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Frequently Asked Questions
Why is the airflow interlock so critical?
Still air carries no heat away from the elements.
Temperature rises until something fails.
That failure sits next to building fabric.
Proof of airflow must precede energising.
A manual-reset thermal cutout backs it up.
Neither is an optional accessory.
What is wrong with proving the fan is running?
It does not prove air is moving.
A closed damper satisfies that signal.
So does a completely blocked filter.
The heater then energises into still air.
Airflow switches sense the air itself.
Differential pressure sensing is better still.
How does watt density relate to airflow?
Heat into a duct area at a given airflow.
Less air means hotter element surfaces.
A heater specified without stating airflow may run hot.
Minimum airflow becomes a hard limit.
It belongs on the drawing and the label.
Variable volume systems need particular care.
Open coil or finned tubular?
Heat transfer against robustness.
Open coil transfers best and costs least.
It suits clean, dry air only.
Finned tubular tolerates dirt and moisture.
It is the choice where condensation is possible.
Match the element to the airstream.
What clearances apply?
Those the manufacturer specifies, upstream and down.
Combustible material must be kept clear.
Flexible duct close downstream is a common breach.
Bends too near the heater cause hot spots.
Straight duct is required either side.
These are routinely ignored on site.
Can it be controlled in stages?
Yes, and it usually should be.
Staging matches output to demand.
It reduces cycling and temperature swing.
Solid state control gives finer modulation.
That suits close temperature holding.
Simple on-off suits frost protection.
What is checked at commissioning?
The interlock, by actually blocking airflow.
Confirm the heater de-energises.
Test the thermal cutout and its reset.
Verify minimum airflow at the design condition.
Check clearances physically, not on drawings.
Record the results.