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A contractor quoting a furnace installation in Merrimack County has to size the equipment against a heating load that runs hard through most of the calendar before they can settle on a model or a configuration. Homes in Merrimack County, NH run heat about nine months a year, from September through May. The burner, heat exchanger, and ignition system cycle through that span with almost no idle time to recover, so a unit that is marginally sized or loosely commissioned accumulates wear on those components faster than it would in a shorter season. Getting the load calculation right before the install is what decides whether the equipment holds up through its expected service life.
Ductwork laid in for an older system does not automatically carry a new one. The trunk sizes, branch runs, and return paths that made sense for what was originally installed can restrict airflow for a modern furnace, and a contractor has to trace that layout before anything else on the job is priced. Half the homes in Merrimack County, New Hampshire were built in 1977 or earlier (2020-2024 ACS 5-year). That share of the county's housing stock means a meaningful portion of installations here turn on what the existing duct system will and will not pass, and on whether the electrical service at the panel matches what a new unit draws.
What Gets Installed With a New Furnace
The furnace itself sits in a mechanical room, basement, or utility closet, and it is the unit that produces heat for the house. A contractor mounts the flue pipe to it, running the exhaust up through the wall or roof to carry combustion gases out of the living space. Those two pieces are the core of what goes in.
The air handler or blower cabinet connects to the furnace and pushes conditioned air into the duct system. A thermostat goes on an interior wall and gives the homeowner a point of control over the whole system. The contractor also installs a filter housing where the return air enters, keeping the equipment clean from the first day it runs.
The drawing shows a typical layout, and a licensed contractor determines exactly what applies to your house and how each piece fits into it.
Find a contractor in Merrimack CountyMerrimack County, by the numbers
138 severe weather events were recorded in Merrimack County, New Hampshire 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 Merrimack County, New Hampshire were built in 1977 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesMerrimack County, New Hampshire holds 66,497 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 73.5% of the occupied homes in Merrimack County, New Hampshire (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesFurnace & HVAC Installation Rules for Merrimack County, New Hampshire6 sourced standards & codes
What furnace installation looks like in Merrimack County
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 Merrimack County, New Hampshire
New Hampshire's mechanical licensing board issues nine credentials — hearth system, four fuel gas endorsements, domestic appliance technician, and master, journeyman and apprentice plumber — and a licensee may not work outside the specialty their licence names. None of the nine is an HVAC licence.
New Hampshire does not license HVAC as a trade, and says so where it matters: the plumbing licence expressly does not reach a person installing heating, cooling, air conditioning or domestic water heating systems, whether solar, oil, gas or electric. The gas piping on a gas-fired system is a separate matter and needs a fuel gas fitter licence.
Severe Weather Events in Merrimack County
New Hampshire winters put real load on heating equipment, and how hard a system works over its life depends on what the local climate actually delivers. That workload shapes which equipment belongs in a home and how it should be sized and installed.
138 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.