Heat pump or furnace for a St. Augustine winter that lasts about four frosts

Side by side on a 40-degree morning in Fullerwood Park

Two bungalows, same street, same January dawn. One has a heat pump: the outdoor unit runs, the registers blow air that is warm rather than hot, and the house climbs from 62 to 68 over forty minutes on a modest draw from FPL. The other has a gas furnace: the burner lights, the air arrives noticeably hotter, the house is at 68 in fifteen minutes, and the meter that moved was the Peoples Gas one.

By nine o’clock the sun is on both porches and neither system is running. That is the St. Augustine heating season in miniature. The furnace wins the sprint on a cold morning and then sits idle for the next nine months while the heat pump next door does the heavy lifting of August. Which one you want depends on how much that sprint is worth to you and whether gas is already at the house.

Start with the warranty and the service schedule, not the burner

Furnaces here run so few hours that the usual way of thinking about them, efficiency rating first, is nearly backwards. A furnace that runs 150 hours a year cannot pay back a premium efficiency tier in any reasonable time. What matters instead is how long the heat exchanger is warranted, whether the parts warranty requires registration and annual service, and who is going to do that service.

Lennox furnaces carry a limited parts warranty and a longer heat exchanger warranty; the terms depend on the tier and on registering the unit after install, which we do for you. Read those terms before the brochure. A heat exchanger warranty is the one that matters, because a cracked exchanger is the one failure that makes a furnace unsafe rather than just broken.

Why idle equipment needs a yearly visit anyway

The furnace that fails on the first cold call of December did not break in December. It sat through a humid summer in a garage or attic, gathering corrosion on the exchanger, dust and insects in the burner, and a weakened igniter nobody tested. A pre-season visit in November lights it, checks the flame, measures carbon monoxide at the registers, and confirms the vent is clear. That visit is also what keeps the warranty valid on most tiers. Skip it for a few years and the first sign of trouble is a safety switch locking the unit out on the one December dawn you need it.

Book a November furnace check

The St. Augustine households a furnace still suits

• Houses with an existing Peoples Gas line, where the gas is already paying for itself on water heating and cooking.
• Large, drafty historic homes in the Model Land District or Abbott Tract with plaster walls and high ceilings, where a heat pump’s gentler output struggles to catch up on a frosty morning.
• Households with someone who feels the cold acutely and wants heat fast.
• Buyers choosing a dual-fuel setup: a heat pump for the mild days, the furnace only below a set outdoor temperature.
• Commercial spaces along San Marco Avenue or US 1 that already have gas service.

Who should not

Most of the market. All-electric subdivisions in World Golf Village, Murabella and Palencia have no gas and no reason to add it. Condos at the beach cannot vent one. Historic frame houses without ducts are better served by ductless heat pumps that also cool. And anybody buying a furnace because the house feels damp is solving the wrong problem. A heat pump with electric strips as backup covers four or five frosts a year without a gas line, a flue, or a second utility bill.

What we quote when a furnace does make sense

One stage, two stages or modulating, matched to the cooling coil that sits on top of it, sized from the house and not the old nameplate, vented correctly, and with the registration and the first November service built in. We also tell you plainly when the heat pump quote next to it is the better buy, which in this town it often is.