HVAC guides for homeowners

Plain-English answers on heating and cooling: fixing, choosing, sizing and looking after a system – independent of any HVAC company or brand.

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Heat or AC out right now? Start with the emergency guide. Buying a system? Read repair or replace and sizing before you compare quotes. Looking after one? Start with the seasonal checklist and filter guide. Stuck on a word? The glossary explains it.

Something is wrong right now

HVAC emergency: no heat or no coolingSafety first: when to leave, what to check, what to tell the company.AC not cooling? 10 checks before you callMost "no cooling" calls start with something you can check in ten minutes. Here is what to look at, in order, and when to stop and call.Furnace not working? What to check firstA furnace that will not start is often stopped by a safety switch doing its job. Here is how to find which one – and when to leave the house instead.

Heating season: problems and prevention

Furnace smells like burning? What the smell means and what to doMost furnaces give off a faint smell the first time they run each fall. A few smells mean turn the system off now, and one means get out of the house. Here is how to tell them apart.Heat pump blowing cold air? Normal behavior vs a real problemA heat pump can feel like it is blowing cold air when it is working normally. It can also mean a real fault. These checks help you tell which one you have.Furnace short cycling: why it turns on and off so oftenA furnace that runs for a few minutes, shuts off and starts again over and over is short cycling. It wastes energy, wears out parts and leaves rooms uneven. Here is what causes it and what you can check.Furnace making noise? What each sound usually meansFurnaces make some sound when they run. New or louder noises are often the first sign of a problem. This guide matches each sound to its usual cause and tells you which ones to act on now.How to prevent frozen pipes: before and during a freezeWater expands as it freezes, and that pressure can split a pipe. A few steps before winter and during cold snaps prevent most frozen pipes, and the right response limits damage when one freezes anyway.Space heater safety: the rules to follow every timeSpace heaters are handy in a cold room or during a heating breakdown, but they cause a share of home fires out of proportion to how often they are used. A few rules prevent most of the danger.How to winterize an AC unit (and when not to)An outdoor air conditioner needs little care over winter, but a few steps in fall keep it clean and ready for spring. First, make sure it really is an AC and not a heat pump.

Choosing and buying

Repair or replace your HVAC system? How to decideWhen a technician says "you need a new system", it may be true – or it may not. Here is how to weigh it yourself.Heat pumps explained: how they work and when they fitA heat pump is one machine that heats and cools by moving heat instead of making it. Here is how it works, what it is like to live with, and how to tell if it suits your home.Geothermal heating and cooling: how it works, costs and whether it fitsGeothermal systems heat and cool a home by trading heat with the ground instead of the outdoor air. They cost more to install and last a long time. Here is how they work and how to judge whether one suits your home.HVAC sizing: why a load calculation mattersBigger is not better. A correctly sized system is quieter, more comfortable and longer-lasting. Here is how proper sizing works and what to ask for.HVAC efficiency ratings: SEER2, EER2, HSPF2 and AFUEEvery quote is full of ratings. Here is what each one measures, what the federal minimums are, and how much the number should matter in your decision.How to hire an HVAC companyEight questions to ask, and how to spot a call-center site.

Maintenance and care

HVAC maintenance checklist: what to do each seasonA few minutes a month and one professional visit a year prevent most breakdowns. Here is the checklist, season by season.How often to change your air filter (furnace and AC)There is no single schedule that fits every home. The habit that works is to look at the filter every month and replace it when it is dirty. Here is what speeds that up and how to get the swap right.AC maintenance: a spring checklist for homeownersA central air conditioner needs a little attention before the first hot week. Most of it is cleaning and clearing you can do yourself in an afternoon; refrigerant and electrical work belongs to a technician.Furnace maintenance: a fall checklist for safe heatA gas furnace burns fuel inside your home, so fall maintenance is about safety as much as comfort. Here is what to do yourself and what the yearly professional inspection should cover.Heat pump maintenance: year-round care in both seasonsA heat pump heats in winter and cools in summer, so it runs more of the year than an AC or a furnace alone. Simple upkeep matters in every season, especially keeping the outdoor unit clear of snow and ice.Mini-split maintenance: cleaning filters, heads and drainsDuctless mini-splits have no ducts to hide dust in. Each indoor head has its own filter, coil and fan, and a few minutes of cleaning keeps them quiet, efficient and fresh-smelling.Duct cleaning and duct sealing: what helps and what to skipAir duct cleaning is sold hard, but the EPA recommends it only in specific cases. Sealing leaky ducts is a less talked-about job that often does more for comfort and energy bills.Thermostat settings that save energy without sacrificing comfortYour thermostat controls most of what you spend on heating and cooling. A few setting habits save energy without making the house uncomfortable.Indoor humidity: the right level and how to control itHumidity affects comfort, your home and mold growth as much as temperature does. Here is the level to aim for and the tools that control it.

Safety and reference

Carbon monoxide and your furnace: alarms, warning signs and what to doCarbon monoxide is a poisonous gas you cannot see or smell. Fuel-burning furnaces, boilers and water heaters can produce it when something goes wrong. Alarms and yearly inspections are the main defenses.HVAC refrigerant changes: R-22, R-410A and the new A2L refrigerantsThe refrigerant inside air conditioners and heat pumps has changed twice in a generation. Here is what that means if your system is old, new, or about to be replaced.HVAC glossaryOver a hundred heating and cooling terms in plain English.HVAC licenses by stateWho licenses HVAC work in every state, with the official lookups.

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Our guides are written for homeowners, without prices that go stale or brand recommendations. Editorial policy.