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Residential · New Duct RunHeating Vent Installation — Adding a Duct Run
Heating vent installation — adding a duct run to a room that never had a supply — works when three things are true: the furnace has heat to spare, the trunk has pressure left where the new take-off goes, and the room has a way to send air back. We measure the first two before cutting metal. If total static pressure is already above the blower's rating, usually 0.5 inches of water column, a new run will only thin out the air to the rooms you already heat.
Capacity is checked in two places. At the furnace, we compare its output with the house's heat loss plus the new room, using a CSA F280 heat-loss calculation where the added space is large; many 1980s and 90s furnaces were oversized and have room. At the trunk, we read static pressure and look at where the duct steps down, because a take-off cut into the last metre of a reduced trunk gets whatever is left. Tapping the nearest branch instead of the trunk is the shortcut to avoid: it splits one room's air between two.
The run is sized to the room's load, not to the pipe on the truck. A 6-inch round branch carries on the order of 100 cubic feet a minute when it is short and straight, and less with every elbow and metre added. A bedroom may need one, a large family room two. The take-off gets its own damper so the new outlet can be balanced against the old ones, and any section passing through a garage ceiling, crawlspace or attic is sealed and insulated so the heat arrives.
Three kinds of room generate most of these calls. Enclosed porches and sunrooms have so much glass and so little insulation that one duct run rarely keeps up in January; we will say so and price a ductless mini-split alongside it. Basement rooms are close to the trunk and easy to feed, but the supply should come with a low return or the heat stays at the ceiling. Converted attics sit at the far end of the system, two storeys above the furnace, and need a chase through a closet for a run that long.
A supply without a return is half a circuit. Air pushed into a closed room pressurizes it, and delivery drops to a trickle soon after the door shuts. The return path can be a dedicated return air duct, a transfer grille through the wall, or a generous door undercut for a small room. If the real question is why an existing room is uncomfortable, start with why one room is colder than the rest or how to improve airflow to one room.
A new duct run is the right job when
- A room has no supply register at all: an enclosed porch, a basement bedroom, a converted attic or a new addition
- A large room was built with one outlet and needs a second at the far wall
- A basement is being finished and its only heat is whatever leaks from the ducts overhead
- A space heater runs all winter in one room while the furnace cycles normally
- Static pressure and furnace output have been measured and both have room for another outlet
How it works
Static pressure at the furnace, temperature rise across it, trunk dimensions at the proposed take-off and the room's heat loss. You get those four numbers and a plain answer on whether a run will work.
We choose the take-off point, the pipe diameter, the path between joists or through a chase, the register position on an outside wall and the return path. The price is written per run before any ceiling is opened.
Take-off and damper fitted, pipe hung and sealed with mastic, boot and register set, then airflow measured at the new outlet and at its neighbours. Larger layouts move over to ductwork installation; for a single room, request a visit.
Common questions
Can I add a vent myself by cutting into the nearest duct?
You can physically do it, and it is the most common reason we get called to a room that is still cold. The nearest duct is usually another room's branch, so the two outlets share air meant for one. A proper take-off comes off the trunk with its own damper, sized to the room it serves.
Will adding a vent weaken the heat in other rooms?
Slightly, if the system was at its limit, and not noticeably if there is spare capacity. That is why static pressure is measured first. When the reading is already high, the fix is to add return air or enlarge a trunk section before adding outlets; otherwise the blower works harder and every room receives a little less.
Can one duct run heat a sunroom or enclosed porch?
Sometimes for shoulder seasons, seldom for January. A three-season room with single glazing and an uninsulated floor loses heat faster than one branch can replace it, and the thermostat in the main house cannot see it. Sunroom heating and cooling compares a duct run with a mini-split and electric options.
How is a new run hidden in a finished house?
Through the basement where the ceiling is open, between joists where they run the right way, and up through closets or a boxed chase to reach upper floors. Where a route means opening finished drywall, we mark the exact cut before starting so your drywaller can price the patch along with the rest of the job.
Does a new vent also deliver air conditioning?
Yes. The same duct carries cooled air in summer, and cooling needs more airflow than heating for the same room, so a run sized only for heat can come up short in July. We size the branch for the larger of the two loads when the house has central air.