Heating and Cooling London Ontario Ductwork Tips for Better Airflow

Posted on 2026-06-12 20:07:47

When a home in London, Ontario struggles to stay comfortable, the culprit is often hidden behind drywall and joists. Ductwork design and condition decide whether your furnace and air conditioner can do their jobs. I have walked into countless homes where the equipment was new and efficient on paper, yet one bedroom roasted in summer while the basement felt like a walk-in cooler. The equipment took the blame, but the ducts told the real story.

Air moves only when the system creates a pressure difference and the duct system offers a low resistance path. If resistance stacks up from undersized trunks, crushed flex runs, leaky joints, or a filter that loads too quickly, airflow drops and comfort follows it down. Better airflow is not about one silver bullet, it is a series of small decisions from the furnace room to the furthest grille.

Why airflow matters here, not just in textbooks

Our climate swings. In February, the wind off the Thames River can push wind chills below minus 20 C. In July, a humid 30 C afternoon makes the upstairs feel sticky even with the thermostat set to 22. Those swings show every flaw in a duct system. A furnace that is starved for return air will overheat and short cycle in winter. An air conditioner with low airflow ices over and then floods the pan in summer.

Equipment efficiency only pays off when ducts let the blower move the air the manufacturer expects. Most systems target around 400 cubic feet per minute per ton of cooling, while furnaces are matched to deliver the static pressure and airflow on their nameplate. In real homes across the city, I see 20 to 40 percent less airflow than spec due to common issues. Correction of that airflow often delivers a bigger comfort gain than a new unit.

The bones of ductwork, London style

Many houses in London, Ontario share a few traits that matter for airflow. Older bungalows and wartime homes often rely on interior wall cavities used as return air chases. Those chases leak into basements and attics and pull in dust. Century homes tend to have add-on supply runs and poor return paths to second floors. Newer subdivisions lean on long trunk-and-branch layouts with basement mechanical rooms at one corner of the house, plus finished basements that box in trunks with few access points.

Metal supply trunks with round takeoffs dominate, sometimes paired with runs of flexible duct for the last leg. There is nothing wrong with flex if it is pulled tight, supported every 1.2 to 1.5 metres, and sized one to two sizes larger than the metal equivalent to offset friction. In practice, I find flex with kinks, too many sharp bends, and four metres stuffed into a two metre path.

If you are planning furnace installation london ontario or you are tackling a basement finish, expect ductwork to be part of the conversation. You can build a great entertainment room, then lose 30 percent of airflow because the trunk was boxed so tight that balancing dampers cannot be adjusted and insulation was skipped over the new cold room.

Static pressure, velocity, and the real-world target

You do not need an engineering degree to understand two numbers that matter more than most: static pressure and velocity.

Static pressure is the resistance the blower pushes against, measured in inches of water column. Most residential blowers want to see a total external static pressure between 0.3 and 0.5 inches. I carry a digital manometer on service calls and measure before and after filters, coils, and across the furnace. If I see 0.8 inches on a system that is supposed to run at 0.5, no amount of thermostat tweaking will fix its comfort issues.

Velocity is how fast air moves in the ducts. Supply runs like 700 to 900 feet per minute, returns are happier at 300 to 500. Go much faster and you get wind noise and whistling registers. Go slower and you get dust settling, temperature stratification, and poor throw from grilles.

Designers use Manual D and lookup charts to size ducts for a target friction rate. In the field, we make judgment calls. A 10 by 8 trunk might work for a short run, but not when it stretches 12 metres with three elbows. Equivalent length matters. Every elbow adds friction equal to extra straight duct. A tight radius elbow can add the equivalent of 2 to 3 metres. I have fixed chronic hot rooms by swapping two square elbows for long radius options and trimming static pressure by 0.1 inches.

Supply and return balance, not just more supply

I have rarely seen a home that suffers because it needs more supply-only registers. The usual problem is a choked return path. Air that goes into a room must find an easy way back to the furnace. If it cannot, the room pressurizes slightly and the supply flow drops.

Bedrooms with closed doors are classic examples. You can dump 120 CFM into a kid’s room, then shut the door and leave a 10 mm undercut. That undercut passes maybe 20 to 40 CFM if the hallway is the return path. The room starves. Two solutions work well. Either add a dedicated return in the room, sized properly with a lined duct to keep noise down, or add a jump duct or transfer grille that connects the room to a hallway return. I prefer jump ducts through the ceiling in two story homes, as they keep sound transfer low and avoid cutting large grilles near baseboards.

Think of returns as the express lanes. A typical 2 ton cooling system needs around 800 CFM. If your filter rack and return drop can only pass 600 CFM without sending static pressure sky high, you will never hit comfort. Wider filters and a second return drop are simple, effective upgrades during furnace installation or furnace repair when the cabinet is already open.

Register placement and free area

Registers and grilles are the last part of the chain and often the most overlooked. A high quality grille with adequate free area can reduce pressure drop and noise. Cheap, tight louver grilles that look the same from the aisle at the home center can choke 20 to 30 percent of the flow at the same face size.

Placement matters. Supplies near exterior walls and under windows wash the cold glass in winter and help counter downdrafts. In retrofit work, I have shifted just one or two supplies to better locations and seen room temperatures even out by 1 to 2 C without any equipment change. On second floors, ceiling supplies with good throw help push air across the room and down the walls, which fights the natural tendency of hot air to pool near the ceiling in summer.

Sealing and insulating, the quiet efficiency win

Duct leakage is a tax you pay every hour your system runs. I have measured leakage in unfinished basements at 10 to 20 percent of total flow, usually through drive cleats on trunks, panned returns, and poorly sealed filter racks. That leakage pulls in basement dust, bypasses living spaces, and sends conditioned air to mechanical rooms.

Sealing with https://www.instagram.com/hometownhandc/ mastic or UL 181 foil tape on metal joints, boots, and takeoffs changes the system’s behavior right away. Foam tapes on the filter rack door stop bypass. I have sealed systems in a day or two and watched return static drop by 0.05 to 0.1 inches and rooms that were starved suddenly come alive with air.

If any ducts run through unconditioned spaces like garages, crawlspaces, or cold rooms, insulation matters too. R-8 wrap on supply trunks keeps winter heat where it belongs and stops summer condensation. In finished basements, add sound liner on return drops to cut noise if you upsize grilles.

Filters, pressure drop, and allergies without the penalty

Filters keep coils and ducts clean, but they can kneecap airflow if selected or maintained poorly. High MERV ratings catch smaller particles, which is great for allergies, but often at the cost of higher pressure drop. A 1 inch MERV 13 pleated filter can eat 0.2 inches of static even when clean. On a system that runs happily at 0.5 inches total, that is a big bite.

I prefer moving to a larger media filter, such as a 4 to 5 inch cabinet, during furnace installation. The larger surface area drops pressure to 0.05 to 0.1 inches at the same MERV rating. If a 1 inch rack is all you have, step down slightly in MERV to 8 or 11 and swap the filter more often. A good rule is to check monthly for the first season, then settle into a rhythm based on how fast it loads. Homes with pets or nearby construction sites clog filters faster than quiet cul-de-sacs.

Air conditioning and coils, a two season consideration

Cooling airflow issues show up quickly in London’s sticky July stretches. The evaporator coil above the furnace is often the biggest single pressure drop in the system. Coils matted with dust can double their pressure penalty. A coil that was mismatched to the blower cfm during a past furnace repair can hold back a new air conditioner as well.

If you are planning heating and cooling london ontario upgrades, have the contractor measure static pressure before and after the coil. Clean if needed. Match blower settings to the target 350 to 425 CFM per ton based on humidity goals. Slightly lower airflow can wring out more humidity in shoulder seasons, but go too low and you risk icing and reduced capacity. In older homes with undersized returns, I sometimes set a two stage furnace to run its blower lower during first stage heating to cut noise, then raise airflow for cooling season with a thermostat schedule.

Noise control without strangling airflow

Homeowners often close dampers or registers to quiet a room. That is understandable, but it raises system pressure and pushes more air through remaining paths, making those grilles louder. The better fix is to identify and correct the source.

Sharp elbows near the furnace cause turbulence that sounds like a roar. Swapping to long radius fittings or adding turning vanes in square elbows helps. Lining the first 1 to 2 metres of return duct with acoustic liner knocks down blower noise. Use proper balancing dampers near the trunk, not decorative register levers, so you can temper airflow without a big pressure penalty.

Zoning and the upstairs problem

Two story homes in London commonly have an upstairs that runs warm in summer and cool in winter. Zoning with motorized dampers can help, but it is not magic. A zoned system needs a blower and ductwork that can handle either zone calling by itself without sending static through the roof.

Before adding a second thermostat and dampers, I look for basic improvements. Add a dedicated return upstairs. Increase the size or number of supplies on the top floor. Seal and insulate any long attic duct runs. Balance the system so more air is biased to the upstairs during cooling season. Sometimes simple fixes solve what looks like a zoning problem.

Humidity and ventilation, the Canadian code reality

Ontario homes often include heat recovery ventilators in newer builds. HRVs pull stale air from baths and kitchens while bringing in fresh air and exchanging heat to keep energy loss reasonable. Those HRV ducts should be kept separate from the furnace supply and return or tied in with proper balancing to avoid stealing airflow from the main system.

Whole home humidifiers help winter comfort but add static pressure if installed poorly. Bypass units that use a small duct between supply and return must be sized and dampered properly or they can recirculate too much warm air, changing blower performance. Steam humidifiers add moisture without affecting duct pressure but cost more and need proper water treatment to reduce scale. Consider maintenance and water quality when you choose.

Finishing basements without choking the trunk

I see this every year. A homeowner finishes a basement, boxes in the main trunk tight to the joists, and drywallers mud over the only access to a balancing damper. Within weeks, upstairs rooms lose airflow. Leave 50 to 75 mm of clearance around trunks to allow insulation, access, and to avoid conduction cooling or heating into the soffit. If you add new supply or return grilles for the basement, do a quick load estimate so you do not steal air from upstairs. Sometimes the solution is to add a dedicated return at the foot of the stairs, which improves circulation for both levels.

Quick checks a homeowner can try safely

Hold a tissue at a return grille with the fan on. If it barely pulls, the return path is likely choked. Close a bedroom door and see if the supply flow drops noticeably at the register. If it does, add a transfer path. Listen for whistling at registers. That often means the register is too restrictive or the duct is undersized. Check the filter. If it is bowed into the rack or hard to remove, static pressure is high across it. Look at flexible ducts. If they snake and sag, support and straighten them to reduce friction.

Commissioning airflow, the steps a pro should follow

Measure total external static pressure and compare to the furnace or air handler rating. Take pressure readings across the filter and coil to find the largest pressure penalties. Use a flow hood or traverse key supplies and returns to estimate delivered CFM by room. Inspect ducts for leakage, poor fittings, kinks, and missing balancing dampers, then correct. Adjust blower speed taps or ECM profiles to hit target CFM after duct corrections.

If you bring in a contractor for furnace repair london ontario and they skip these steps, press for better testing. Many airflow problems survive part swaps and thermostat upgrades because no one measured.

Matching equipment and ducts during upgrades

Furnace installation is the best time to correct ductwork, because the system is already open. Upsizing the filter cabinet, adding a second return drop, swapping tight grilles, and replacing two elbows cost far less during an install than as a separate project later. If you are replacing a 20 year old 100,000 BTU furnace with a right-sized 60,000 BTU high efficiency model, confirm that the blower settings and duct capacity line up for both heating and cooling modes.

For air conditioners, pairing a variable speed blower with a coil sized and rated for your refrigerant matters. Modern ECM blowers are forgiving but not magic. If the duct system can only pass 700 CFM at 0.8 inches, the blower will work harder, get louder, and may still fail to deliver design cooling. A careful contractor in heating and cooling london ontario will show you static pressure readings and what will be changed in the ductwork to bring numbers into range.

Cost, payback, and what to expect

Most airflow improvements are not flashy, but they pay out steadily. Sealing a leaky return drop and filter rack can cost a few hundred dollars in labour and materials. It reduces dust, improves comfort, and often allows the thermostat setpoint to be raised slightly in summer or lowered in winter without sacrificing comfort. Adding or upsizing a return for an upstairs can run from a few hundred to over a thousand depending on finishes and routes, but it can turn a problem room into a comfortable one year round.

During a furnace installation london ontario project, budget 5 to 15 percent of the job for duct corrections if your home shows clear airflow symptoms. The payback shows up in even temperatures, quieter operation, and fewer service calls for nuisance limit trips or icing.

Duct cleaning, when it helps and when it does not

People ask about duct cleaning whenever airflow comes up. Cleaning debris out of trunks and branches can reduce dust and remove construction leftovers, but it rarely fixes airflow on its own. If you can see drywall screws, pet hair clumps, or renovation debris in boots and trunks, cleaning makes sense. If the ducts are reasonably clean but registers are noisy and rooms are uneven, look to sizing, sealing, and balancing first. I have measured static pressure before and after cleaning and seen little to no change in many homes, while a single added return dropped static by a tenth of an inch overnight.

Safety and combustion air

When you change airflow, remember you are working around combustion appliances. High efficiency furnaces that vent with PVC are sealed from the room. Mid efficiency units and natural draft water heaters are not. Do not tighten a mechanical room so much that combustion air is starved. Look for proper make-up air provisions and verify draft where required. Carbon monoxide alarms belong on every level of the home, full stop.

A few field notes from London homes

A two story in Oakridge had an icy main floor and a sweltering primary bedroom every July. The static pressure was 0.74 inches with a 2 ton air conditioner and a 1 inch MERV 13 filter. We swapped the filter rack to a 4 inch media cabinet, added a 10 by 20 return in the upstairs hallway, and opened a balancing damper to bias 15 percent more air to the second floor in cooling season. Static dropped to 0.46, coil delta T stabilized, and the bedroom sat within 0.5 C of the main floor without a zoning panel.

In an Old South bungalow, a finished basement boxed the trunk tight. Return air relied on a panned joist above a laundry room with visible gaps. We sealed the panned return with duct board, moved the filter into a tight cabinet, and lined the return drop. Noise fell by half, dust complaints faded, and a back bedroom that had seen only a whisper of flow finally met its design CFM.

When to call a pro and what to ask

If you have uneven rooms, noisy registers, frequent furnace limit trips, or an AC that ices, you are looking at airflow until proven otherwise. For furnace repair, ask the technician to measure static pressure and room CFM rather than only swapping parts. For larger upgrades, pick a contractor who talks about ducts alongside equipment. The better shops in heating and cooling london ontario will speak in numbers, not guesses, and will put a manometer on the system before quoting a fix.

Ask to see:

Current total external static pressure and the equipment’s rated maximum Pressure drop across the filter and coil Proposed duct changes and their expected impact on static and CFM

If you hear that none of this is necessary, keep looking. Good airflow is measurable and repeatable.

Keeping it that way

Airflow work is not a one-and-done if filters clog and dampers get bumped during storage season. Mark damper positions with a paint pen and note a summer and winter setting if needed. Check filters on a schedule that matches your home’s reality, not the calendar on the box. After renovations, have a technician check static pressure again. Minor changes, like a new return grille size or an added bath fan that ties into an HRV, can shift the balance.

Homes in London can be stubborn in their comfort quirks. The clay soil moves with freeze and thaw, basements get finished and re-finished, and equipment evolves. Through those changes, the physics of air does not change. Keep resistance low, keep paths open, and match equipment to the duct system. Whether you are investing in a new furnace installation or calling for furnace repair after a frustrating season, give airflow the attention it deserves. Your system will run quieter, your rooms will feel even, and your energy bills will make more sense.

Hometown Heating and Cooling — Business Info (NAP)

Name: Hometown Heating and Cooling

Website: https://www.hometownhc.ca/
Email: [email protected]
Phone: (519) 425-0555

Service Area: London, Woodstock, and Ingersoll (Southwestern Ontario)

Ingersoll Location

Address: 113 Mutual St N, Ingersoll, ON N5C 1Z8
Map/listing URL: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.042608,-80.8860254,17z/data=!3m1!4b1!4m6!3m5!1s0x882e9bfee0d53bf3:0x9f78b1810f24ad23!8m2!3d43.0426041!4d-80.8834505!16s%2Fg%2F1tdgqgkq

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London Location

Address: 45 Pacific Ct Unit #11, London, ON N5V 3N4
Map/listing URL: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.0088901,-81.1800363,17z/data=!4m6!3m5!1s0x882c1f2183b77adf:0x7511cc8383025dcb!8m2!3d43.0101465!4d-81.1752898!16s%2Fg%2F11fsm535_n

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Hours:
Monday-Friday: 8:00AM-5:00PM
Saturday & Sunday: Closed

Open-location code (Plus Code): 2R6F+3V London, Ontario

Socials (canonical https URLs):
Facebook: https://www.facebook.com/Hometownhandc
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https://www.hometownhc.ca/

Hometown Heating and Cooling provides residential HVAC services across London, Woodstock, and Ingersoll in Southwestern Ontario.

Services include heating and cooling installation and repair, fireplace services, duct cleaning, ductless mini-splits, and gas line work (service scope varies by job).

The Ingersoll location is listed at 113 Mutual St N, Ingersoll, ON N5C 1Z8.

The London location is listed at 45 Pacific Ct Unit #11, London, ON N5V 3N4.

To contact Hometown Heating and Cooling, call (519) 425-0555 or email [email protected].

For directions, use the listings: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.042608,-80.8860254,17z/data=!3m1!4b1!4m6!3m5!1s0x882e9bfee0d53bf3:0x9f78b1810f24ad23!8m2!3d43.0426041!4d-80.8834505!16s%2Fg%2F1tdgqgkq and https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.0088901,-81.1800363,17z/data=!4m6!3m5!1s0x882c1f2183b77adf:0x7511cc8383025dcb!8m2!3d43.0101465!4d-81.1752898!16s%2Fg%2F11fsm535_n

Landmarks Near London, Woodstock, and Ingersoll

1) Victoria Park (London)

2) Fanshawe College (London)

3) Pittock Conservation Area (Woodstock)

4) Woodstock Art Gallery

5) Ingersoll Cheese & Agricultural Museum

6) Harris Park (London)