Ductwork
Ductwork
London Ontario
Ductwork is the invisible system that determines how much of your furnace's or heat pump's output actually reaches the rooms in your home. Leaky ducts waste 20 to 30 percent of conditioned air before it arrives. Undersized ducts cause the furnace to short-cycle on the high-limit switch and the AC coil to ice over. Kinked flex duct cuts airflow to individual rooms by 50 to 70 percent. Hawana assesses, repairs, seals, and replaces ductwork across London Ontario and Southwestern Ontario — as a standalone service or included with every new furnace and heat pump installation when needed. TSSA certified. BBB A+. 138 five-star reviews.
Leaky Ducts — The Invisible HVAC Efficiency Problem
A new high-efficiency furnace installed into a leaking duct system does not deliver its rated efficiency. The ductwork is the delivery system — and delivery system losses reduce the effectiveness of every dollar spent on heating and cooling equipment.
20 to 30 Percent of Conditioned Air Is Lost Through Typical Duct Leakage
Natural Resources Canada and the US Department of Energy both report that duct leakage in typical forced-air systems loses 20 to 30 percent of conditioned air before it reaches living spaces. In a London Ontario home spending $1,500 per year on gas heating, this represents $300 to $450 in direct annual waste — energy the furnace generates that exits into the attic, basement, or wall cavity rather than heating rooms. A 96% AFUE furnace installed into a duct system with 25% leakage delivers an effective efficiency of approximately 72% to the rooms — barely better than an 80% AFUE unit installed into tight ducts.
The new furnace with old leaky ducts problem: One of the most common scenarios Hawana encounters is a homeowner who has just installed a new 96% AFUE furnace and is disappointed that the efficiency gains did not match expectations. A ductwork assessment often reveals significant joint leakage that was pre-existing and was never addressed during the furnace replacement. Hawana includes a ductwork assessment at every new furnace and heat pump installation estimate, and includes necessary duct work in the written quote before installation begins — so the new equipment delivers its rated performance from day one.
Common Ductwork Problems — What Goes Wrong and Why
Each problem below has a different cause and a different fix. Correct diagnosis is the starting point for every duct assessment.
Leaking Joints and Seams
Sheet metal duct joints assembled without mastic, or sealed with standard duct tape that has dried and failed, allow conditioned air to escape into unconditioned spaces. Joints at the plenum box, at trunk connections, and at branch take-offs are the most common leak points. Fix: mastic sealant applied to all accessible joints and seams. Permanent fix that survives thermal cycling indefinitely.
Separated Flex Duct Connections
The inner liner of a flex duct run can separate from the collar at the take-off or register boot, particularly in basement ceilings and crawlspaces where the connection is under tension or was not properly secured with a draw band. The outer jacket remains in place but the inner liner has disconnected — all air intended for that room vents into the basement or crawlspace. This is invisible without a physical inspection. Fix: reconnect inner liner, install proper draw band and foil tape.
Kinked or Compressed Flex Duct
Flex duct that is kinked at a joist crossing, over-extended and sagging, or compressed by storage items restricts airflow severely. A flex duct kinked to a 90-degree bend can reduce airflow by more than 50 percent. Fix: straighten and re-route the flex duct with proper support at the required radius. This is one of the most common causes of a single room being consistently colder than the rest of the home — as Lark T.'s review below describes.
Undersized Ductwork
Ductwork designed for an older, smaller furnace may be undersized for a replacement unit with higher airflow requirements. Insufficient airflow causes the furnace high-limit switch to trip (the heat exchanger overheats) and causes the AC evaporator coil to ice over. Static pressure testing quantifies the restriction. Fix: add supply or return air duct capacity. Return air is the most commonly undersized element in London Ontario duct systems.
Uninsulated Ducts in Unconditioned Spaces
Ducts running through uninsulated attics, crawlspaces, or cold basements lose conditioned air temperature to the surrounding unconditioned space — even if the duct is well-sealed. A duct carrying 60°C supply air through an uninsulated attic in a London Ontario January loses a significant portion of that heat before the air reaches the register. Fix: wrap duct with appropriate duct insulation.
Duct Sealing Methods — Mastic, Foil Tape, and Aeroseal
The duct tape sold at hardware stores is not a duct sealing material. Its adhesive fails within 3 to 5 years under the temperature cycling of an HVAC system. Here are the methods that actually work.
Mastic Sealant
A water-based paste brushed or gloved onto duct joints and seams. Cures flexible and remains permanently sealed through thousands of thermal expansion and contraction cycles. Does not dry and crack like tape adhesive. The professional standard for accessible duct sealing. Hawana uses mastic on all sheet metal joint sealing work.
UL-Listed Foil Tape
Aluminium foil-backed tape with a pressure-sensitive adhesive rated for HVAC applications. UL 181-listed foil tape bonds properly to clean metal and holds through temperature cycling. Suitable for flex duct connections and as a supplement to mastic on sheet metal. Not the same as the silver cloth-backed duct tape sold in hardware stores — which should not be used.
Aeroseal
A proprietary process that pressurises the duct system and injects aerosolised sealant particles that adhere to leak edges from inside the duct. Effective for sealing leaks in inaccessible locations — inside walls, under slabs, in finished ceilings. Higher cost than mastic sealing. Most London Ontario homes with accessible ductwork do not require Aeroseal — mastic and foil tape are sufficient.
Standard Duct Tape (Fabric)
Despite the name, standard fabric-backed duct tape is not suitable for HVAC duct sealing. Its adhesive dries and fails within 3 to 5 years under the temperature and humidity cycling of an active duct system. Many London Ontario homes have ductwork sealed with this tape that has been failed for years without the homeowner knowing. If your ductwork has standard duct tape on the joints, it is no longer sealed.
Flex Duct vs Sheet Metal — The Right Material for Each Application
Most London Ontario homes use a hybrid system — sheet metal for trunk lines and branches, flex duct for final runs to registers. Each material has its appropriate applications and its failure modes.
🔌 Flex Duct — Where It Belongs
- Short final runs (2 to 3 metres) from branch to register boot
- Situations where running sheet metal is impractical (tight spaces)
- Requires proper support every 1.2 metres — no sag allowed
- Requires minimum bend radius — no kinking at joist crossings
- Inner liner must be secured to collar with draw band AND foil tape
- Must be pulled fully extended — never compressed or folded
- Not appropriate for long runs over 3 to 4 metres
- Service life approximately 15–25 years
🔌 Sheet Metal — Where It Belongs
- Main supply trunk lines from the furnace/air handler
- Return air ductwork
- Long branch runs over 3 metres
- High-velocity applications requiring low resistance
- All joints and seams must be sealed with mastic (not duct tape)
- Lasts the life of the building when properly sealed and protected
- Higher material and labour cost than flex duct
- Required when ducted heat pump or AC is installed for first time
The flex duct problems Hawana finds most often: Over-extended sagging runs in unfinished basements; kinked runs at joist crossings where the installer did not account for the bend radius; inner liners that separated from the collar because a draw band was never installed; and flex duct used for long trunk runs where sheet metal should have been used. All of these reduce airflow to the rooms those runs serve and are straightforward to diagnose and correct.
Signs of Ductwork Problems in London Ontario Homes
Most ductwork problems are invisible without a physical inspection. These are the symptoms that indicate an assessment is warranted.
Rooms That Are Consistently Too Cold or Too Hot
One or two rooms that cannot reach thermostat setpoint despite the rest of the home being comfortable indicates restricted or separated airflow to those registers. Kinked flex duct, separated connections, or a closed/partially closed damper.
Higher-Than-Expected Gas Bills
If your gas heating bills are higher than comparable homes of similar size and insulation, duct leakage is one possible cause. A 25% duct leakage rate adds approximately $375 to a $1,500 annual heating bill.
Excessive Dust Near Registers
Ducts that pass through dusty attics or crawlspaces and have leaks can draw unconditioned, dust-laden air into the duct system and deliver it to rooms. Registers that accumulate dust faster than expected may indicate duct leakage pulling in external air.
Furnace Short-Cycling or Tripping the High-Limit
A furnace that fires and shuts off repeatedly without completing a full heating cycle may be tripping the high-limit switch due to insufficient airflow — which can result from undersized ductwork, a clogged filter, or blocked supply registers. Check the filter first.
Musty Smell from Registers When Furnace Runs
A musty or earthy smell from supply registers when the furnace starts can indicate ductwork that passes through a damp basement or crawlspace and has leaks drawing in that air. A duct inspection identifies the leak location.
Old Home with Original Ductwork
London Ontario homes built before 1990 often have original duct systems with friction-fit joints, no mastic, and original duct tape that has failed. Pre-1990 ductwork should be assessed before any new HVAC equipment is installed.
Your HVAC Ductwork Specialist — London Ontario
Abdullah Ghzail — Lead HVAC Technician & Founder
Abdullah assesses and repairs ductwork across London Ontario and Southwestern Ontario since 2018 — a ductwork assessment at every new furnace or heat pump installation because a 96% AFUE furnace installed into a duct system losing 25% of conditioned air is not a 96% AFUE furnace to the homeowner; mastic sealing rather than duct tape because mastic lasts permanently and duct tape does not; and honest assessment like Reed B.'s below where the ductwork was found to be in good condition and no upsell occurred. TSSA certified. BBB A+. 138 five-star reviews.
Ductwork Reviews — London Ontario
138 five-star reviews — separated flex duct and undersized return found at furnace install (Hyde Park), kinked flex causing cold back bedroom solved (Lark T.), honest assessment found ductwork was fine before AC added (Reed B.). Read all ↗
"Had Hawana install a new Carrier 96% AFUE at our Hyde Park London home. At the estimate visit, the technician did a walk-through of the existing ductwork and identified three issues: a partially separated flex duct in the basement, two sheet metal joints with no mastic leaking, and an undersized return air duct. All three were included in the installation quote — sealed, repaired, and the return extended — so the new furnace was delivering into a properly sealed system from day one. First heating season: noticeably more even temperatures throughout."
"Our back bedroom has been cold every winter for years — thermostat at 21 degrees in the living areas but the back bedroom barely 18. Hawana traced the supply duct and found the flex duct run was severely kinked at a joist crossing in the basement ceiling — cutting airflow by an estimated 60 to 70 percent. The damper on that branch was also partially closed from a previous attempt to balance the system. Flex duct straightened, damper balanced. The back bedroom now reaches the same temperature as the rest of the house. A diagnosis that had been missed for years."
"Asked Hawana to assess our ductwork before adding central AC. They found the existing sheet metal trunk and branch system was in good condition — properly sized, well-sealed at most joints — but the original duct tape on four joints had dried and was no longer sealing. Mastic applied to those joints. The assessment also confirmed the ductwork was sized adequately for AC without modification. Central AC installed same visit. Clear, honest assessment with no attempt to oversell duct work that was not needed."
Ductwork Service — Southwestern Ontario
Same standards across the entire service area. No travel surcharge.
Ductwork FAQ — London Ontario 2026
Energy loss from duct leakage, causes of duct problems, sealing methods, flex vs sheet metal, signs of ductwork failure, balancing, lifespan, and duct cleaning vs sealing.
Ductwork Assessment in London Ontario?
Leaky ducts waste 20 to 30 percent of your furnace output. Hawana assesses, seals, and repairs ductwork as part of every new furnace or heat pump installation — and as a standalone service for homes with uneven temperatures, high bills, or aging duct systems. TSSA certified. BBB A+. 138 five-star reviews.
More HVAC Services — London Ontario
🔥 Furnace Services — From $3,400
Repair, install, maintain. Ductwork assessed at every new install. 24/7.
🔥 Furnace Installation — From $3,400
Goodman, Carrier, Lennox. Ductwork included in quote when needed.
🌡️ Heat Pumps — HRS Rebate up to $7,500
Cold-climate ASHP. Duct sizing assessed for heat pump compatibility.
❄️ Air Conditioning — From $3,500
Central AC. Duct capacity confirmed before installation.
💨 HRV — Heat Recovery Ventilator
Fresh air ventilation integrated with duct system. London Ontario.
💇 Gas Line Services
TSSA certified. Gas line work for new furnace installations.