Downsizing furnace for zoned system

[markaschheim]

I'm going to have my single story house zoned; bedrooms heated at night and kitchen/living room heated during the day. It's heat only since summers are not hot here. One contractor suggested I could save some $ by reducing the BTU of my furnace--plug one of the manifold ports to eliminate a burner, put in a smaller gas valve, and change pulley diameters to slow the fan. Is this safe or not? Certainly is less costly than a new smaller furnace.

Thanks.

[beenthere]

Could actually cause you to use more gas.

[BobbyBJr]

You need a load calc done to know exactly what size furnace you need to do what you want it to do. Personally, I wouldn't plug any orifices.

[Air Tight]

That is commonly known as a "Hack" in our industry. In the long run your probly going to spend a dollar later in repairs to save a dime today. The unit should be sized to maintain your heat loss for the whole home. If your going to zone spend the money to do it right, buy a 2 stage. Besides if he uses a bypass on the zone system theres no reason for all that mickey mouse stuff.
Removing burners/orfices is call de-rating and should involve the manufacture to ensure it's done properly. But then your furnace maybe to small to keep the home warm in the dead of winter.

[docholiday]

use a manual J 8 load calc. For the most part your system is installed for the worst case and when it's that cold out, more often than not, all zones will be calling requiring the full size. That said, in cooling you may be able to reduce because one zone may not have a full load at the same time another does because of the sun and orientation of the home. Manual J 8 will take this into account and will provide you peak load information.