Heat pump or efficient furnace for old Midwest house
Hello GBA, I would appreciate input or direction to existing articles that would help us make a decision on a suitable gas furnace replacement. We have an 1890 masonry ‘ worker house’ in the upper Midwest and are planning multiple upgrades, including attic insulation, new windows and doors. Our first floor and basement uses a gas powered water boiler for heating. We installed a split system several years ago to provide cooling in the summer. The upstairs, approximately 800 SF but with lots of windows and skylights, has an existing gas furnace with short duct runs. It provides heat and cooling but is very loud and inefficient. For our forthcoming work we want to include an upgrade to this 2nd floor system. We would prefer to not upgrade all the mechanicals because we are already pushing our budget limit. I am concerned that replacing the furnace with ducted heat pumps will not provide enough heat. Our exterior walls remain uninsulated, and we have many windows and skylights. We would also still need gas service due to the boiler. Thoughts and recommendations would be greatly appreciated.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I know you are planning on upgrades, but best place to start is to see what your existing heat load is. This is a quick way to get that based on heating bills:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
As for fuel burner VS heat pump, lot of it comes down to local utility rates and if you need AC. If you need AC, the cost delta to heat pump is pretty small equipment wise and pretty much the same install labor. Generally the simpler option as you don't have to deal with gas or venting combustion. There is even stuff like this out there that you can DIY as the refrigerant are quick connect, pretty simple swap to an existing furnace:
https://mrcool.com/mrcool-universal-series-dc-inverter-heat-pump-air-conditioner-split-system/
If you are connected to the city gas system generally gas will be the lowest cost to operate option.
Before you insulate you need to keep the wind from blowing the warm air out of the house by air sealing with blower door before and after testing. Then you can think about insulating.
Consider lowering your heat loss by eliminating the skylights and maybe some windows.
You say the existing furnace is inefficient, by that do you mean that it has a big metal flue pipe and 40% of the heat goes out the flue or do you mean you think it cost more than it should to operate even thou it is a 90+ unit with plastic vent pipes? Is the second-floor duct work and or equipment in the attic?
Walta