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Understand the numbers before you spend
An HVAC system is a five-figure, fifteen-year decision made under pressure — usually when the old one just died. These guides give you the vocabulary to make it well.
Methodology & the Verified Label Live
Where every number comes from, how we compute $/MMBtu, and what we refuse to do.
What MERV rating do I need? Live
MERV 8 vs 11 vs 13, the MERV/MPR/FPR cross-map, the airflow tradeoff, and a size chart.
Is MERV 13 too restrictive? Live
How much each brand's MERV 8, 11 and 13 slows airflow, from the makers' California filings, and who should skip MERV 13.
How often should you replace your air purifier filter? Live
The maker schedule for 20 best-selling purifiers, the genuine part, and what it costs a year.
Are off-brand air purifier filters as good? Live
Genuine vs best-selling off-brand filters for 7 purifiers: what each costs a year, what the listings claim, and what the few real tests found.
Rebadged HVAC brands: when "different" brands are the same machine Live
The biggest rebadge families in our data, computed from certified specs — plus who really owns whom, cited.
SEER2, HSPF2 & COP at 5°F, explained Live
What each rating measures, and why COP at 5°F is the cold-climate number that matters.
Will a heat pump keep up in real cold? Live
The certified COP and heating capacity at 5°F for thousands of units, mapped to your climate's design temperature. The moat question, answered with data.
Study: space heaters make the same heat, but claim very different room sizes Live
We checked 283 1,500-watt heaters on Amazon. Room-size claims run from 160 to 1,000 sq ft for the same heat.
How much does a space heater cost to run? Live
Cost per hour and month in every state, and what the same heat costs from a gas furnace, heat pump or mini split.
Heated blanket vs space heater Live
What one night costs with each in your state, which is safer, and the heated blankets recalled since 2023.
Hard freeze tonight? What to put on your pipes Live
The temperature that puts pipes at risk, what to do tonight, and which faucet covers, pipe sleeves and heat cables to buy.
Which condensate pump do you need? Live
Pick a pump by how high it must lift the water, with the safety switch and acid rules for furnaces.
What is the most energy-efficient space heater? Live
Why no plug-in heater beats another, and what the energy claims on Amazon heater listings really mean.
Heat pump vs. gas furnace Live
The honest running-cost, upfront-cost and comfort comparison — computed from certified data, settled by your energy prices.
When is it worth replacing a furnace? Live
The two replacement signals you can actually measure — age against a typical 20-year life, and what the efficiency gap costs you every year in fuel. Not another warning-signs list.
When is it worth replacing an air conditioner? Live
Age, the 50% and $5,000 repair rules, and what a replacement actually costs installed — before anyone quotes you.
When is it worth replacing a heat pump? Live
What an ageing low-HSPF2 system costs to run against a current replacement, computed from certified efficiency.
Is the Midea U-shaped worth it? Live
Yes, if it is the current UWT model. The 2025 recall of the QWT models, and how it compares with LG and TCL, with prices.
Is the Midea Cube dehumidifier worth it? Live
Each Cube vs Midea's regular unit at the same size: certified pints, efficiency and this week's price.
What size dehumidifier do I need? Live
ENERGY STAR size chart in certified pints, why the box number is bigger, and why a 50-pint suits most basements.
What size mini split for 500 sq ft? Live
Most 500 sq ft rooms need 12,000 BTU. The ENERGY STAR chart, when to go to 18,000, and certified 12,000 BTU units on Amazon.
Why is my upstairs so hot? Live
Why the upper floor bakes while downstairs is fine — and the fixes ranked cheapest to best, including when a ductless mini-split is the real answer. No upsell.
Most reliable HVAC brands / brands to avoid Coming soon
The distrust query, answered with data instead of ads.
R-454B, R-32 & the R-410A phase-down Coming soon
What the 2025 refrigerant transition means for what you buy.
Guides are written by Erin Rose and grounded in the same certified dataset behind the rest of the site. See our methodology.