A carbon monoxide alarm sounding is the signal to leave the home at once and call emergency services from outside.
If you smell gas, leave and call the gas utility and emergency services once outside.
Why venting matters for water heaters
A fuel-fired water heater produces combustion gases that must leave the house reliably. How that happens depends on the heater. Atmospheric gas and oil-fired heaters rely on warm gases rising through a flue into a chimney. Power-vented heaters use a fan to push gases out, often through a side wall. Many tankless and condensing units use sealed venting systems specific to the model. Electric and heat pump water heaters need no venting at all.
The venting has to suit the specific appliance. We do not describe venting rules here, and we do not judge anyone's existing arrangement from a web page. What we can say is that whenever a water heater or the appliances sharing its chimney change, venting is one of the first things the installer looks at.
When venting gets reassessed
- Replacing a fuel-fired water heater, even like-for-like
- Changing fuel, such as oil to propane
- Removing or replacing the boiler that shared the chimney with the water heater
- Moving to a power-vented, tankless or sealed-combustion unit
- Moving to electric or heat pump, which leaves an old flue connection to deal with
Old chimneys in Connecticut houses
Colonial-era and 19th-century houses often have large masonry chimneys that were built for fireplaces and stoves, later adapted for coal, then oil boilers and water heaters. Postwar homes frequently have a single chimney shared by an oil boiler and a water heater. When the boiler is replaced with equipment that vents differently, or removed altogether, the water heater may be left venting into the chimney on its own, which can change how that chimney behaves. The installer assesses whether the arrangement still suits the heater, and explains the options if it does not.
Common options
| Situation | Options the installer may discuss |
|---|---|
| Existing chimney suits the new heater | Reuse it with a new flue connection |
| Chimney no longer suits the heater on its own | Chimney work by a qualified chimney professional, or a different venting approach |
| No practical chimney route | A power-vented or sealed-combustion unit vented through a side wall |
| Avoiding venting altogether | An electric or heat pump water heater |
Venting options priced so you can compare.
What to leave alone
- Flue pipes, draft hoods and barometric dampers
- Side-wall vent terminations, including snow and ice around them
- Any chimney cleanout or connection
If you notice soot, a changed smell near the heater, or water around the flue connection, call and describe it.
What we do and do not do
The local installers assess and install venting for the water heaters they fit. Chimney repair and chimney relining are specialist work for a chimney professional, and boilers and heating systems are outside this service. When the assessment shows chimney work is needed, the installer will explain why and what the alternatives are.
Types of venting, briefly
Atmospheric
The oldest and simplest approach. Warm exhaust rises through a draft hood and flue pipe into a chimney. It depends on the chimney drawing properly, which is affected by the chimney's size, condition and what else uses it.
Power-vent
A fan pushes exhaust out, usually through a side wall. It frees the heater from the chimney but adds a fan and an electrical connection, and the termination outside needs to stay clear.
Direct-vent and sealed combustion
The heater draws combustion air from outside and sends exhaust out through dedicated piping, keeping combustion separate from the room. Common on newer and tankless units.
Condensing
Units that extract enough heat from the exhaust to produce condensate, which must drain, and which vent through piping made for that purpose.
Things worth mentioning when you call
- Soot or dark staining around the draft hood or flue connection
- Rust streaks on the flue pipe or the top of the heater
- Water dripping near the flue connection
- A flue pipe that has come loose, sagged or been knocked
- Recent changes to the boiler, furnace or other appliances sharing the chimney
- A side-wall vent that is often buried in snow
These are observations to pass on, not things to fix yourself. The technician will look at them in context.
Shared chimneys in multi-family buildings
In older two- and three-family houses and mill-village buildings, several water heaters and a boiler may all vent into one chimney. When one heater is replaced, the installer considers how the new heater vents alongside the others, not just on its own. See multi-family water heaters.
When switching to electric or heat pump
Moving from a fuel-fired water heater to an electric or heat pump unit removes the need for venting, but it leaves the old flue connection behind. The installer removes the heater's flue pipe and deals with the opening into the chimney. If the chimney still serves a boiler or furnace, how it works for that appliance with the water heater gone is a question for the heating contractor or a chimney professional.
What affects the cost of water heater venting and chimney assessment
- Reusing the existing route against a new vent
- Side-wall venting through different wall constructions
- Whether chimney work is needed from a separate specialist
- The heater type chosen, including electric or heat pump to avoid venting
How long water heater venting and chimney assessment takes in Connecticut
The assessment itself is part of the installer's visit. Reusing a suitable flue adds little time; new side-wall venting adds more. If chimney work is required first, the water heater installation is scheduled around it.
Where the assessment shows the venting needs work before a new heater can go in, the installer will explain the order of jobs, so you know whether the house will be without hot water in between and for roughly how long.
Venting and chimney questions
Why does the venting matter if the old heater worked fine?
A new heater may not vent the same way as the old one, and changes elsewhere, such as a boiler replacement, can alter how a shared chimney behaves. The installer checks it for the specific heater going in.
We are removing our oil boiler. Does that affect the water heater?
It can. If the water heater shared the chimney with the boiler, it may be left venting alone, which can change how the chimney works for it. The installer assesses the arrangement.
Do you reline chimneys?
No. Chimney work is for a chimney professional. The local installers assess venting for the water heater and can suggest alternatives such as side-wall venting.
What is side-wall venting?
A way of venting certain water heaters through an exterior wall, usually with a fan, instead of up a chimney. It suits many houses where a chimney is not practical.
Do electric water heaters need venting?
No. Electric and heat pump water heaters have no combustion, so they need no flue. Heat pump units do need a drain for condensate.
I see soot near my water heater's flue. What should I do?
Call and describe it so a technician can look. Leave the flue and heater controls alone. If a carbon monoxide alarm sounds, leave and call emergency services from outside.
Snow blocks our side-wall vent in winter. Is that a problem?
Mention it to the technician. Blocked vents can cause the heater to shut down. The installer can consider the vent's position when installing or advise on it during service.
Can a tankless unit use the old chimney?
Most tankless units need venting specific to the model, typically not an existing masonry chimney. The installer plans the route.
Can a new water heater share a chimney with our boiler?
Often it can, but it depends on the chimney and both appliances. The installer assesses the shared arrangement whenever either one changes, and explains any changes needed.
Why does the installer ask what else uses the chimney?
Because how a chimney behaves depends on everything venting into it. A boiler, furnace or second water heater sharing the flue affects how well it works for the new heater.