Oil heat chimneys

Oil Furnace & Boiler Chimney Service in CT

Your heating technician takes care of the burner. The chimney that carries its exhaust needs its own attention, and in Connecticut, where oil heat is common, it often gets overlooked.

Call (203) 779-6787 Get a callback

Sunday to Friday

The short answer

An oil furnace or boiler chimney should be inspected every year and cleaned when soot and scale build up, because oil exhaust is acidic and slowly eats away at clay tile and mortar. Debris collecting at the base of the flue can block venting and push carbon monoxide back into the house. A cleaning with a Level 1 inspection runs about $150–$350 as a ballpark.

The A Class Chimney crew with stainless-steel chimney liners next to the work truck — A Class job photo

Why oil heat is hard on a chimney

Oil combustion leaves soot, and the exhaust carries sulfur compounds and water vapor. When that exhaust cools inside the flue, some of the vapor condenses into a weak acid. Year after year, the acid softens mortar joints and the glazed face of clay flue tiles, which begin to flake and break down.

Newer, more efficient oil boilers and furnaces can make this worse in an old chimney. They send cooler exhaust up the flue, so more of it condenses, especially in a large masonry flue originally sized for an older, hotter-running unit, or in a chimney on an outside wall that stays cold all winter.

The flakes of soot and deteriorated tile, usually called scale, drop to the bottom of the flue. Over the years they pile up at the base, below the point where the smoke pipe enters the chimney, and can grow until they partly block the opening the exhaust needs.

In many Connecticut basements the oil boiler and the water heater vent into the same flue. That setup can work when the flue is sized for both and a heating technician has set it up correctly, but it also means a clogged base or a failing liner affects two appliances at once.

Warning signs, and who to call for each

An oil heating system has two halves: the appliance and the chimney. Knowing which half a symptom points to saves you a wasted visit.

What you notice	What it may mean	Who should look at it
Flakes, soot or tile pieces at the chimney cleanout door	Scale building up at the base of the flue	Chimney technician
White staining or crumbling brick near the top of the chimney	Acidic condensation working into the masonry	Chimney technician
A rusted or corroded chimney cap	Acidic exhaust attacking the metal	Chimney technician
Soot around the smoke pipe or barometric damper	The burner or draft may not be set correctly	Heating technician first, then a flue check
Puffback: soot blown into the basement or living areas	A burner misfire, sometimes with a partly blocked flue	Heating technician, plus a chimney inspection before relying on the system
CO alarm sounds	Exhaust may be entering the living space	Leave the house and call 911

Chimney symptom checker

Tick what you have noticed and see what it usually means.

Our part of the job, and your heating tech’s part

A Class works on the chimney side only. We inspect and clean the flue, clear scale from the base, check the cap, crown and masonry, and install stainless-steel liners when the old flue is no longer sound. We do not repair, tune or replace oil burners, furnaces or boilers.

Your licensed heating technician handles the appliance: the burner, the combustion test and the draft settings. If you already book a yearly tune-up for the burner, have the chimney looked at around the same time, so that whatever one side finds, the other can follow up before the heating season is in full swing.

When an oil flue needs relining

A clay-tile flue that has cracked, lost pieces of tile or shed enough scale to clog the base keeps getting worse, and cleaning only buys time. The usual fix is a stainless-steel liner run from the top of the chimney down to the smoke pipe connection and sized to the appliance it serves. It gives the exhaust a smooth, correctly sized, corrosion-resistant path and keeps the acid off the masonry. Our page on chimney liner and flue repair shows how the work is done.

Relining also deserves a conversation whenever the heating system changes. NFPA 211 recommends a Level 2 inspection when you change the appliance or the fuel, because a new boiler, or a switch from oil to gas, may need a different flue size than the one you have now.

Stainless-steel relining: about $1,500–$4,000+ as a ballpark; see the chimney liner cost guide for what moves the price
Level 2 inspection when the appliance or fuel changes: about $250–$500 as a ballpark
Exact prices are set in writing after the $59 on-site inspection

If you are converting away from oil

When you switch from oil to gas, propane or a heat pump, the new system may vent into the old chimney through a new liner, out through a sidewall with its own vent pipe, or not need a flue at all. Your heating contractor decides that based on the appliance and its installation instructions. If the new unit will use the chimney, the flue should be inspected and usually relined before it goes into service.

If nothing will vent into the chimney anymore, don’t leave the old flue open to the weather. Cap it so rain and animals stay out, then decide whether to keep, seal or take down the chimney. Our guide on what to do with an unused chimney lays out the options.

Before each heating season

A short list to work through in September or October, before the boiler is running every day.

Book the burner tune-up with your heating technician
Have the chimney flue inspected, and cleaned if scale has built up at the base
Look at the chimney top from the ground: is the cap there, straight and free of heavy rust?
Check for white stains on the brick or loose bricks near the top, especially on the side facing the weather
Keep the area around the boiler and the chimney cleanout clear of stored boxes
Make sure the cleanout door is closed tight; an open one can upset the draft
Test the CO and smoke alarms, and replace batteries or any alarm past its replacement date

Booking an oil chimney inspection with A Class

The steps are the same whether you have spotted a warning sign or are simply catching up on maintenance.

A quick callCall (203) 779-6787 and tell us the type and rough age of your heating system, if you know it, and whether a water heater shares the chimney.
$59 on-site inspectionWe check the flue with a camera, look at the base through the cleanout, and photograph the chimney top, using a drone when the roof is hard to see.
Photos and findingsYou get photos of the flue walls, the base and the top, with a plain explanation of what we found and anything your heating technician should see.
Written priceCleaning, relining or masonry repair is priced in writing before any work begins.
Clean workDrop cloths go down around the boiler area and the cleanout, and the basement is left the way we found it.

Talk to a chimney pro

Prefer we call you?

Three quick taps and a real person from A Class Chimney calls you back to set up a $59 on-site inspection.

Two A Class techs on top of a brick chimney, photographing what they find — The A Class crew

$59 on-site visit and written estimate
Photos of everything we find
A written price before any work starts
Licensed and insured in Connecticut

Call (203) 779-6787

Sunday to Friday

Get a callback

What do you need?

When?

Where should we call you?

Please enter your first name.

Please enter a 10-digit US number.

Please add your town.

Free, no obligation. Privacy

FAQ

Common questions

NFPA 211 recommends inspecting every chimney once a year and cleaning whenever the inspection shows soot or scale building up. Oil flues often need cleaning less often than wood-burning ones, but scale at the base is common in older clay-lined chimneys. The yearly inspection tells you whether a cleaning is due.

That depends on the company. Many tune-ups focus on the burner and the appliance itself rather than a full inspection of the masonry flue from base to top. Ask your provider exactly what their service covers. Inspecting the flue, clearing the base and checking the cap and crown is chimney work.

A puffback happens when an oil burner misfires and a burst of pressure pushes soot out of the appliance, sometimes through much of the house. The burner itself is a job for your heating technician. A partly blocked flue can be part of the story, so have the chimney inspected before relying on the system again.

No. A wood-burning fireplace and an oil appliance should each have their own flue. Sharing one can upset the draft for both and push exhaust into the house. Many Connecticut chimneys have two or more flues side by side for this reason, and an inspection confirms which appliance uses which flue.

Not in every case. A sound clay-tile flue of the right size for the appliance can be fine. A liner becomes the fix when the tiles are cracked or deteriorating, when the flue is much larger than the appliance needs, or when the appliance manufacturer calls for one. The inspection and the appliance’s specifications decide it.

Get everyone, including pets, out of the house and call 911 from outside. Carbon monoxide is colorless and odorless, and early symptoms can feel like the flu. Don’t go back in until responders say it is safe. Then have the appliance checked by a heating technician and the flue checked for blockage. More in our carbon monoxide guide.

Keep reading

Related guides and services

Chimney Liner & Flue Repair Chimney Liner Cost in Connecticut Chimney Liner Types: Stainless, Clay or Cast-in-Place?Chimneys and Carbon Monoxide: What to Know Chimney Cleaning & Inspection in CT

Have us take a look

$59 on-site visit, photos of what we find and a written price before any work. Licensed and insured in Connecticut.

Call (203) 779-6787 Get a callback Book online