Conflicting contractor estimates complicated a Massachusetts homeowner's plans to replace two gas furnaces that were more than 30 years old with heat pumps.
Here's what to know
In a Reddit post, the homeowner shared three Manual J reports, which calculate how much heating and cooling a home requires.
The cooling estimates ranged from 45,901 to 65,649 British thermal units per hour, or BTUH, while the heating estimates ranged from 63,000 to 80,062.
The two-furnace, two-heat-pump choice would be sized for 60,853 BTUH for cooling and 80,062 for heating, labeled as Option C. Alternatively, the homeowner could pair one furnace with a large heat pump sized for Option B, which needed 45,901 BTUH for cooling and 75,701 for heating.
"How do we decide?" the original poster asked.
A home's orientation, window placement, and attic insulation all affect the calculations. One commenter suggested that differences in contractors' measurements and software defaults could explain the disagreement.
For homeowners navigating comparisons like this, Palmetto helps you compare efficient HVAC and heat pump solutions and can connect you with vetted installers through its Comfort Plan network.
More background
Above a selected outdoor switchover temperature, a dual-fuel system uses the heat pump; in colder conditions, the furnace comes into service, a commenter explained. Neither proposed configuration would eliminate gas heat.
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For discussions with contractors, a commenter highlighted one figure to request: the heat pump's heating capacity at that switchover temperature.
The same commenter noted that the cooling estimates differed by nearly two tons of capacity and warned that oversized equipment can run in short cycles.
Summer clamminess can result when the equipment has too little running time to remove humidity from the air.
An open layout can favor a single system because it costs less to install and maintain, according to the commenter. Floors with different temperature needs, by contrast, may be better served by two systems.
What can be done?
Commenters advised including duct conditions and air leakage in the report comparison, along with insulation and local design temperatures.
Several commenters suggested the home's historical gas consumption could help check the heating estimates. QuitCarbon also shared its directory of electrification assistance programs that includes resources for Massachusetts residents.
For shoppers weighing upfront and ongoing expenses, Palmetto's Comfort Plan offers $0-down options and can deliver potential heating and cooling cost reductions of up to 50%. It also includes 12 years of free maintenance.
Pairing efficient electric HVAC with solar can further help manage utility spending and make a home more self-reliant. EasyHome offers a solar comparison-shopping tool to give homeowners multiple installation offers and make sure they get the best deal.
Where can I learn more?
Other homeowners have run into the same problem: contractors recommending different system sizes for the same home.
• A Colorado homeowner received conflicting heat pump quotes ranging from 2.5 to 4 tons.
• In the U.K., heat pump sizing estimates ranged from 2.9 to 6 kilowatts.
• An Ontario homeowner faced a bigger grant dilemma: the incentive could mean an oversized heat pump.
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