Every HVAC contactor who I have received a quote from says that for a high efficiency furnace w/central air that I realistically need return vents in every room. I understand the reason why I need return vents, but I'm not willing to shell out the extra $ to put returns all over the house since I live in a region where central air is not a requirement for comfortable living in the summer time (I have large trees on the South elevation which provide substantial shade to the house in the summer). I currently have an ancient Lenox Aire Flo K5-135M (135k BTU input / 108k BTU output) with the air intake on top of the furnace and a single return opening through the first floor living room.
The question is whether it is possible to have a high efficiency furnace without return vents? (the furnace is in the basement). I'm willing to have a lower efficiency unit without central air as a trade-off for not having to spend the extra $ to put returns all over the house. If I go with a lower efficiency unit, what percentage efficiency might it be, and what would be the best make/model for this type of scenario/design?
Thanks in advance for any advice,