Every house seems to have one. The room over the garage. The bedroom at the end of the hall. The bonus room someone finished in 2004. The rest of the house is fine and that room is five degrees colder, and somebody in the family has been complaining about it for years.
The good news: it is almost never the furnace. The bad news: buying a bigger one will not fix it. Here is how to find the real cause.
A room with a lot of glass, three outside walls, or a floor over a garage needs more heat than its size suggests. If the duct to it was sized by rule of thumb, it is short from day one.
Air cannot go into a room that it cannot leave. A bedroom with the door closed and no return, no transfer grille and a tight door gets very little supply air. It is the most common cause we see.
Ducts running through a garage ceiling, an attic, or an outside wall lose heat before they get to the room. Leaky joints make it worse.
Rooms over garages and bonus rooms over porches often have poor insulation and worse air sealing in the floor. Cold air moves right through. No amount of heat fixes a draft.
The farthest room from the furnace gets what is left. If the duct design never accounted for that, it shows up there first.
The thermostat is satisfied in the hallway, so the system shuts off while the back room is still cold. An oversized furnace makes this worse, because it shuts off even sooner.
This one gets its own section because it is the champion of cold rooms. The floor sits over an unheated garage. The duct to it often runs through the garage ceiling. It is usually at the end of the longest run. And it often has the most windows.
Fix it in this order. First the floor: insulation that actually fills the joist space, and air sealing so garage air is not blowing up under the subfloor. Second the duct: insulated, sealed, and big enough for what the room needs. Third, if it is still short, a dedicated zone or a ductless head for that room.
Do it the other way around and you are pumping more heat into a room with a draft in the floor. Like heating a house with the door open.
If your garage door seals are shot and the garage drops well below freezing, the room above feels it. A warmer garage helps the room above it more than people expect.
Is the damper open? Is the register blocked by a bed or a rug? Is anything coming out? You would be surprised how often this is the answer.
Undercut the door or add a transfer grille or jumper duct. Cheap, and often the biggest single fix.
Partly close dampers to rooms that are too warm to push more air to the cold one. Small moves. Keep checking.
Especially any run through a garage, attic or outside wall. Foil tape, mastic and insulation sleeve.
Floor over the garage, knee walls in a bonus room, old windows. Fix the leak before you add heat.
A zone, a ductless head, or electric radiant in the floor. When the room needs more than the system can send, give it its own.
A room-by-room CSA F280 gives you the heat that room needs on the coldest day, in BTUs, and from that the airflow. Measure what is actually coming out of the register and compare.
If the room needs 4,000 BTU an hour and the duct can only deliver half that, you have a duct problem. If the duct delivers plenty and the room is still cold, you have a draft or an insulation problem. The number tells you where to spend money, so you only spend it once.
Planning a renovation or an addition anyway? That is the cheapest time to fix it, because the walls are open. See heat loss for renovations.
Tired of the cold room? A room-by-room heat loss shows what it needs. Then you fix it once.
Get Free Quote →Three walls of it are fine and the floor is not. The floor sits over an unheated garage, the duct to it often runs through the cold garage ceiling, and it is usually at the end of the longest run. Fix the floor insulation and air sealing first, then the duct.
A little, sometimes. But closing a lot of vents raises the pressure on the system and can make it noisy and less efficient. It is a band-aid, not a fix.
Almost never. A bigger furnace makes the warm rooms hotter and the cold room stays cold, because the problem is getting the heat to that room, not making more of it. It also short-cycles.
It can make the room bearable, but you are paying electric resistance prices to cover up a design problem. Fine for a week. Expensive for ten winters.
It tells you how much heat that room needs on the coldest day, and how much air has to get to it. Compare that to what actually comes out of the register and you know whether it is a supply problem, a return problem, or an envelope problem.
For one problem room, often yes. Bonus rooms and rooms over garages are classic cases. It is cheaper than rebuilding ducts, and it gives you a separate control for that room.
Send us your floor plan or a sketch with room sizes. We calculate the heat each room needs and the airflow to deliver it, so you can see exactly where the cold room falls short.