By Johnathan Mason, Ace Chimney Service.
Yes — in almost every McHenry home we reline, the stainless liner should be insulated. A bare liner dropped down a cold exterior chimney runs cool, drafts poorly, and builds creosote faster than the same liner wrapped in a half-inch insulation blanket. The insulation is not an upsell line item you can safely trim; it is what makes the liner behave the way the manufacturer tested it. Here is what that actually means for a house on this side of McHenry County.
Why a cold liner drafts badly
A chimney works because the column of gas inside it is hotter, and therefore lighter, than the outside air. Anything that cools that column weakens the draft.
An uninsulated stainless pipe sitting inside an old masonry shaft is surrounded by cold brick and a dead air gap that the wind moves through. On a 10-degree January morning, the flue gases give up their heat to that brick before they reach the top. The result is a sluggish start, smoke rolling into the room on lighting, and a stove or fireplace that never quite settles into a clean burn.
Insulation is also creosote control
Creosote condenses out of wood smoke when the flue surface drops below roughly the dew point of the exhaust. Keep the liner warm and most of that material leaves the house as vapor. Let it run cold and it plates onto the steel as sticky, then glazed, deposits.
This is the part homeowners underestimate. Two identical stoves, two identical loads of oak, one insulated liner and one bare — and the bare one comes back to us with noticeably heavier buildup at the annual sweep. Insulation buys you a cleaner flue and a safer one. Our chimney relining service quotes the blanket as standard for exactly this reason.
Exterior chimneys need it most
An interior chimney that runs up through heated living space stays reasonably warm on its own. An exterior chimney — the kind bolted to the outside wall of a 1970s ranch or a split-level, common all over McHenry — is exposed on three sides to whatever the wind is doing.
If your chimney is on an outside wall, treat insulation as mandatory. If it runs up the middle of the house, it is still recommended and still improves performance, but the penalty for skipping it is smaller.
Insulation, clearance, and old chimneys
There is a second reason beyond performance. Many older masonry chimneys were built with framing closer to the brick than current standards allow, and some have cracked or missing tiles that let heat reach that framing. A wrapped, listed liner assembly is how a relining brings a marginal chimney back to a safe condition without tearing out the structure.
An inspection is what tells us which situation you have. We look at tile condition, the smoke chamber, the crown, and how the chimney is framed at each floor before recommending a liner size or insulation method. Book a chimney inspection first; the liner spec follows from what we find.
Blanket, pour, or nothing
There are two practical ways to insulate. A ceramic blanket is wrapped around the liner and secured with mesh and bands before the liner goes down — it is the common choice, it is repeatable, and it fits most flues. A pour-in vermiculite mix is used when the shape of the shaft makes wrapping impractical, filling the space around the liner from the top.
The blanket needs about an inch of total diameter to pass, so the existing flue has to be measured honestly. If the shaft is genuinely too tight, the answer is a smaller liner or a pour, not a bare pipe and crossed fingers.
Talk to us before you compare quotes
If you are collecting relining quotes in McHenry, ask each company in writing whether the liner is insulated and how. It is the single biggest reason two quotes for “the same job” differ. We have been doing this for 29 years, we are insured and bonded, and we price every job up front — see the pricing page or call (815) 320-0883, seven days a week, 7 AM to 7 PM.
Frequently asked questions
Does an insulated liner really improve draft that much?
On an exterior chimney, noticeably. Owners most often report that the fire lights without a smoke rollback and that the stove holds a steadier burn overnight.
Can insulation be added to a liner already installed?
Only by pulling the liner and rewrapping it, or by pouring insulation around it from the top if the gap allows. Neither is a small job, which is why it is worth specifying at installation.
How thick is the insulation blanket?
Half an inch is the common thickness for residential liners. That adds roughly an inch to the outside diameter once it is wrapped and banded.
What if my flue is too narrow for a wrapped liner?
We either step down to a smaller liner that still suits the appliance, or use a pour-in insulation around a bare liner. Tile can sometimes be removed to gain room, but that is a bigger project.
Does insulation help a gas appliance too?
It helps, mainly by keeping the flue warm enough to limit condensation. Gas exhaust is wet, and a cold liner lets acidic moisture collect and corrode the steel.
Will an insulated liner still need annual sweeping?
Yes. It builds less deposit, not none. Annual service also checks the top plate, cap, and the seal where the liner meets the appliance.
Is a cap needed on a relined chimney?
Always. The top plate seals the shaft and the cap keeps rain and animals out of the liner. Our caps and crowns page explains what goes on top.
How long does a relining job take?
Most single-flue jobs are one day once we have measured and ordered the correct liner. Complicated offsets or a second flue can extend that.
Published October 11, 2026