HVAC system types, sizing, permits and maintenance
Sized to the house, not to the catalog. The tonnage on the quote matters more than the badge on the box.
How a heating and cooling system works, and when to replace it
A central system moves heat rather than making air: a furnace or a heat pump adds it in winter, a condenser or the same heat pump pulls it out in summer, and the ducts carry the air between. Replacement is due when a condenser passes twelve to eighteen years or a furnace fifteen to twenty, when repairs start to repeat, or when the house never held temperature in the first place.
Capacity is counted in tons, one ton being 12,000 BTU per hour of cooling, and most houses need two to four. That figure comes from a load calculation, usually Manual J, which accounts for insulation, glazing, orientation and air sealing. The label on the unit being removed is no guide: older systems were very often installed a size too large.
A replacement runs in a set order. The contractor sizes the house, inspects the ductwork, pulls the permit, recovers the old refrigerant as the EPA requires, sets the new equipment and line set, then commissions it by measuring airflow and static pressure and weighing in the charge. A quote that skips one of those steps is describing a shorter job.
Furnace and AC, heat pump, mini-split or geothermal: HVAC system types
| System | Lifespan | Best for |
|---|---|---|
| Central air conditioner | 12 – 18 years | Cooling only, tied into the furnace you already have. The cheapest way back to a working system when the heat still works. |
| Heat pump | 12 – 20 years | Heats and cools from one machine, and the only option that pays back on an electric bill. Cold-climate models now work well below freezing. |
| Furnace and AC | 15 – 20 years | The conventional pair: gas furnace for heat, separate condenser for cooling. Still the default where gas is cheap. |
| Ductless mini-split | 15 – 20 years | One outdoor unit feeding wall heads, no ducts at all. The answer for additions, converted attics and houses that never had ductwork. |
| Geothermal heat pump | 25 – 50 years | The ground loop outlives everything else on this list and costs what the drilling costs. A twenty-year decision, not a repair. |
Lifespans assume a system sized by load calculation and serviced on schedule. The geothermal figure describes the ground loop, which outlasts the heat pump connected to it.
Size the HVAC system before choosing the brand
A system one ton too large runs short cycles, wears out sooner and leaves the house humid. Oversizing is the trade’s most common mistake, and the tonnage line on the quote is where it shows
Sizing, ductwork and lifespan: HVAC replacement questions
How is a new HVAC system sized?
By a Manual J load calculation on the house itself: wall and attic insulation, window area and orientation, air leakage and the local design temperatures. Square footage alone, or the tonnage printed on the old condenser, is a shortcut that usually lands a size too big.
Should I replace a furnace and AC with a heat pump?
In most of the country it is now the default choice. One machine covers heating and cooling, and cold-climate models keep working well below freezing. Where winters are severe and gas is cheap, many owners keep a furnace as backup and pair it with a heat pump in a dual-fuel setup.
Can the existing ductwork stay with a new system?
Often, once it has been measured. Ducts that are sealed and sized for the new airflow can be reused; ducts that leak into an attic or crawl space, or that were undersized from the start, will keep any new equipment from reaching its rating.
Which efficiency rating should a new system have?
At least the federal minimum for your region, which a licensed installer has to meet anyway. Above that, higher SEER2 and HSPF2 ratings matter most in long, hot summers or long, cold winters, and variable-speed equipment also handles humidity better than single-stage units.
How long does an HVAC system last?
A central air conditioner lasts twelve to eighteen years, a gas furnace fifteen to twenty, a ductless mini-split fifteen to twenty, and a geothermal ground loop twenty-five to fifty. Correct sizing and regular service move those figures more than the brand on the cabinet.
Does replacing an HVAC system need a permit?
In most jurisdictions, yes. The permit triggers an inspection of the gas, electrical and refrigerant connections, and in many places it is what puts the load calculation on paper. An installer who offers to skip it is skipping the only independent check on the work.
What maintenance keeps a heat pump or furnace running?
Change or clean the filter every one to three months, keep two feet of clearance around the outdoor unit, and keep the condensate drain clear. A technician should check the refrigerant charge, the coils and the electrical connections once a year, before the season the system works hardest.
How do I choose an HVAC contractor?
Look for a state license, proof of insurance and EPA 608 certification for refrigerant handling. Then judge the visit: a serious contractor runs a load calculation, looks at the ductwork from inside the attic or basement, names exact model numbers, and explains how the system will be commissioned.
The calculator prices systems per ton on the same national data as every guide on this page; no phone number, no lead form.
Size it first Before the first quote