Start with the danger
If a carbon monoxide alarm sounds
Carbon monoxide has no color or smell. Treat every alarm as real.
- Get everyone, pets included, outside into fresh air.
- Call the gas utility or 911 from outside.
- Do not go back in until responders say it is clear.
- Have the heater and vent checked by a licensed plumber before using it again.
Alarms belong on every level and outside bedrooms. Replace them on the schedule printed on the unit.
The four vent setups
| Type | How it works | Typical pipe | Where it exits |
|---|---|---|---|
| Natural draft | Hot exhaust rises on its own | Metal double-wall pipe | Chimney or roof |
| Power vent | A blower pushes exhaust out | Plastic such as PVC or CPVC, per the maker | Side wall or roof |
| Direct vent | Sealed, draws air from outside too | Two pipes or a concentric pipe | Side wall |
| Condensing | Extracts extra heat so exhaust is cool and wet | Plastic or polypropylene, per the maker | Side wall or roof |
| Tankless gas | Sealed combustion, high output | Stainless or plastic, per the maker | Side wall or roof |
The manual names the exact pipe material allowed for your model. Mixing materials or using whatever was left from the last job is a common source of failures.
According to 248 CMR 10.14, no check valve may be placed in the cold supply to a water heater, a standard worth remembering while the heater is being reconnected.
Slope and rise
On a natural draft heater, hot exhaust moves only because it is lighter than the air around it. The vent therefore needs to climb, with horizontal runs kept short and every section pitched upward toward the chimney or roof. A section that sags or runs level lets exhaust cool, stall and spill back into the room.
Power vent and condensing models are the opposite in one way: horizontal runs on those usually slope down toward the heater or the outdoor terminal so condensation drains instead of pooling. Which direction applies depends on the model, and the installation manual decides.
Clearances in plain terms
Hot metal vent pipe cannot touch wood. Maker instructions list how far a vent must stay from framing, insulation and stored items, and a double-wall pipe needs less distance than a single-wall one. Where the pipe passes through a wall, floor or ceiling, a listed thimble or firestop keeps the heat away from the structure.
The heater also needs air to burn. A tank crammed into a closet with no combustion air can run starved, throw soot and produce carbon monoxide. Room volume or openings to the outdoors are part of the design.
Signs the vent is failing
Soot or scorch marks
Black staining around the draft hood or on the top of the tank means flue gas is spilling out into the room.
Rust streaks and white crust
Rust on the vent pipe or white mineral crust at the joints means condensation is running down a flue that is too cool or sloped wrong.
A flame that leans or flickers
A burner flame pulled sideways or lifting off the burner is a sign of poor draft or contaminated air.
Stuffy air or a flue gas smell
A heater room that smells sharp or feels stuffy while the burner runs needs attention at once, even if the alarm is quiet.
Older Danvers houses and gas venting
Danvers has a lot of older housing: Census figures put about 2,930 units at 1939 or earlier, and close to seven in ten homes predate 1980. Many of those houses were built with masonry chimneys, and a chimney that once served an oil boiler is often too large and too cold for a modern, more efficient water heater, so it may need a liner.
Gas service in town is through National Grid. If you smell gas, leave the house and call the gas utility from outside. Local permits run through the inspectional services office on Sylvan Street, and the state rule applies to vent and gas work the same way it does to the tank.
Source type: Census ACS 2020 to 2024 and Town of Danvers utility information
What a vent installation visit covers
A licensed plumber checks the existing chimney or pipe, sizes the new vent to the heater, sets the pitch, seals or supports each joint and tests draft with the burner running. The job ends with a combustion check and a look for spillage at the draft hood. If you are weighing options, water heater replacement gives the broader picture of swapping the tank along with the vent.
Why local permits and salt air matter
Peabody's inspectors issue plumbing and gas permits to licensed plumbers and gasfitters, and its fee schedule doubles the fee when work starts without a permit, so the right sequence matters for Peabody owners. Along the coast, Beverly's flood-prone streets and sea walls point to salt-air corrosion on exposed metal, which includes outdoor vent terminals, so Beverly owners should inspect exterior pipe more often.
Safety checklist: keep it safe between visits
- Keep the area around the heater free of paint, gasoline, aerosol cans and cleaners.
- Never block the draft hood or combustion air openings.
- Test CO alarms monthly and replace them on schedule.
- Have the vent inspected whenever the heater, furnace or chimney changes.
Vent pipe questions
Only if the maker lists plastic for that model, and usually only for power vent or condensing units. Natural draft heaters need metal vent pipe.
Moisture in exhaust condenses on cool pipe and leaves rust or crust. It means the vent is oversized, uninsulated or pitched wrong.
Often it does. A chimney or pipe sized for the old unit may not suit a higher-efficiency one, and the vent should be checked at every swap.
The maker lists the distance for your pipe type, and it differs between single-wall and double-wall. Follow the manual, and let a plumber confirm.
Yes. If you smell gas or a CO alarm sounds, leave first, then call our 24/7 line at (855) 575-2890.
National Grid supplies gas in Danvers, while the municipal Danvers Electric division supplies electricity.