Apparently the article may not be entirely accurate.
Read this section I posted below in blue.
"For furnaces, you have a choice of single stage, dual stage and dual stage variable speed units. In a single stage unit, all the burners ignite every time the furnace turns on regardless of outside temperatures. In a dual stage unit, only 60 percent of the burners turn on initially. If the thermostat is not satisfied within a short period, the rest of the burners turn on. Dual units save homeowners gas and energy costs. "
Dual units save money....meaning they are more efficient?
What do you think?
In the land of the blind.....the man with one eye is king....