Furnace Work

Say you’re thinking of getting a new furnace or you’ve just got one and you’re not exactly sure how it works. Knowing how appliances such as furnaces work is crucial if you’re to be able to do proper maintenance and troubleshooting. Not to mention that it will help you understand how to use them as effectively and efficiently as possible.

So, here’s our short explanation of how furnaces work.

How does a furnace work?

There are 3 main types of furnaces you can have and they work in different ways – the gas furnace, the 2 stage furnace, and the wood-burning furnace.

How does a gas furnace work?

A typical forced-air gas furnace works in the following manner:

  1. The propane or natural gas gets ignited in the furnace’s burner.
  2. The flames from the gas heat up a metal heat exchanger and they leave the furnace through its exhaust and flue.
  3. The now hot heat exchanger warms up the air that’s going around it.
  4. The blower forces of the furnace distribute cold air to the heat exchanger and the warmed-up air through the ductwork and back into your home.

How does a 2 stage furnace work?

So, not that we know how a normal gas furnace works, how does a two-stage furnace work? Most of the process is exactly the same as the one above. The difference is that while “normal” gas furnaces are “one stage” furnaces, two-stage furnaces have an extra position of the gas valve.

In essence, a standard “one-stage” gas furnace has two positions for its gas valve – “open” and “closed”. When the valve is open, gas is flowing through and is heating up the heat exchanger and when the valve is closed, the furnace is not working. The unique thing about two-stage furnaces Is that their valves have a third position which is “partly open”. This allows the furnace to let a bit less gas through (usually about 60% – 65%).

This makes two-stage furnaces more efficient as they can use less gas when the thermostat tells them they don’t need to work at 100%. Aside from that, these furnaces work in the same way as standard “one-stage” gas furnaces.

How does a wood furnace work?

The difference between a wood furnace and a gas furnace is solely in the way the forced air gets heated. The heat exchanger of wood forced-air furnaces is the firebox itself – the furnace where the wood is burning. The forced air is then blown around the hot firebox until it’s heated up and it’s then distributed through the pipes the same way as in gas furnaces.

The chimney of a wood furnace comes out of the firebox as it would out of a fireplace and exhausts the smoke outside. In fact, the forced air also often circulates around the outer wall of the chimney so it too can act as an additional heat exchanger. All that is wrapped in insulation and the whole system is typically located in a separate building outside your house with the air pipes running underground back to your home.

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