Green Building Advisor recently tackled this very issue, examining the situation of one of their readers, Christian Rodriguez. Upgrading an 1880's home, Rodriguez found himself in a position many of us can empathize with: a plethora of needed projects, and limited time and financial resources to employ. With only so much he could accomplish, the question was clear: What could he do that would produce the maximum benefit for his effort and expenditure?
Rodriguez's first step was to commission an energy audit, a series of tests designed to reveal moisture flow, combustion safety, thermal comfort, indoor air quality, and durability factors within his home. Once that data was established, Rodriguez's next move was to seal his attic, before adding 20 inches of cellulose insulation.
It was at this point that he had a decision to make. Four projects demanded attention, but his budget would only accommodate one for the season. Rodriguez had to insulate the walls of the house with dense-packed cellulose, insulate a crawl space with closed-cell spray polyurethane foam, replace four drafty original windows, and install a high-efficiency air-source heat pump.
"According to the energy assessment, our 10-year-old furnace is fairly efficient and a heat pump would strictly be to supplement and even out low winter temps," Rodriguez observed.
"We also supplement with a wood stove. Does it make more sense to invest in insulation or a heat pump?"
Several of Green Building Advisor's responses made the choice fairly clear, recommending improvements to the building's envelope before upgrading the heating system.
"I would recommend improv[ing] the envelope first before trying to fix the comfort issue through mechanicals," wrote William Heiden.
"Air-sealing and insulating the attic is a great first step. Anything that you can do to lower the heat loss will help you to reduce the size of the mechanical equipment needed to heat the home in the future."
"I would vote for insulating the above-grade walls or sealing and insulating the crawl space," senior editor Martin Holladay adds.
"Window replacement rarely makes sense, although it would probably be a good idea to install storm windows to protect any windows with single glazing."
When it comes to his windows, Rodriguez has a number of options. Several manufacturers offer high quality exterior storm windows, while others sell removable interior storm windows, which are also an easy DIY project. In a pinch, he could insulate the interior of his windows with plastic, yet as Dana Dorsett observes, the windows are well worth keeping.
"The quality of the clear grain old growth wood in 1880 vintage sashes and frames is unmatched by modern windows," Dorsett said.
"If they're salvageable, it's worth tightening them up. Putting the storm window on the exterior keeps them warmer and drier, and extends the life of the original window."
While Rodriguez's oil-burning furnace is working, it's efficiency pales in comparison to what he could achieve with an air-source heat pump.
"The cost of operation of an 87% efficiency oil furnace at the recent 5-year average fuel and electricity costs is more than 50% higher than that of a pretty-good high-efficiency ducted heat pump and more than [twice] the cost of running ductless heat pumps," Dorsett noted.
While a laundry list of upgrades could await many of us, Rodriguez's path seems clear, according to GBA technical director Peter Yost, who asserts that Rodriguez's next steps should focus on the building envelope, particularly in the crawlspace. While he does allow that properly insulated storm windows are a solid investment, tightening the envelope and minimizing heat loss, along with effective moisture management, will directly impact heating bills, reducing the building's mechanical heating needs for the future.