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Sizing a furnace for this house is not a step a contractor can skip or estimate loosely. Homes in Montgomery County, MD run heat about seven months a year, from October through April. The burner and heat exchanger in an undersized unit cycle harder and more often to keep up, and that wear compounds across a long run. A correctly sized install, matched to the actual heat loss of the house and the length of the season, puts the system where it can handle the load without running at the edge of its capacity every cold morning.
Existing ductwork is what decides whether a furnace installation is straightforward or complicated, and in much of Montgomery County it was designed around equipment that is no longer in these houses. Half the homes in Montgomery County, Maryland were built in 1980 or earlier (2020-2024 ACS 5-year). Ductwork that served a previous system well can be the wrong size, the wrong layout, or both for what a new furnace actually needs to push through it. A contractor who prices the new unit before opening the registers and tracing the runs is skipping the part of the job where the real variables are.
What Gets Installed With a New Furnace
The furnace itself sits in the basement, utility room, or closet and is the heart of the installation. A burner inside it heats air, and a blower pushes that air through the house. The flue pipe runs from the furnace to an exterior wall or through the roof, carrying combustion gases out.
The thermostat goes on an interior wall where it reads the temperature of the living space and tells the furnace when to fire. The air handler, where it is a separate unit, sits near the furnace and works alongside it to move conditioned air. A new filter housing or media cabinet is often fitted at this stage as well.
The drawing shows the general layout of these components, and a licensed contractor determines exactly what applies to your house and how each piece gets positioned within it.
Get matched in Montgomery CountyMontgomery County, Maryland, by the numbers
541 severe weather events were recorded in Montgomery County, Maryland between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in Montgomery County, Maryland were built in 1980 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesMontgomery County, Maryland holds 406,531 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 65.3% of the occupied homes in Montgomery County, Maryland (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace Installation Rules for Montgomery County, Maryland5 codes, standards & laws
What the installation actually looks like
Non-weatherized gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized oil-fired furnaces manufactured on or after November 19, 2015 must reach 83.0 percent AFUE.
Mobile home gas furnaces manufactured on or after November 19, 2015 must reach 80.0 percent AFUE.
Non-weatherized gas furnaces manufactured on or after December 18, 2028 must reach 95.0 percent AFUE, up from the 80.0 percent minimum that applies to units manufactured before that date.
Licensing and Legal Requirements in Montgomery County, Maryland
Maryland requires a state licence before an individual provides, or assists in providing, heating, ventilation, air-conditioning or refrigeration services.
Severe Weather Events in Montgomery County
Weather puts a measurable load on heating equipment, and that load varies by where you live. A furnace sized and installed for Montgomery County's climate handles the demands this area actually places on it.
541 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.