If One of Two Water Heaters Fails, Should You Replace Both?
- Hot Water Solutions
- 7 days ago
- 5 min read
Some larger homes use two tank-style water heaters to meet their hot-water demand. The two units may be piped together, installed in series, or assigned to different parts of the house. When one fails, homeowners naturally ask whether they should replace only the problem unit or replace both water heaters at the same time.
There isn’t one answer that fits every home. We look at the age and condition of both units, how they’re connected, and whether the second water heater is likely to develop the same problem soon.
How Old Is the Second Water Heater?
Age is usually the first thing we consider. If both water heaters were installed at the same time, they have experienced roughly the same years of operation and similar water conditions. Even if only one is leaking today, the second may not be far behind it.
Tank-style water heaters generally last around 10 to 12 years, although some fail sooner and others continue working longer. If two units are only five years old and one develops a repairable problem, replacing both would rarely make sense. If they’re both 15 or 20 years old and one tank starts leaking, replacing only one could mean scheduling another replacement in the near future.
Age alone doesn’t make the decision, but it gives us important context.
Is the Second Water Heater Showing Warning Signs?
A water heater doesn’t have to be actively leaking to show signs of deterioration. We inspect the second unit for:
Rust or corrosion
Moisture around the tank or connections
Discoloration near the base
Signs of previous leaking
Inconsistent heating
Unusual burner operation
Worn or outdated components
Installation problems
An unreadable or deteriorated data plate
If the second water heater is the same age and already showing warning signs, replacing both may save the homeowner from another failure, service appointment, and installation cost later. If the second unit is in good condition and considerably newer, there may be no reason to replace it.
Were Both Water Heaters Installed Together?
Two matching water heaters sitting side by side were usually installed as one system. That means they may share:
The same installation date
An expansion tank
Water and gas piping
Shutoff valves
Venting components
A common drain arrangement
Similar usage and operating conditions
Replacing both units at once allows the plumber to evaluate the complete system and make sure the water heaters are balanced and connected correctly. It also avoids creating a mismatched system with one new water heater and one much older unit, although having different-aged water heaters isn’t automatically a problem if the system is properly configured.
How Are the Water Heaters Connected?
The way two water heaters are piped affects what happens when one is removed or replaced.
Water Heaters Installed in Series
In a series configuration, water flows through one tank and then the other. The first unit may preheat the incoming water while the second brings it to the final temperature. Because the units have different roles, they may not experience exactly the same workload.
Water Heaters Installed in Parallel
In a parallel configuration, both tanks are intended to share the hot-water demand. Proper piping is important so one unit doesn’t do most of the work while the other contributes very little. Replacing one tank with a different size or model may require evaluating the piping and flow between the units.
Water Heaters Serving Separate Areas
Some homes have two completely separate water heaters. One may serve the primary bathroom while another serves the kitchen, laundry room, or remaining bathrooms. If they operate independently, replacing one may have little effect on the other. Before making a recommendation, we determine how the system actually works.
Would Replacing One Reduce Your Hot-Water Capacity?
If two water heaters work together and one is taken out of service, the home may still have hot water but much less of it. One remaining 50-gallon water heater may not be enough for a home that previously relied on two 50-gallon tanks. Before temporarily or permanently removing one, consider:
The number of people in the house
Large soaking tubs
Multiple showers used close together
Laundry and dishwasher use
How often fixtures run simultaneously
Whether both heaters serve the whole house
If the household genuinely needs the capacity of two tanks, simply removing the failed unit may create a new problem.
Could You Replace the Two Tanks With a Different System?
When both water heaters are ready for replacement, it may be a good time to consider whether the same setup still makes sense. Depending on the home, available utilities, gas supply, venting, and hot-water demand, the options may include:
Two new tank-style water heaters
One properly sized larger-capacity water heater
A properly sized tankless water heater
Multiple tankless units for very high demand
A different arrangement serving separate areas
That doesn’t mean tankless is automatically the better choice. The existing gas line, venting, electrical supply, installation cost, and household expectations all need to be considered.
Sometimes replacing two tanks with two new tanks remains the most practical option.
A Recent Two-Water-Heater Replacement in Alpharetta
We recently replaced two approximately 25-year-old A.O. Smith 50-gallon gas water heaters in an Alpharetta home. Because both units were the same age and part of the same system, replacing both made more sense than installing one new unit beside a 25-year-old tank. The project included:
Removal and disposal of both old water heaters
Two new A.O. Smith 50-gallon gas water heaters
New drain pans
A new 4.5-gallon thermal expansion tank
Five new isolation ball valves
New gas connectors
New fittings and piping needed to connect to the existing system
That doesn’t mean everyone with two water heaters needs to replace both. In this situation, however, the age of the units and their shared installation made the decision fairly straightforward.
Should You Replace One or Both?
Replacing both water heaters may make sense when:
They were installed together
Both are near or beyond their expected lifespan
The second unit is showing signs of deterioration
Both are needed to meet the home’s demand
Much of the shared piping or installation needs updating
You want to avoid another likely replacement soon
Replacing only one may make more sense when:
The second water heater is considerably newer
The failed component can reasonably be repaired
The units serve different areas independently
The second tank is in good condition
Replacing both provides little practical benefit
At Hot Water Solutions, we’ll inspect the system and explain the options rather than automatically recommending two replacements. Call 678-540-6164 if one of your water heaters has failed or you’re unsure whether both should be replaced.
Because a cold shower should be by choice.
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FAQ Questions for Rich Results
Should I replace both water heaters if only one is leaking?
Not always. If both were installed together and are near the end of their expected lifespan, replacing both may make sense. If the second unit is newer and in good condition, it may not need replacement.
Can I run my house on one water heater instead of two?
Possibly, but the remaining unit may not provide enough hot water for the household. The answer depends on the tank size, number of occupants, fixtures, and how much hot water the home uses.
Can two water heaters be different ages?
Yes. Two different-aged water heaters can operate together if they are properly sized and connected. However, the older unit may require replacement sooner.
Can two tank water heaters be replaced with one tankless water heater?
Sometimes. The tankless unit, gas supply, venting, electrical connection, and plumbing must all be properly sized for the home’s peak hot-water demand.
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