I recently removed a gas fueled furnace and its ductwork and replaced it with a multi-zone heat pump system in my 1940s home. The house is just over 1000sf but will soon have another 900sf of living space when I complete the finishing of my basement where I removed the ductwork and furnace. 

I’ve been pretty satisfied with the performance of my ductless heat pump system during the warmer months but last winter my system sometimes struggled to keep my indoor air temperature at a comfortable set point. In the coldest months I would often find the indoor air temperature getting down to the low 60s – possibly colder in some of the bedrooms. I can handle that low of a temperature but I’m not comfortable having very young children having to sleep in a cold house. 

Some day I would like to do an energy retrofit to add more insulation in the attic and the exterior wall cavities but for now I am entertaining a redundant heat system with gas fueled fireplaces. I am considering an insert for my fireplace upstairs and a gas fireplace downstairs. The challenge I’m having is that I’ve been told that despite my chimney having two flues, the vents for these fireplaces would potentially be too close to each other since the chimney flues are somewhere between 2′ and 3′ on center. 

It would be possible to add a metal divider between the two vents or to make one vent several feet higher than the other (not necessarily the aesthetic option I’m looking for) but I don’t know if the divider would do enough to separate the exhaust from one system mixing with the intake of the other. I am expecting the vents to be a Duravent’s DirectVent high wind product.

Should I be concerned about the vents being so close to one another? If it is going to be an issue – and I cannot find a different venting solution – I’ll live with just the gas insert on the main level but it would be nice to have one in the basement for the warmth and ambiance. Thanks in advance for your suggestions.