Almost every house has a room that's never quite right. Here's why, and what you can do about it.
Why Are Some Rooms Warmer or Colder?
- Ductwork that wasn't designed carefully in the first place.
- The sun. A room that gets afternoon sun will be warmer than a shaded one.
- Distance. Rooms far from the furnace get less air.
- Floors. In summer, the basement is almost always coolest, the main floor warmer, and the top floor warmest. With a central system, some difference between floors is normal and nearly unavoidable.
What's the Difference Between Balancing and Zoning?
- Balancing means getting as much of the house as possible close to the thermostat setting. If you set 70 °F, you want most rooms at or near 70.
- Zoning means different temperatures in different parts of the house, on purpose.
How Do I Fix It? Start at the Top of This List
1. Open your vents. If more than about 10% of your vents are closed, something isn't working right, and the closed vents restrict airflow for the whole system. Open them up, even the ones in the basement. And closing the vent in one bedroom usually doesn't help the rest of the house. It mostly just starves that room.
2. Check your return air. Supply vents are your system breathing out. Return vents are it breathing in. Lots of homes have 10 or 12 supply vents but only one or two big returns per floor. Picture a bedroom with a supply vent, the return out in the hallway, and the door closed with barely a gap underneath. The air has nowhere to go. It's like trying to blow up a balloon forever: at some point, the air runs out of room. Fixes include bigger returns, or a passive return, which is a grille on each side of the wall so air can get out of the room and back to the system.
3. Manual dampers near the furnace. These are adjustable valves in the ductwork, on the main trunk line or right off the furnace, that control how much air goes down each branch. Adjusting them close to the source is far more effective than closing vents in the room. They're set once and generally left alone, and they're usually the most affordable way to rebalance a house, depending on how easy the ducts are to reach.
4. Electronic zoning. Motorized dampers plus several thermostats or sensors let you send more air to one part of the house than another. You can't heat one zone and cool another at the same time, though. Zoning is easiest with a new system or during a renovation with new ducts. Adding it to existing ductwork in a finished house can get expensive fast. Almost anything is possible, but not everything is economically feasible.
5. Mini splits. Each mini split head heats or cools its own space, so room-by-room control comes built in, without re-ducting the house. In my house, three ceiling cassette heads are controlled separately. One room holds 75 °F while an empty room sits at 60 °F and barely runs.
Should I Use My Existing Ductwork?
Most of the time, yes. If you have ducts, it usually makes sense to use them. The exception is ductwork that's far too small for a modern heat pump and air conditioning. Then a multi-head mini split system may be the better option. There's no one right answer for every house.
Zoning and Balancing FAQ
Should I Close Vents in Rooms I Don't Use?
Usually not. Closing more than about 10% of your vents restricts the whole system. Dampers near the furnace are a better way to shift airflow.
Why Is My Upstairs Always Hotter in Summer?
Heat rises, the roof takes the sun, and the upstairs is farthest from a basement furnace. Some difference is normal. Balancing, better returns, zoning or a supplemental mini split can reduce it.
Is Zoning Worth It?
In a new system or a big renovation, often. Added to existing ducts in a finished home, it can cost more than it's worth. Mini splits are sometimes the simpler route.