Is an Open Coil Heater the Missing Piece in Your HVAC Upgrade Plan?

Introduction

When a building or plant plans an HVAC upgrade, the talk usually goes to fans, filters, controls and ductwork. Heating gets a single line on the spec sheet, often just “replace like for like.” That’s understandable, because heat only gets noticed when it fails. But the heating stage decides how quickly a space recovers on a cold morning and how hard your fans have to push. An Open Coil Heater deserves a place in that early discussion, and at Heaters And Sensors Inc. we’d rather you ask the question now than find out after the ductwork is closed up.

What an Open Coil Heater Actually Is

Picture a metal frame that slides into a duct. Across the frame, resistance wire (usually a nickel-chromium alloy) is wound into coils and held in place by ceramic insulators. Current runs through the wire, the wire heats up, and the air moving past carries that heat downstream. Nothing sits between the element and the airflow.

It sounds almost too simple, which is probably why this design is still found in ventilation ducts, drying lines and make-up air units long after newer options arrived.

Why Facility Teams Keep Coming Back to It

Ask the people who maintain these systems and a few reasons come up again and again:

• The heat goes straight into the air, so temperature responds quickly when the controls call for a change.

• Air passes through with very little restriction, which keeps fan energy in check.

• Everything is out in the open, so a technician can spot a broken coil or a cracked insulator at a glance.

None of that makes it the right answer everywhere. It simply explains why the design has lasted.

Where It Belongs, and Where It Doesn’t

Bare wire likes clean, steadily moving air. Ducts that need tempering or reheat, make-up air units pulling in cold outdoor air, and industrial drying or curing lines are all good matches. Dusty shops, damp spaces, corrosive vapours and hazardous areas are not. In those conditions a sheathed element is usually the safer choice, and we’ll tell you so when you ask. Better to hear it before purchase than after.

Retrofits are worth a look too. The frames are compact, and many can be fitted into an existing duct section without a major rebuild, provided the electrical supply can handle the load.

Get the Size Right First

Sizing is where plans most often go sideways. A common starting formula is kW = CFM × temperature rise in °F ÷ 3,160. Say you move 2,000 CFM and want to lift the air by 30°F. That works out to roughly 19 kW.

Treat that number as a starting point only. Voltage, phase, available amperage and a modest safety margin all shift the final answer. Staging helps as well: splitting the load into two or three steps lets the unit run partially on milder days instead of cycling hard on and off. When we help a customer choose an Open Coil Heater, we begin with airflow and target temperature, never with a catalogue number.

Safety Controls Are Not Optional

Since the wire is exposed, protection does real work here. A proper installation includes an airflow proving switch so the coils can’t energise without air moving, high-limit cutouts (one automatic reset, one manual), and suitable contactors or solid-state relays for staging. At Heaters And Sensors Inc. , we wouldn’t quote a bare-element heater without going through these items first.

Questions Worth Asking Before You Order

Put a few plain questions to whoever is supplying the heater. What’s the real airflow range through the duct, including the lowest speed the fans will run at? Will a single stage do, or does the building need smoother control? What voltage and phase are available at the panel, and how much spare capacity is there? Is there enough straight duct run for air to move evenly across the coils? Written answers to these four questions save more back-and-forth than any datasheet.

Keeping It Healthy After Installation

Maintenance is light but shouldn’t be skipped. Before heating season, check the coils for sagging or heavy dust, look over the insulators for cracks, tighten terminals, and test the limit controls and the airflow switch. Jot down what you find each time. Ten minutes of looking beats an emergency call in January.

If the heater sits idle all summer, give it a visual check before the first cold week too. Dust settles on coils over the months, and it can give off a burnt smell the first time they warm up. Cleaning it off beforehand spares everyone a false alarm.

About Heaters And Sensors Inc.

Heaters And Sensors Inc. supplies industrial heating and temperature sensing products to Canadian industry, including band heaters, cartridge heaters and thermocouple accessories. We work with engineers, contractors and facility managers who want components matched to the job rather than guessed at. If an Open Coil Heater is on your shortlist, our team can go through your airflow, voltage and space limits with you. 

So, Is It the Missing Piece?

For the right application, quite possibly. A well-planned HVAC upgrade looks at every stage of the air path, and the heating stage shouldn’t be the one copied over from old drawings. Quick response, low airflow resistance and easy servicing make the Open Coil Heater a strong candidate when the air is clean and the controls are done properly. Start with your airflow numbers, settle the safety details early, and plan simple seasonal checks. If you’d like a second opinion, Heaters And Sensors Inc. is happy to help.