Why the Original Ductwork in Your Home Can Sabotage Your Winter Comfort

What you don’t see can truly affect your heating: the downside of old ducts

At AirGreen, we know that many homes in Montreal, Laval, Longueuil, the North Shore, and the South Shore were built many decades ago. In many cases, the original ductwork is still being used — without anyone ever checking if it's suitable for the modern needs of a central heat pump system. The result? Even with a high-performance unit, you might still feel cold in certain rooms, see your bills rise, or hear your unit working harder than it should.

Old ducts: a hidden but common problem

As part of our HVAC installations, we regularly inspect ducts that are:

• Too narrow for the required airflow

• Poorly insulated, especially in attics or crawl spaces

• Bent, crushed, or punctured

• Designed with imbalanced airflow between supply and return

These flaws create static pressure loss, leading to:

• Uneven thermal comfort throughout the house

• Premature wear on the heat pump

• Excessive energy consumption, sometimes as much as 20 to 30%

Real example: Lennox EL18XPV heat pump in Montreal (Ahuntsic)

In January 2025, we were called to a century-old home in Ahuntsic, where a 3-ton Lennox EL18XPV central heat pump recently installed by a competitor was struggling to heat the upper floor.

Our diagnostic revealed:

• Sheet metal ducts from the 1950s, poorly sealed, with significant losses

• No return air in two rooms

• A plenum that was too small for the new variable-speed unit

We then:

• Replaced the main ducts

• Added two strategically placed return ducts

• Recalibrated the system with a balanced airflow output at 450 CFM per ton

Result: Comfort restored, energy bills reduced by 27%, and a very satisfied client.

The importance of proper airflow

A central heat pump requires a constant, well-distributed airflow to operate efficiently. Too often, the original ducts were designed for:

• Gas or oil furnaces, with short and powerful cycles

• Another era, without zoning or balanced ventilation

Modern Inverter heat pumps, such as Fujitsu Airstage, Bosch BOVA, or Lennox EL models, operate differently:

• They continuously adjust their speed

• They require a soft, stable airflow, without losses

Without properly adapted ducts, their efficiency is compromised, even if the unit is high-performance.

South Shore anecdote: excessive noise in the ducts

In Boucherville, a client with a 5-ton Bosch BOVA central heat pump complained about a dull noise in the ducts as soon as the system started up.

After inspection:

• The ducts were too small for the 2000 CFM airflow

• Compressed air was creating whistles and vibrations

• The single return duct was poorly positioned

We then:

• Resized two main ducts

• Added a second return

• Insulated the noisy ducts

Result: Silence restored, comfort improved, and the unit now runs at a reduced speed, making it more energy-efficient.

How to tell if your ducts are to blame?

Here are some warning signs:

• Cold or hot spots in certain rooms

• Noises in the ducts when the system starts up

• Significant temperature differences between floors

• The system runs too long without stopping

• Excessive dust or unpleasant smells

An HVAC audit from our experts allows us to:

• Measure the real static pressure

• Check for thermal losses

• Provide concrete solutions (insulation, balancing, replacement)

Replacing ducts isn’t a luxury, it’s a long-term investment

At AirGreen, we often see clients invest $10,000 in a high-end central heat pump, only to not fully benefit from their equipment due to inadequate ductwork.

That’s why we always recommend:

• A complete duct analysis BEFORE installation

• Structural adjustments when needed

• Using insulation materials with R8 or higher

• Modern variable airflow diffusers

What you gain from this upgrade

• Better comfort in every room

• Reduced energy consumption

• Prolonged lifespan of your heat pump

• A quiet, balanced system

• Better eligibility for LogisVert grants

AirGreen: installations that consider the whole system

We don’t just install a machine. We analyze your entire HVAC system to make sure it’s coherent, durable, and high-performing. Whether it’s a duplex in Laval, a bungalow in Longueuil, or a condo on the North Shore, our certified technicians take into account:

• The year of construction

• The insulation

• The duct configuration

• Any problematic zones

And we always provide a clear report, with recommendations tailored to your reality.