If your house is small and not insulated, there are going to be days when any system cannot keep up with heat loss (unless your curnace is massively oversized). Big houses fare better because a lower percent is exterior wall, and a well insulated house should retain heat for much longer by slowing heat transfer.
I'd sooner invest 3x the money in insulation (if it cost thaf much) rather than overtaxing the heating system.
