# Buying Guides These guides explain how to choose, not just what to buy. Each one starts with the selection criteria and trade-offs, then points to matching options if you want them. _Last updated: 2026-09-28_ ## Articles - [Best Air Purifier Size for a Bedroom](https://www.smartairguide.com/guides/best-air-purifier-size-for-a-bedroom/) — Size a bedroom air purifier correctly using smoke CADR and air changes per hour, with a worked example and the mistakes to avoid. - [How to Choose a Dehumidifier for a Basement](https://www.smartairguide.com/guides/how-to-choose-a-dehumidifier-for-a-basement/) — Choose a basement dehumidifier by capacity, dampness, temperature and drainage, with a sizing table and the features that actually matter. - [How to Choose a Space Heater for a Bedroom](https://www.smartairguide.com/guides/how-to-choose-a-space-heater-for-a-bedroom/) — Size a bedroom space heater by watts, choose the right type for quiet or fast heat, and understand the safety and running-cost basics. - [Portable AC BTU: ASHRAE vs DOE Explained](https://www.smartairguide.com/guides/portable-ac-btu-ashrae-vs-doe/) — Why the same portable AC has two BTU numbers, which one to use for sizing, and how to match capacity to a room. - [Tower Fan vs Pedestal Fan for a Bedroom](https://www.smartairguide.com/guides/tower-fan-vs-pedestal-fan-for-a-bedroom/) — How tower, pedestal and ceiling fans differ on airflow, noise, footprint and placement, and which one fits a bedroom. ## What you will find here - Sizing and capacity guides (CADR, BTU, pints) - Choosing between product types for a scenario - Understanding certifications and labels - How to compare running and filter costs ## Frequently asked questions **Q: Do you only recommend DREO products?** A: Our guides are written around generic selection criteria so you can compare any brand. Where we link to specific products they are examples that meet the criteria, and those links may be affiliate links. --- Canonical: