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how do furnaces work?
- little_ranni (age 15)
Great question! Furnaces work by burning fuel (like oil or natural
gas). When these things burn, they form hot gases that are sent through
curving metal tubes called 'heat exchangers.' The heat exchangers are
inside of the air ducts in your house, so the air in the ducts gets
warmed up by the hot metal pipes. Then they use fans to move the warm
air out of the ducts and new air in. Since the potentially toxic gases
from burning the fuel stay inside the heat exchanger tubes and the air
in your house stays outside of the tubes, the air in your house can't
You may also want to take a look at the answer to the question 'How do thermostats
(published on 10/22/2007)
Follow-Up #1: efficient air conditioners and heaters
What type of furnace and air conditioner, are the most efficient? Or better yet...If you had to install a new furnace and central air unit, what would you have installed?
- Chad Lynch (age 40)
North Platte, NE -- USA
I'm thinking of getting some electrical heat pumps. These are air conditioners in the summer but can run in reverse in the winter. The beauty of using a heat pump is that for each Joule of electrical energy used you can pump something like 5 J of heat into the house. That high efficiency more than makes up for the inefficiency of generating electricity from burning fossil fuels. In addition, as non-fossil electrical power becomes more common, you'll have a very environmentally sound and efficient heating/cooling system. The primary drawback is that in extremely cold weather (which you sometimes get in NE) they lose a lot of efficiency and have trouble providing enough heat. If you have some land, that can be avoided by having the heat exchange with the ground via pipes rather than with ambient air. Of course that raises initial capital costs. Otherwise you need to supplement them with a conventional furnace for the worst of the winter, as one of my neighbors (a nuclear engineer) does.
These units typically come with separate air handlers for each room, each with its own thermostat. There's no duct work. Each heat pump usually powers several such air handlers. One of the main efficiencies is that the separate air handlers make it easy to mostly just heat and cool the rooms that are in use.
(published on 11/16/11)
Follow-up on this answer.