Are Two Small Tankless Water Heaters Better Than One Big One?

Are Two Small Tankless Water Heaters Better Than One Big One?

In the quest for efficient and consistent hot water supply in homes, tankless water heaters have become popular. They are known for their energy efficiency and the ability to provide hot water on demand. However, homeowners often face a dilemma when choosing between installing two small tankless water heaters or one big one. This article explores the pros and cons of each option to help you make an informed decision.

Before diving into the comparison, it’s essential to understand how tankless water heaters work. Unlike traditional water heaters that store and preheat water in a tank, tankless heaters heat water directly as it flows through the device. This on-demand heating means you’re not wasting energy on heating water you’re not using, making it an energy-efficient choice for many households.

One Big Tankless

Imagine a single, sleek unit that delivers endless hot water on demand. That’s the promise of a big tankless water heater. It boasts a high flow rate, meaning it can simultaneously handle multiple hot water demands, perfect for large families or homes with multiple bathrooms. Plus, its compact size saves valuable space compared to traditional tank water heaters.

The case for one big tankless water heater:

  1. High Capacity: A larger unit can handle a higher simultaneous demand for hot water. This is particularly beneficial in larger households where multiple hot water outlets are often used simultaneously.
  2. Cost-Effective Installation: Installing one big unit is typically less complex and can be more cost-effective than setting up two separate systems, considering the need for only one set of installation materials and labor.
  3. Space Efficiency: A single larger unit generally takes up less space than two smaller ones. This can be a crucial factor in homes where space is premium.
  4. Maintenance: Maintaining one unit is generally simpler and potentially less expensive than maintaining two. With only one system to service, you save time and potentially reduce the overall maintenance costs.

Two Small Tankless

Think of two smaller tankless water heaters as a team of hot water ninjas. For lightning-fast delivery, they’re strategically placed near your main hot water usage points, like the kitchen and bathrooms. This setup minimizes heat loss in long pipe runs, saving you money and energy.

The case for two small tankless water heaters:

  1. Flexibility in Installation: Small tankless water heaters offer more flexibility in installation. You can place them closer to the point of use, reducing the time and energy lost in the transit of hot water through the pipes. This setup ensures that hot water is available faster when you turn on the tap.
  2. Targeted Heating: You can target the heating more efficiently with two units. For example, one unit can be dedicated to the bathrooms, while the other serves the kitchen and laundry. This targeted approach ensures that the demand for hot water in one part of the house doesn’t affect the supply in another.
  3. Redundancy: Having two units means you have a backup if one fails. You won’t be left without hot water while waiting for repairs.
  4. Potential Energy Savings: Two smaller units can be more energy-efficient if your hot water usage patterns are variable. You can turn off or lower the temperature of one unit when it’s not needed, reducing energy consumption.

Two Small Tankless vs. One Big One – Factors to Consider

When deciding between two small or one big tankless water heater, consider the following factors:

Hot Water Demand

Assess your household’s hot water needs. A larger unit might serve you better if you have a high simultaneous demand. Two smaller units might be more efficient if your hot water usage is more scattered or localized.

Usage Patterns

Consider when and how you use hot water. If different areas of your home have distinct hot water usage patterns, the targeted heating of two units could offer energy savings.

Space and Installation Constraints

Evaluate the space available for installation and any installation constraints you might face. Two smaller units might offer more flexibility but require more complex plumbing.


Consider both the upfront installation costs and the long-term operating costs. Two units might offer savings in energy consumption but could have higher installation and maintenance costs.

Resale Value

Think about the potential impact on your home’s resale value. Some buyers might appreciate the redundancy and targeted heating of two units. In contrast, others might prefer one large unit’s simplicity and high capacity.

One Big Tankless vs. Two Small Tankless: Pros and Cons

Like most things in plumbing, the answer isn’t one-size-fits-all. It largely depends on your specific needs, preferences, and household dynamics. If you’re grappling with the decision between a single large or two smaller tankless water heaters, understanding the contexts in which each option excels can guide you to a choice that best aligns with your requirements.

Here’s a breakdown to ease your decision-making process:

Choose a single big tankless if:

  • You have a large household with high hot water demand.
  • You have plenty of space for installation.
  • You prioritize a high flow rate over energy efficiency.
  • You’re willing to invest in a higher upfront cost.

Choose two small tankless if:

  • You want faster hot water delivery and reduced energy waste.
  • You have limited space for a single unit.
  • You value redundancy and peace of mind.
  • You’re comfortable with a slightly higher total cost.
FeatureOne Big TanklessTwo Small Tankless
Flow RateHighLower per unit, but combined flow can be similar
Space RequirementsCompactRequires space for two units near usage points
Energy EfficiencyHighly efficientEven more efficient due to less heat loss in pipes
Upfront CostHighHigher total cost due to two units
Installation ComplexityModerateMore complex due to installation of two units
Warranty CoverageMay be shorter for larger unitsStandard warranty for each unit
RedundancyNoOne unit failing won’t affect the other
Ideal forHigh hot water demand, large families, multiple bathroomsFaster hot water delivery, energy efficiency, limited space for single unit

Choosing between two small tankless water heaters and one big one depends on various factors, including your household’s hot water needs, usage patterns, space considerations, budget, and personal preferences. Carefully weigh the pros and cons, and consider consulting with a professional plumber to assess your specific needs and make the most suitable choice for your home.

Ultimately, whether you opt for two small tankless water heaters or one big one, the goal is to ensure a consistent, energy-efficient, cost-effective hot water supply for your home. With the right choice, you can enjoy the comfort and convenience of hot water on demand, tailor-made to suit your household’s unique requirements.

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