By Johnathan Mason, Ace Chimney Service.
An open masonry fireplace is a wonderful thing to sit in front of and a poor way to heat a house. An insert is the opposite trade: less of the open fire, considerably more heat in the room. Homeowners in Fox River Grove ask us about this every fall, and the part that usually goes unmentioned in showroom conversations is what an insert does to the chimney above it. That is the part worth understanding before you buy.
Why an open fireplace loses heat
An open fire draws combustion air from the room. That air was heated by your furnace, and once it goes up the flue it is replaced by cold air pulled in through every gap in the building envelope. Most of the fire’s radiant heat goes up as well. You feel warm in front of it, and the rest of the house can be measurably cooler while it burns.
What an insert changes
An insert is a closed firebox with a glass door that sits inside the existing fireplace opening. The fire burns in a controlled, sealed chamber, and the heat transfers to the room through the steel or cast body and often a blower, rather than escaping up the flue. The practical differences: far better heat output for the wood you burn, controllable burn rate, no room air disappearing up the chimney, and no open flame to manage.
The chimney requirement people miss
An insert produces a much smaller volume of exhaust than an open fire, and that exhaust is cooler. Vent it into the original oversized masonry flue and the gases slow and cool on the way up, which is the exact recipe for heavy creosote deposits and weak draft. This is why an insert normally requires a correctly sized liner running the full height of the chimney, connected directly to the appliance. That is not an upsell — it is how the appliance is listed and how it is meant to perform. Our chimney relining page covers what that involves.
What has to be checked before installing
- Condition of the existing chimney — a liner should not be run inside a structure that is failing.
- Flue height and dimensions, to size the liner correctly.
- Firebox opening dimensions and hearth extension.
- Whether the crown, cap, and flashing are sound, since a new liner deserves a dry chimney above it.
A chimney inspection before you order anything settles all four, and it is far cheaper than discovering a cracked flue after the appliance is in the room.
Keeping either one working
Both need annual sweeping. An insert is not lower-maintenance — it burns cooler and longer, which builds creosote readily if the wood is damp or the air is choked down too far, and the liner has to be cleaned from the appliance up. Season your wood properly whichever you have. Everything we do is on the chimney services hub, with chimney sweeping details there and rates published on the pricing page.
Booking in Fox River Grove
Ace Chimney Service has served Fox River Grove and McHenry County for 29 years. Insured and bonded, price up front, seven days a week from 7 AM to 7 PM. Call (815) 320-0883.
Frequently asked questions
Does an insert need its own liner?
In nearly every case, yes. The appliance’s smaller, cooler exhaust needs a correctly sized liner to draft properly and to avoid rapid creosote buildup.
Can I put an insert into any fireplace?
Only into one in sound condition with suitable opening dimensions and an adequate flue. That is what a pre-purchase inspection establishes.
Is an insert really warmer than an open fire?
Substantially, because it stops sending room air up the chimney and transfers heat into the room instead of radiating most of it away.
Do inserts still need annual sweeping?
Yes. Long, cool burns produce creosote readily, and the liner must be cleaned as part of the service.
Will an insert work during a power outage?
The fire burns without power. The blower does not, so heat output drops to what the body radiates on its own.
What about a gas insert instead?
A reasonable option with its own venting requirements and annual service needs. Our gas fireplace service page covers what that involves.
Can the original damper stay in place?
The liner passes through the damper area, and the plate is usually removed or fixed open as part of the installation.
Should I inspect before or after buying?
Before. The chimney’s condition determines what will actually fit and vent safely, and that should shape the purchase.
Published August 29, 2026