When it comes to water heater expansion tanks, one size definitely does not fit all.
Instead, the expansion tank size you need depends on your water heater capacity, your home’s water pressure level, and your plumbing system’s temperature rise. Most 40- to 50-gallon water heaters require a 2-gallon expansion tank, but pressure levels can change that.
Why is this decision important? An undersized expansion tank can’t handle the volume of heated water that it should. And an oversized model might not operate as efficiently as a properly-sized one.
In this guide, we’ll look closely at this issue of expansion tank sizing. We’ll also discuss how you can figure out the right tank size for all your water heating needs.
Quick Takeaways
- Above all, expansion tank size depends on two factors: water heater size and water pressure.
- If you have a 40– or 50-gallon heater, you’ll probably need a 2-gallon expansion tank.
- If you have a higher-than-average level of incoming pressure, you’ll need a larger-than-average tank.
- Undersized tanks cannot relieve pressure properly, and they’ll fail early on.
- A professional should verify your pressure before an expansion tank installation.
Why Expansion Tank Size Matters
As we once learned in science class, water expands as it’s heated. Therefore, if your water heater’s expansion tank is too small, it won’t have enough room to absorb that higher volume of water.
As a result, the pressure inside your water heater’s closed system will build up — perhaps to dangerous levels.
Additionally, all that extra pressure will activate your water heater’s pressure relief valve more often than it should be activated. Then your water heater could wear out prematurely.
Generally speaking, oversized water heater expansion tanks aren’t dangerous, and they usually work decently. Even so, larger expansion tanks usually cost more, and they take up more room. Why waste money and interior space?
On top of that, when an expansion tank is too large, it might not function at peak levels. Thus, your water pressure could fluctuate sometimes.
Plus, oversized expansion tanks often have standing water inside them. And that water can stagnate and lead to microbial and fungal growth.
In short, incorrect tank sizing can:
- Shorten water heater lifespans
- Cause unnecessary temperature and pressure (T&P) valve discharges
- Lead to leaking or premature tank failure
What Determines the Size of an Expansion Tank?
When it’s time to buy a new expansion tank, keep these factors in mind:
Water Heater Tank Capacity
First of all, what’s your water heater’s maximum capacity: 30 gallons, 50 gallons, 80 gallons, or some other quantity?
Incoming Water Pressure
Most homes have water pressure levels between 40 and 80 pounds per square inch (PSI). If your home has a PSI measurement above the 60-80 range, take special care when sizing your expansion tank.
Temperature Rise
What is temperature rise? It’s the difference in temperature between the cold water entering your water heater and the heated water.
Be aware: The higher your heater’s temperature settings, the greater your heated water’s volume will be.
General Expansion Tank Sizing Guidelines
For reference, here’s a list of water heater capacities along with the expansion tank sizes they typically require:
- 30- to 40-gallon heater: 2-gallon tank
- 50-gallon heater: 2-gallon tank (sometimes larger due to water pressure)
- 75– to 80-gallon heater: often a 4.5-gallon tank
These are merely rules of thumb, though. Your ideal tank size could vary. For example, high-pressure systems frequently need larger-than-normal tanks.
With all of this in mind, homeowners should always rely on pressure measurements and manufacturer charts when sizing their water tanks.
How to Calculate the Correct Size
To arrive at the best size for your expansion tank, you’d complete these steps:
- Confirm your water heater’s capacity.
- Measure the incoming water pressure.
- Check your manufacturer’s sizing chart.
- Match your PSI and the heater gallons to the expansion tank rating.
However, most homeowners lack the tools and training to calculate these measurements accurately. That’s why it’s crucial to hire an expert.
Signs Your Expansion Tank May Be the Wrong Size
The water heater issues listed below are not normal. In fact, you should call a pro as soon as you notice any of these problems.
They can all indicate an improperly-sized expansion tank:
- A leaking T&P valve
- Popping sounds
- Recurring tank failures
- Fluctuating water pressure
- Premature water heater breakdown
Can I Oversize an Expansion Tank?
It’s safer to oversize your expansion tank than to undersize it. Slightly oversized models are generally safe.
Severe oversizing, however, can negatively affect your water heater’s pressure balance.
When to Have a Plumber Size Your Expansion Tank
So often, DIY plumbing projects lead to faulty installations, injuries, broken fixtures, leaks, water damage, and other problems.
Indeed, these are just some of the tasks that a pro should handle:
- Installing a new water heater
- Replacing an old expansion tank
- Installing a pressure-reducing valve
- Alleviating water heater warranty concerns
- Addressing high PSI readings
Bradenton Benjamin Franklin: The Right Folks for the Right Expansion Tanks
Professional expansion tank sizing provides protection and plumbing problem prevention.
After all, water pressure stress shortens tank lifespans. And improper tank squeezing is often a hidden cause of water heater failure.
For exceptional tank sizing and installation services, Benjamin Franklin Plumbing of Bradenton is always ready to help.
Serving Bradenton, FL, and nearby areas, our punctual plumbers will make sure your expansion tank is the perfect size. And we’ll keep your water heater running as smoothly as possible. So please give us a call at your earliest convenience.
Yes, we size, install, and repair water heaters the right way so pressure problems don’t shorten your system’s life.