Jennifer McEachern has finally said goodbye to the original oil-fired furnace in her 1953 Connecticut ranch, and is leaping at the opportunity improve indoor air quality as she ponders a new source of heat.
There are other issues as well, as she explains in this Q&A post, such as lots of air leaks in her home’s building envelope. A blower-door test shows 15.7 air changes per hour at a pressure difference of 50 pascals, 10 times what a conscientious builder might shoot for today.
McEachern says her first choice for a new heating system is a boiler that runs on liquid propane (LP) coupled with radiators. That makes some sense because the house already uses LP for other appliances, including a generator. At the same time, McEachern also would like to add a heat-recovery ventilator or a HEPA ventilation system with its own ductwork. In addition, someone has recommended she consider at AtmosAir ionization air purification system.
“Does anyone have any advice about this equipment and/or plan?” McEachern asks. “The heating contractors we have had look at the system just provide us with quotes for whatever we ask about and don’t provide advice (that we desperately need).”
While all of this is still up in the air , McEachern and her family are staying warm with a wood-burning fireplace insert that was installed a few years ago, along with a few heaters in the bedrooms.
Winter may have settled over New England, but McEachern is in no rush.
“We are prepared to take some time to get this right,” she says. So, what is the right answer? That’s the topic for this Q&A Spotlight.
Consider a heat pump instead
Propane is an expensive fuel for heat, says Keith Gustafson, who suggests that McEachern consider heat pumps instead. They would almost certainly be cheaper to run.
Drawing on personal experience, Duane recommends using minisplit heat pumps as backup heat. They can provide cooling as well as heat, and dehumidify the air during shoulder months.
“I’m heading in nearly an opposite direction,” Duane writes. “I’m looking to replace my older LP boilder (and radiators) to minisplits as our backup and supplemental heat next year after we get our leaky house tightened up.”
McEachern says she has considered just that, installing a heat pump and using an LP boiler as backup heat. But, she adds, indoor air quality is a “super important” part of the equation.
The problem, adds Akos, is that the house “leaks like a sieve.” Assuming the outdoor air is of good quality (that is, not near a source of pollution), “adding in fancy filtration and HRV will do nothing.” The amount of air leaking into the house would overwhelm what an HRV would provide. Even if the HRV air were filtered, it would be quickly diluted by air leaking in from the outside.
“Switching to radiant heat will also not do much for IAQ,” Akos adds. “Typical older furnace with leaky ducting in the attic is actually pretty good for improving IAQ. They tend to depressurize the house and suck in even more ‘fresh’ outside air. Properly sized and installed radiant tends to be more comfortable in older, leaky homes but that is a lot of $$ to spend for not much benefit.”
The current system is probably too big
Most HVAC contractors propose heating and cooling systems that are much too big, writes Dana Dorsett, so a good place to start is to calculate the heating load based on how much fuel is used (an article describing that process can be found here.)
“Even at CT electricity rates a right sized air-source heat pump will be less expensive to operate than an LP boiler (and a lot cheaper to install than a bunch of new radiation, be it flat panels or radiant floor),” Dorsett says.
Further, it may not be necessary to replace the existing air ducts. Some adjustments for better balanced air flow may be needed, but a wholesale replacement isn’t necessarily going to be required.
Because the old furnace was probably grossly over-sized, he says, it was running only one-third of the time even on the coldest day of the year—”not a recipe for comfort.”
“A right sized heat pump will be far more comfortable than the oil-burner,” Dorsett says. “The overall duty cycles will be much longer, and grow longer as outdoor temperatures drop. With the oil burner you were likely getting the hot-flash followed by the extended chill between cycles, whereas a properly sized heat pump will be yielding a nearly continuous summer-breeze flow at lower cfm with warm but not as hot as the fossil-burner’s output at the registers. It’s the high duty cycle that keeps it comfortable.”
Dorsett suggests McEachern read parts of a Nate Adams “House Whisperer” blog on this topic.
A variety of fixes have already been made
McEachern has already taken a number of steps to make the house more comfortable: new siding, doors, and roof, and excavation to solve a mold problem in the crawlspace.
“And,” she adds, “we plan to replace windows and attic insulation, along with insulation in the rim joists. We had a HERS rater come out and his recommendations should come shortly.”
But, she adds, two heating contractors have told her that an air-source heat pump wouldn’t be enough to heat the house without a supplemental heat source for the coldest days.
“I think it will, especially with electric strip backup and our very efficient (and warm!) wood-burning insert,” she says. “All of the articles and Q&As I have read on this site state exactly that, along with the fact that we are living comfortably with little heat right now.”
That’s not a surprise, Dorsett adds. “I’ve usually had to spec the equipment myself and push back on contractors when they say it’s not enough or won’t work. They’re all too nervous about undersizing (human nature), when it’s in your interest to be more concerned about oversizing.”
Heat pump will mean more even heat
BFW577, who also lives in Connecticut, says a minisplit heat pump system will provide much more even heat—and he offers his own house as proof.
“I switched from my minisplits to oil heat around 8 a.m.,” he says in reference to the graph below. “Notice the minisplit held the house at exactly 67 overnight and the large temp swings of my ridiculously oversized oil burner. It’s amazing how precise the minisplits can regulate temperature.”
BFW577 says the minisplits have been much less expensive to run than an oil-burning appliance. “Propane in CT is more expensive than oil and has far less Btus,” he adds.
Our expert weighs in
Peter Yost, GBA’s technical director, adds this:
In typical GBA fashion, knowledgeable folks have shared a ton of great information for Jennifer McEachern. I am simply going to sum up:
Use the Database of State Incentives for Renewables & Efficiency (DSIRE). This excellent and continuously updated online resource will guide you to the financial support available at both the federal and state levels. When I typed in my own zip code, 54 different programs came up for me to consider.
Prioritize your work. If you can muddle through with your current heating conglomeration for a little bit longer, or do some additional temporary heating along with heavier sweaters, follow this approach to upgrading your building enclosure before tackling your heating system:
- Manage bulk water: You need to manage moisture and energy with equal intensity or you will end up with moisture problems.
- Manage air (in this order): top (attic), bottom (especially above-grade portions of your foundation, including the rim joist), shafts and chases, and walls. This last one surprises some people, especially as it relates to windows. Replacing windows involves a lot of options (interior or exterior storms, sash replacement, full replacements) and this is never the place to start unless it’s about a bulk water management issue. For more on this, see this blog by Martin Holladay.
- Vapor: As you work on your enclosure, ask yourself whether you are maintaining drying potential and whether you evaluated household sources of moisture for management. For more on this topic, see this article.
- Thermal: It also may be surprising to some that insulation is at the end, not the beginning, of this list of performance improvements.
Now that you are down at the end of this list of improvements to your enclosure, you can go about selecting and sizing the heating system suited for the performance of your building. Dana and crew have nailed this for you in the Q&A.
Find the right contractor. Jennifer already seems to know that this may be the hardest part. While we qualify and certify energy and building performance auditors and raters, we don’t have a similar national system for those who do the actual work. I wrote a draft of “how to interview your builder” and attached it to this GBA blog: How (Older) Homes Work . I hope it helps.
-Scott Gibson is a contributing writer at Green Building Advisor and Fine Homebuilding magazine.