We have a Lennox high efficiency model g32 Dimension gas two stage forced air furnace. It has been in place for about 1 year. Prior to that we heated with oil fired forced air(for about 15 years). We have always closed the hot air registers to rooms not used during the day, such as bedrooms,2fl bath, etc. Now that we have an empty nest we also close registers off to several rooms that are not used. Along comes Dave Lennox's friend who tells us this is not good. We should leave registers open as furnace is not working to it's capacity.
Our position is: When the furnce has less area to heat, more heat will go to those areas that require it; thus cutting down on amount of energy required for the heated area. Our thermostat is located in an area that is heated 24/7. Common sense says the smaller area to heat, the less cost.