subdividing a one-zone forced-air system?

Old 10-08-08, 01:57 PM
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subdividing a one-zone forced-air system?

Subdividing a one-zone forced-air gas central heating system?

I have a small 50K BTU forced-air gas furnace in my new 1450sqft home; it is controlled by a single programmable thermostat in a large first-floor room, but provides heat for the entire house through 1st floor hot air supply ducts in the floor and basement supply ducts in the ceiling.

I'm pondering the advisability of splitting this system into two or even three zones (east, west, upstairs). I was wondering if anyone has had similar experience zoning out a one-zone ducted heat system.
Old 10-08-08, 02:54 PM
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Please, don't even think about zoning that system. Zoning of residential forced air systems is usually a mistake and the smaller the house the bigger the mistake.

Your furnace is designed to have a specific airflow through it when operating. Trying to zone your system will cause a much smaller airflow through the furnace and at the very least will significantly lessen the life of the furnace and at worst could cause the furnace to overheat and start a fire in the house structure.

Sometimes larger systems can be successfully zoned but they require specially designed ductwork and special furnaces. Even in houses of 5,000 square feet it is usually better to install separate systems than to zone one large system.
Old 10-09-08, 07:20 PM
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The system you are talking about zoning is a bit small although Many systems are successfully zoned by people who know what they are doing the price tag has 3 zeros on it and especially if you want 3 individual controls you could get a new system for what that will cost.
You can't just shut off air flow because your furnace needs a certain amount of air to operate safely not to mention efficiently so when you close off air the same volume of air needs to be added back to the return via a bypass damper all these dampers need to be connected to a central control and adjusted carefully.

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