Cross-category answers to the buying questions homeowners ask most: what it costs to run, whether it's worth buying, and which type to choose. Each links to a full, sourced answer — see How We Rank.
What size space heater do I need for a 200 sq ft room? How much does it cost to run a space heater for a month? What is the difference between a fan heater and a radiant heater? Are patio heaters worth it for a small backyard? Is it cheaper to run a space heater or central heat? Do wall heaters need to be professionally installed? What size air conditioner do I need for a 300 sq ft bedroom? Do portable air conditioners really need to vent outside? How much does it cost to run a window AC all summer? How many BTUs do I need to cool a 500 sq ft space? Is a tower fan or a pedestal fan better for a bedroom? How much electricity does a portable AC use per hour? What’s the difference between a mini-split and a window AC? Is it cheaper to run a fan or an air conditioner? Do I need a permit to install a mini-split system? What size air purifier do I need for a 500 sq ft room? Do car air purifiers make a noticeable difference in a small cabin? How much does it cost to replace filters every year? What’s the difference between activated carbon and HEPA filtration? How do I know when my HEPA filter needs replacing? Are cheaper generic filters as good as brand-name replacements? Is it worth buying an air purifier for a single allergy season? How do I know if I need a humidifier or a dehumidifier? What size dehumidifier do I need for a basement? What pint rating dehumidifier do I need for a damp crawl space? Is warm mist or cool mist better for a baby’s room? How much does it cost to run a dehumidifier all summer? What’s the difference between an ultrasonic and evaporative humidifier? Is bottled or distilled water better for a humidifier? How much money can a smart thermostat actually save per year? What’s the difference between a programmable and a smart thermostat? Is Ecobee or Nest better for a multi-zone house? Do CO2 monitors need to be recalibrated over time? Do hygrometers need batteries replaced often? How many smart vents does a typical house need?