The Orphaned Water Heater Problem

How a water heater becomes orphaned

For decades, many New Jersey homes vented an atmospheric gas or oil furnace and a gas water heater into the same masonry chimney. The furnace produced most of the hot exhaust and kept the flue warm, which helped the water heater's smaller exhaust rise.

Modern high-efficiency furnaces often vent through plastic pipe out a side wall and stop using the chimney altogether. The water heater keeps its old connection. Now a small appliance is venting alone into a flue sized for much more, sometimes on an exterior wall that stays cold all winter.

Why that can be a problem

Natural draft depends on warm gases rising through the flue. A large, cold flue cools a small exhaust stream quickly. Two problems can follow:

• Poor draft or spillage. Exhaust may rise slowly or, at start-up, spill out of the water heater's draft hood into the room.
• Condensation. Burning gas produces water vapor. When the exhaust cools below its dew point inside the chimney, that water condenses on the flue walls, carrying acidic compounds that attack mortar joints and clay tile.

A New Jersey borough's notice to contractors puts it directly: newer, more efficient equipment produces lower exhaust temperatures, which leads to poor draft and condensation, and an alternate means of venting will probably be needed when appliances are replaced. A furnace manufacturer's installer guide makes a similar point, suggesting that where a chimney is oversized or condensation is a problem, the chimney be used as a chase for a B-vent or flexible liner.

Clues to watch for

• White crust, rust, or water at the base of the chimney or the cleanout door.
• Rust or water stains on the water heater's vent connector or draft hood.
• Crumbling mortar or flakes of tile collecting at the bottom of the flue.
• Staining or efflorescence on the outside of the chimney. See white staining on brick.
• A furnace that was replaced recently with one that vents through the wall.

None of these alone proves the venting is wrong. They are reasons for an inspection. If a carbon monoxide alarm sounds, leave the house and call 911.

What codes and New Jersey towns look at

Building codes and manufacturer instructions generally size gas vents using venting tables, including tables for venting appliances into masonry chimneys. Your town's construction office can confirm what applies. A New Jersey borough's guidance to contractors points to those tables and notes that, for exterior chimneys in this climate, the permitted applications are limited.

New Jersey's standard chimney verification form for replacement of fuel-fired equipment asks whether the chimney is in good repair, clear of obstruction, and appropriately lined and sized for the appliances being installed. It records the liner's manufacturer, listing, material, and dimensions. Towns commonly require this form, completed by a professional, when a furnace, boiler, or water heater is replaced, and some include a final inspection of the venting.

Typical solutions

Which option fits is a question for an inspection and the people doing the appliance work. For liner choices, see stainless, cast-in-place or clay liner?

Plan it with the furnace replacement

The best time to address an orphaned water heater is before the new furnace is installed. If the HVAC contractor knows the water heater will be left alone in the chimney, the venting plan can include it. Ask your installer whether the water heater's venting will be evaluated, who will complete the chimney verification, and what happens if the chimney needs a liner.

If the furnace was replaced years ago, it is still worth having the chimney inspected. Condensation damage happens slowly and out of sight.

How we inspect

We look at the water heater's connector and draft hood, the base of the flue, and the flue itself with a chimney camera when the flue allows. We check the chimney exterior and crown, and note whether the chimney is on an outside wall. You receive the findings with photos before any work is scheduled. CSIA lists the replacement or addition of an appliance as a reason for a Level 2 inspection, which includes a video examination of the flue.

Next step

Replacing a furnace or water heater, or already see signs of condensation? Request an assessment. See our chimney liners and furnace and boiler flue services, and our inspection before a new appliance.

Questions homeowners ask

Sources

1. Borough of East Rutherford, NJ: Chimney Notice
2. NJ DCA Form F370: Chimney Verification for Replacement of Fuel-Fired Equipment
3. Trane gas furnace installer's guide (venting section)
4. Lawrence Township, NJ: Replacing a Furnace
5. CSIA: The Three Levels of Chimney Inspections

This guide is general information. It can't diagnose a specific chimney; an inspection can.