July 8, 2026

Tank to Tankless: An Essential Guide

What Every Des Moines Homeowner Should Know Before Switching from Tank to Tankless

Switching from tank to tankless is one of the most impactful upgrades you can make to your home’s plumbing system — but it’s not as simple as swapping one appliance for another. It touches your gas lines, venting, electrical system, and plumbing all at once.

Here’s a quick overview of what to expect before you make the move:

Key things to know when switching from a tank to a tankless water heater:

It’s a system upgrade, not just an appliance swap — gas lines, venting, and electrical connections often need to be modified.
Sizing matters — tankless units are sized by gallons per minute (GPM), not gallons stored. Getting this wrong leads to cold water surprises.
Infrastructure upgrades are common — tankless units require far more BTUs than standard tanks, which often means upsizing your gas line.
Iowa’s hard water affects performance — mineral buildup in the heat exchanger is a real issue in the Des Moines area and requires annual maintenance.
The payoff is real — tankless units can be 24–34% more energy-efficient for average households and last up to 20 years, roughly twice as long as a traditional tank.
Permits are required — in Iowa, water heater replacements require permits and inspections regardless of the unit type.
Professional installation is essential — gas line work, venting changes, and code compliance are not DIY territory.

If your current water heater is aging, or you’re tired of running out of hot water when the whole household needs it at once, switching to tankless is worth a serious look. This guide covers everything you need to make a smart, informed decision — from sizing and infrastructure to maintenance and what the conversion process actually looks like.

Infographic: Tank vs Tankless switching overview showing efficiency, lifespan, sizing, and upgrade steps infographic

Switching from Tank to Tankless: What To Know About the Key Differences

Making the jump to on-demand hot water is exciting, but to understand if it is the right move for your home, you have to look closely at how these systems compare to traditional storage options. When we perform a Tankless vs Tank Water Heater Comparison, we look at several operational, physical, and financial differences.

To help you visualize the core differences, we have compiled this helpful comparison table:

Feature	Traditional Tank Water Heater	Tankless Water Heater
Average Lifespan	6 to 12 years	up to 20+ years
Energy Efficiency	Lower (Constant standby heat loss)	24% to 34% more efficient (for standard daily use)
Physical Footprint	Large (Takes up valuable floor space)	Compact (Wall-mounted, small footprint)
Risk of Water Damage	High (Stores 30–80 gallons that can leak/burst)	Minimal (No stored water to flood your home)
Hot Water Supply	Finite (Limited by tank capacity)	Endless (Continuous on-demand flow)

For a deeper dive into these systems, check out our Tankless Water Heaters: Complete Guide and learn why so many families find them to be Tankless Water Heaters: An Efficient Choice. Understanding How Long Does a Water Heater Last is a crucial first step in determining whether to repair your current unit or transition to a long-lasting tankless system.

Let’s break down these differences further by looking at the engineering under the hood.

Operational Mechanics and Energy Efficiency

A traditional tank water heater works on a simple principle: it heats a massive volume of water (typically 40 to 80 gallons) and keeps it hot 24 hours a day, 7 days a week. This constant cycle of heating and reheating is called “standby heat loss.” Even when you are asleep or away on vacation, your tank is burning fuel to keep that stored water hot. If you notice your energy bills climbing or hear strange rumbling sounds from your basement, these are common Signs Your Water Heater Is Going Out.

A tankless water heater, on the other hand, completely eliminates standby heat loss. It remains idle until you turn on a hot water tap. The moment water begins to flow, a flow sensor detects the movement and activates the heating source—either a high-powered gas burner or an electric element. The water travels through a tightly wound copper or stainless steel heat exchanger, warming up instantly to your target temperature before exiting the tap.

This difference in operation is reflected in the Uniform Energy Factor (UEF.) Traditional tanks usually have a UEF between 0.60 and 0.70, meaning 30% to 40% of the energy consumed is wasted. Modern tankless units can achieve UEF ratings up to 0.96, representing incredibly high thermal efficiency.

Furthermore, you have the choice between condensing and non-condensing tankless models:

Non-Condensing Units: These vent hot exhaust gases directly outside.

Because the exhaust is highly acidic and extremely hot, they require specialized, more expensive metal venting.
Condensing Units: These feature a secondary heat exchanger that captures heat from the exhaust gases to preheat the incoming cold water. This cools the exhaust significantly, allowing the use of inexpensive PVC venting and pushing the unit’s efficiency to its absolute peak.

Lifespan, Reliability, and Flood Risk Mitigation

Equipment longevity is one of the most compelling arguments for making the switch. A traditional tank water heater typically lasts between 6 and 12 years. Because they are constantly filled with water, the metal tank eventually succumbs to corrosive mineral deposits, leading to structural failure.

In contrast, a well-maintained tankless water heater can easily last 20 years or more. Because they do not store water, they are far less prone to the internal corrosion that destroys traditional tanks.

This brings us to a major safety benefit: flood risk mitigation. Nearly 75% of traditional tank water heaters will eventually leak or catastrophically burst at the end of their lifespan. When a 50-gallon tank ruptures, it doesn’t just stop at 50 gallons; the cold water supply line will continue to feed the leak until someone manually shuts it off. This can result in devastating property damage. Because tankless systems do not store water, the risk of a catastrophic basement flood is virtually eliminated.

Additionally, reclaiming physical space is a massive benefit. Traditional tanks take up a large footprint in your utility room, basement, or closet. Tankless units are compact, wall-mounted devices roughly the size of a carry-on suitcase. This allows you to reclaim valuable square footage for storage or living space. If you are preparing to make this transition, it is helpful to review the necessary Steps Before a Water Heater Replacement to ensure your home is ready.

Sizing and Infrastructure Requirements for Your Home

professional technician assessing home utility lines gas and electric

Switching to an on-demand system is not a simple “plug-and-play” task. Because tankless units heat water instantly, they have vastly different fuel, electrical, and venting requirements than traditional tanks.

Understanding How to Choose the Right Water Heater involves carefully calculating your home’s peak demand and evaluating your existing utility infrastructure.

Switching from Tank to Tankless: What to Know About Sizing Your System

When sizing a traditional water heater, you look at the storage tank’s capacity in gallons. With tankless systems, capacity is measured in Gallons Per Minute (GPM) and is heavily dependent on your local climate.

To size a tankless water heater correctly, we must calculate two primary factors:

Peak Demand (GPM): This is the maximum amount of hot water your household might use simultaneously. For example, if you want to run a shower while the dishwasher is running, you must add those flow rates together:
- Standard showerhead: 2.5 GPM
- Dishwasher: 1.5 GPM
- Peak Demand = 4.0 GPM
Temperature Rise: This is the difference between your incoming groundwater temperature and your desired output temperature (typically 120°F.)

This is where our local climate in Greater Des Moines plays a massive role. During our freezing Iowa winters, groundwater temperatures can drop into the low 40s. To heat that water to a comfortable 120°F, your water heater must achieve a 75°F to 80°F temperature rise.

Because the heating element must work much harder to warm freezing winter water, the maximum GPM output of a tankless unit decreases in the winter. A unit that easily delivers 7.0 GPM in the summer might only output 4.5 GPM in January. If your system is undersized, you will experience what we call a “cold water sandwich” or lukewarm showers when multiple fixtures are running.

To help you find the perfect system designed to handle cold Iowa winters, consult our Best Tankless Water Heaters Des Moines IA Guide and our Best Tankless Water Heaters West Des Moines Guide.

Switching from Tank to Tankless: What to Know About Infrastructure Upgrades

To heat water instantly, a tankless unit requires a massive, concentrated burst of energy. This means your home’s existing gas, electrical, and venting lines will almost certainly require modifications.

Gas Line Capacity: A standard gas tank water heater requires about 30,000 to 50,000 BTUs per hour. A whole-home gas tankless water heater, however, requires between 150,000 and 199,000 BTUs per hour to heat water on demand. Because of this massive jump in fuel demand, your existing 1/2-inch gas line will likely need to be upsized to a 3/4-inch or 1-inch line In some older homes, we may even need to coordinate with the local utility company to upgrade your gas meter.
Electrical Panel Amperage: Even gas tankless units require electricity to power their digital control boards, exhaust fans, and safety sensors. This usually requires installing a dedicated, grounded 120V outlet near the unit.

If you choose an electric tankless water heater, the electrical demands are extreme. A whole-home electric tankless unit can require 100 to 150 amps of dedicated power, which often necessitates a complete electrical panel upgrade to a 200-amp service.
Venting Modifications: Traditional tank heaters vent their exhaust naturally through a vertical metal flue that exits through your roof. Tankless units use combustion fans to actively push exhaust gases out of the home. Because of this positive pressure, you cannot use your old metal chimney flue. Non-condensing units require specialized Category III stainless steel venting, while high-efficiency condensing units can be vented horizontally through an exterior wall using affordable, dedicated PVC pipes.
Condensate Drainage: High-efficiency condensing units produce an acidic condensation (with a pH of 3 to 5) as they recapture heat from the exhaust. This liquid cannot be allowed to drip onto concrete floors or drain directly into standard metal pipes, as it will corrode them. We must install a condensate neutralizing kit and route a drain line to a nearby sump pump or floor drain.

Because of these complex requirements, maintaining strict Water Heater Code Compliance is essential. Every municipality in our service area has strict guidelines regarding fuel lines, electrical wiring, and exhaust clearances. To protect your safety and your home’s insurance coverage, we ensure all work aligns with Iowa Water Heater Code Requirements. If you are wondering, “Do I Need a Permit for Water Heater Replacement in Iowa?” the answer is a definitive yes—and our team handles the entire permitting and inspection process for you.

Water Quality, Maintenance, and Long-Term Performance

While tankless systems are incredibly reliable, they are not completely maintenance-free. In fact, because of the intense heat generated within their compact heat exchangers, they are highly sensitive to local water quality.

Hard Water Challenges in Iowa

The soil across Greater Des Moines is rich in limestone, meaning our municipal and well water supplies carry high concentrations of dissolved calcium and magnesium. This mineral content is measured in grains per gallon (GPG.) Any water reading above 7 GPG is classified as hard—and many areas in Iowa exceed this threshold significantly.

When hard water is rapidly heated inside a tankless unit, calcium carbonate precipitates out of the water and binds to the hot metal surfaces of the heat exchanger. This is known as mineral scaling.

Scale acts as an insulator.

It creates a physical barrier between the burner and the water, forcing your unit to work much harder and run hotter to achieve the same temperature. This results in:

A sharp drop in thermal efficiency
Inconsistent water temperatures
Overheating and premature failure of the heat exchanger

To understand how this process can damage your system, read about How Hard Water Shortens Water Heater Lifespan and explore the mechanics of Tankless Water Heater Scaling Problems.

To protect your investment in hard water areas, we highly recommend installing a whole-home water softener or a specialized scale inhibitor system. If you ever experience issues, our team is always here to help. You can read our Tankless Water Heater Repair Des Moines IA Guide or our Tankless Water Heater Repair Guide Ankeny IA for local support.

Routine Maintenance and Troubleshooting

To keep your system running at peak performance, annual maintenance is non-negotiable. This involves a process called descaling or flushing.

During an annual maintenance visit, we connect a portable pump to the service isolation valves on your tankless unit. We then circulate a food-grade descaling solution (or pure food-grade white vinegar) through the heat exchanger for about an hour. This solution safely dissolves and flushes out the accumulated calcium scale.

In addition to descaling, routine maintenance includes:

Cleaning the Flow Sensor: Mineral deposits or tiny debris can coat the flow sensor, preventing it from detecting water movement and stopping the burners from igniting.
Inspecting the Air Filter and Venting: We clear any dust, cobwebs, or outdoor debris from the intake filter and exhaust terminals to ensure proper combustion airflow.

Neglecting this maintenance can lead to system errors or a complete lack of hot water. If you notice your hot water fluctuating between hot and cold, look out for these Signs You Need Water Heater Repair. If you are currently dealing with a fluctuating system, our guide on why a Tankless Water Heater Inconsistent performance occurs can help you troubleshoot the issue.

Frequently Asked Questions About Tankless Conversions

Deciding to upgrade your home is a major step. To help you weigh your options, let’s address some of the most common questions homeowners ask when deciding Is a Tankless Water Heater Worth the Investment.

Will I have instant hot water at every tap with a tankless system?

This is one of the most common misconceptions about tankless systems. “On-demand” water heating means the unit creates endless hot water, but it does not mean the hot water arrives at your faucet instantly.

The “lag time” you experience is simply the time it takes for the standing cold water in your pipes to be pushed out so the newly heated water can travel from the water heater to your faucet. If your water heater is in the basement and your master bathroom is on the second floor, you will still have to wait for that water to make the journey.

To solve this issue, we can install:

Recirculation Pumps: Many modern tankless units feature built-in recirculation pumps that keep hot water loop-circulating through your pipes on a schedule or via smart sensors.
Point-of-Use Units: Installing a tiny, dedicated electric tankless unit directly under a distant bathroom or kitchen sink provides truly instantaneous hot water.

Do tankless water heaters work during a power outage?

No. Traditional gas tank heaters with standing pilot lights can operate without electricity, but all modern tankless water heaters require electrical power to run their control boards, electronic igniters, flow sensors, and exhaust blowers.

During a power outage, the gas solenoid valves inside the unit cannot open, meaning the system will not ignite. Fortunately, because their electrical draw is relatively low, you can easily run a gas tankless unit using a small battery backup (UPS) system or a portable generator to keep your hot water flowing during a storm.

How long does the tank-to-tankless conversion process take?

A straightforward, like-for-like traditional tank replacement usually takes about 2 to 4 hours. A tank-to-tankless conversion is a comprehensive system upgrade that typically takes 6 to 10 hours of professional plumbing and electrical work.

During this time, our technicians must drain and remove your old tank, mount the new unit, upsize your gas lines, run new PVC venting through your exterior walls, install condensate drains, and perform extensive safety and pressure testing. We always work efficiently to ensure your home’s water is turned back on as quickly as possible. If your water heater has failed unexpectedly and you need immediate help, refer to our Emergency Water Heater Installation Guide Ankeny IA.

Conclusion

Switching from a traditional tank to a modern tankless water heater is a fantastic way to enjoy endless hot water, reclaim valuable space in your home, and slash your monthly energy bills. However, because this transition involves specialized gas line work, precise GPM sizing for our cold Iowa winters, and strict code compliance, it requires professional expertise.

At True Comfort Heating, Cooling and Plumbing, we are proud to serve families across Greater Des Moines. Our licensed, bonded, and certified technicians are committed to treating you like family. We provide honest home assessments, dependable service, and flexible maintenance plans designed to keep your plumbing and HVAC systems running flawlessly year-round.

If you are ready to explore your options, we invite you to read our local guides:

Let us help you bring true, reliable comfort to your home. Schedule a consultation with our water heater experts today!