By Daniel Watkins, Noble Chimney Sweepers.
Plenty of Mokena homes built in the seventies, eighties and nineties have a fireplace with metal grilles above and below the opening, and sometimes a small fan switch on the side. Those are heat-circulating fireplaces. They are designed to pull room air in near the floor, warm it in a chamber around the firebox, and push it back out the top. When they work, they throw far more heat into the room than a plain open fireplace. When they are clogged, noisy or disconnected, most owners never realize that part of the fireplace exists at all.
After 14 years of sweeping and inspecting fireplaces in the southwest suburbs, I find neglected circulation chambers on a large share of these units. Here is how they work and how to keep them doing their job.
How a heat-circulating fireplace works
A heat-circulating fireplace has an air jacket wrapped around the firebox, with intake grilles low and outlet grilles high. Room air enters the lower grilles, picks up heat from the hot firebox walls, and exits through the upper grilles without ever touching the smoke.
Some units move that air by natural convection alone. Others add a blower mounted under the firebox or behind the lower grille to push more air through. Many factory-built fireplaces use a similar layout, while some masonry fireplaces have a metal circulating form built into the brickwork.
Why the vents stop moving heat
The most common reason is dust. The lower grilles sit right at floor level, so they collect pet hair, carpet fiber, lint and cobwebs all year long. Once that layer builds up inside the channel, airflow drops and the room gets less heat for the same fire.
Other causes include grilles painted shut during a remodel, furniture or a rug pushed tight against the intake, and blowers with fan blades caked in dust. In some homes, the grilles were covered with decorative panels years ago and simply forgotten.
Signs your circulation vents are struggling
Watch for upper grilles that barely feel warm after the fire is fully going, a burnt dust smell coming out of the top vents, a blower that rattles, hums or squeals, and gray fuzz visible behind the lower grille with a flashlight. Any of these tells you the air path needs attention.
What you can safely do yourself
With the fireplace completely cold and the blower switched off at its power source, you can vacuum the lower intake grilles with a brush attachment and wipe the upper grilles. Removable grilles can be lifted out and cleaned. Our DIY chimney and fireplace maintenance guide covers the other homeowner tasks that fit alongside this one.
What you should not do is reach deep into the air jacket, oil or open a blower motor housing, or run the fan with a grille removed. Blower wiring usually sits close to hot surfaces, and a frayed cord or failing motor needs a trained eye.
Why the circulation chamber matters for safety
The air jacket is supposed to be sealed from the firebox, so smoke never mixes with the air you breathe. On an older unit, a crack in the firebox wall or a burned-through seam can let combustion gases or sparks reach that chamber and blow them straight into the room. That is why we look at the firebox and the circulation chamber together during a chimney and fireplace inspection, and why we work to NFPA 211, the national standard for chimneys, fireplaces and vents.
Warped outlet grilles, discoloration above the top vents, or soot coming out of the grilles are all reasons to stop using the fireplace until it has been checked.
Getting it done in Mokena
A sweep visit is the natural time to clean the circulation channels, since the firebox is already open and the dust is already being contained. We are certified, bonded and insured, owner-operated, and we give the price up front before any work begins. Current rates are on our pricing page, and our Mokena chimney sweep and fireplace service page covers what we handle in town.
Call (708) 432-5747, 7 days a week from 7 AM to 7 PM, and we will get those grilles moving heat again before winter.
Frequently asked questions
How do I know if my fireplace is heat-circulating?
Look for metal grilles or louvers above and below the fireplace opening, and sometimes a fan switch or speed knob on the side or under the firebox. A plain brick opening with no grilles is usually a standard fireplace.
Do heat-circulating vents need to be cleaned every year?
A yearly cleaning is a good habit, especially in homes with pets or carpet. Dust in the lower channel cuts heat output and creates a burnt smell the first time the fireplace runs.
Why does my fireplace blower make a rattling noise?
Rattling or squealing usually means dust buildup on the fan blades, a loose mount, or worn motor bearings. The blower should be checked by a technician rather than taken apart at home.
Can I add a blower to a fireplace that does not have one?
Some factory-built models accept a listed blower kit made for that exact unit. Only a kit approved by the manufacturer for that model should be installed, and many units do not accept one at all.
Is it normal for the grilles to get hot?
The upper grilles are meant to get warm and blow heated air. Grilles too hot to touch briefly, warped metal, or scorch marks above them are not normal and should be inspected.
Can smoke come out of the circulation vents?
It should not. Smoke or soot coming from the grilles suggests a crack or failed seam between the firebox and the air jacket. Stop using the fireplace until it has been inspected.
Should I close off the lower grilles when the fireplace is not in use?
There is usually no need, and blocking them risks forgetting before the next fire. Keeping them clear of rugs and furniture is the better habit.
Does cleaning the vents replace a chimney sweep?
No. The circulation channels carry room air, not smoke. The flue still needs its own sweeping and inspection once a year to deal with creosote and venting problems.
Published October 17, 2026