The call comes in every winter. The homeowner turns on the heat or the ventilation kicks in and a blast of cold air comes through every supply register in the house. The furnace is working. The thermostat is set correctly. The filter is clean. Nothing is obviously wrong except the house just got colder when it should have gotten warmer.
This is the cold air dump problem. It is one of the most common fresh air system complaints in Canadian residential construction and the cause is almost always the same wiring error. The fix is one component, installed once, and it works permanently.
What Is Actually Happening
On a fresh air ventilation system, the HAC motorized inline damper on the fresh air duct and the furnace fan are two separate components that both need to operate on a ventilation call. The damper opens to bring outdoor air into the duct run. The furnace fan runs to distribute that air through the house.
The problem happens when both are wired to energize at the same moment. The damper gets a signal and starts to open. The furnace fan gets a signal and immediately starts running. The damper takes several seconds to fully open. During those seconds the furnace fan is pulling air through a partially open damper — outdoor air at whatever temperature it is outside, moving through the duct and out the supply registers before the system has any chance to temper it.
In July that is mildly uncomfortable. In January in Alberta at minus 25, that is a blast of freezing air through every room in the house for 10 to 15 seconds at the start of every ventilation cycle. Homeowners notice it immediately and call the contractor.
Why It Happens
The most common field installation on a fresh air system wires the HAC damper and the furnace fan in parallel. Same signal, same moment, both energize together. That works electrically. The damper opens, the fan runs, the ventilation cycle completes. On paper it looks correct.
The problem is that wiring them in parallel eliminates the sequencing delay the system needs. The damper has to be fully open before the fan starts. On a correctly sequenced system the fan waits for a confirmed open signal from the damper's end switch before it energizes. That 5 to 10 second gap between damper opening and fan starting is what prevents the cold air pulse.
Most fresh air installations in the field do not have this sequencing. The damper and fan are wired in parallel and the homeowner lives with cold air blasts every ventilation cycle or the contractor gets callbacks every winter.
The Fix
The ADP-0241-S5A Interface Relay Adaptor is built specifically to manage this sequencing. It is the correct specification for any fresh air installation to Canadian or US ventilation code and it is the correct retrofit for an existing system producing cold air discharge.
The sequence with the ADP-0241-S5A works like this:
- The ventilation controller calls for fresh air.
- The ADP-0241-S5A energizes the HAC damper and the damper begins to open.
- The end switch on the HAC confirms the blade has physically reached full open.
- The ADP receives that confirmation and only then energizes the furnace fan.
- The fan runs with the fresh air path fully open. No cold pulse.
- When the cycle ends, the sequence reverses — fan off first, then damper closes.
That reversal at the end of the cycle matters too. On a parallel wired system the damper and fan de-energize at the same moment. The fan is still moving air as the damper starts to close, pulling a last bit of outdoor air through a partially closing blade. The ADP-0241-S5A stops the fan first, then closes the damper, which eliminates that tail-end cold blast as well.
What the HAC Damper Needs to Have
The ADP-0241-S5A requires an end switch signal from the damper to complete the sequencing. The end switch is what tells the ADP the blade has physically reached full open. Without it the ADP has no position confirmation and cannot hold the fan off until the damper is ready.
If the existing HAC on the fresh air duct does not have an end switch, the ADP-0241-S5A cannot sequence correctly. Check the damper part number. The end switch is indicated by the S prefix in the configuration code. HAC-0611-SPO has an end switch. HAC-0610-OPO does not.
If the damper does not have an end switch the options are to replace it with the correct variant or add a field-installed end switch where the damper construction allows. On a new installation, order the HAC in the SPO configuration — Power Open action with relay and end switch included.
For help choosing the right HAC configuration, see the fresh air damper action selection guide.
Is This a Code Requirement or Just a Comfort Issue?
Both. The proving sequence — the fresh air damper must confirm open before the distribution fan runs — is part of ventilation code compliance on new construction in Canada and the US. Wiring the damper and fan in parallel does not satisfy that requirement on a permitted installation. The ADP-0241-S5A and its end switch proving logic are what make the installation code compliant, not just more comfortable.
On existing systems where the homeowner is already complaining, the ADP-0241-S5A retrofit solves the comfort problem and brings the sequencing up to current code practice at the same time.
Common Questions
Can I just add a timer relay instead? A fixed timer relay adds a delay but does not prove damper position. On a warm day when the damper opens quickly the timer waits longer than needed. On a cold day when the blade moves slowly or there is ice on the pivot, the timer may release the fan before the damper is actually open. The end switch proves physical position regardless of temperature. The ADP-0241-S5A is more reliable than any timer solution.
Will this work on an HRV or ERV system? Yes. Any application where a HAC damper on a fresh air duct needs to prove open before a fan energizes is a direct application for the ADP-0241-S5A. HRV and ERV systems using the furnace fan for distribution work the same way. Confirm wiring with the colour diagram included in the ADP box.
Does the A/C circuit get affected? No. All ADP models are designed so the relay logic does not affect the air conditioning circuit. The A/C system operates independently on all ADP installations.
The homeowner says it has always been this way. Is this a new problem? It is not new, it just was never fixed. Parallel wired fresh air systems have always produced cold air pulses at the start of ventilation cycles. Homeowners either get used to it or assume it is normal. It is not normal and the ADP-0241-S5A eliminates it.
What to Order
- ADP-0241-S5A for fresh air damper and furnace fan sequencing on a 24 Vac system
- HAC in SPO configuration if the existing damper does not have an end switch
Both are stocked at HVAC wholesalers across British Columbia, Alberta, Saskatchewan, and Manitoba. Call 1-800-661-7382 if you need help confirming the right configuration for a specific installation.
View the HAC Inline Air Control Damper
Hoyme Manufacturing is a CSA-certified manufacturer of motorized dampers and airflow controls based in Camrose, Alberta. Products are available through HVAC wholesalers across Western Canada.