Imagine stepping into a shower during the morning rush and never worrying about the last person getting cold water. That’s the promise of a modern tankless water heater: hot water on demand, only when you need it, for as long as you need it. For homeowners who want comfort without waste, a tankless water heater can be a game-changer—delivering efficiency, space savings, and long-term reliability in a sleek package.
Written on behalf of MACKAY Heating & Cooling, this in-depth guide explains how a tankless water heater works, why it’s different from a storage tank, what sizing really means, and how to plan an installation that fits your home and lifestyle. You’ll learn the practical pros and cons, the real costs, and the maintenance that keeps performance high for years. By the end, you’ll know whether a tankless water heater is the right upgrade—and how to make the switch confidently.
What Is a Tankless Water Heater (and Why It Caught On)
A tankless water heater is a compact appliance that heats water only when a fixture opens, instead of storing 40–60 gallons in a big, always-hot tank. When you turn on a tap, a flow sensor triggers powerful burners (gas) or heating elements (electric) to raise the water temperature instantly as it moves through a heat exchanger. When you close the tap, the unit shuts off—no standby losses, no keeping a tank warm all day.
The big shift in mindset
- From storage to demand: With a tank-based system, you’re constantly reheating a large volume whether you use it or not. With a tankless water heater, you pay to heat water only when someone is using it.
- From “how much is stored?” to “how much per minute?” Sizing a tank focuses on volume. Sizing a tankless water heater focuses on flow rate (litres/minute or gallons per minute, GPM) at your chosen temperature rise.
How a Tankless Water Heater Works (Step by Step)
- A tap opens. Flow passes a sensor inside the unit.
- Heating begins. A gas burner ignites or electric elements energize.
- The heat exchanger transfers energy. Water absorbs heat as it travels through narrow pathways designed for maximum contact.
- Temperature is regulated. The control board modulates flame or current to hit your setpoint (often 49–55 °C / 120–131 °F).
- Tap closes; unit rests. The tankless water heater shuts down to standby with negligible energy use.
Why modulation matters
Unlike fixed-output appliances, a tankless water heater modulates (ramps up or down) based on the flow you demand. One bathroom faucet at 1.0 GPM? Low output. Two showers and a dishwasher? The unit scales up automatically—within its rated capacity.
The Top Benefits of Going Tankless
Truly endless hot water
With a correctly sized tankless water heater, back-to-back showers, laundry, and dishwashing can happen without running the tank empty. It’s “time-based” freedom: hot water for as long as you need it, provided your total flow doesn’t exceed the unit’s capacity.
Energy efficiency (no standby losses)
Storage tanks lose heat through their walls 24/7 and must reheat even when no one is home. A tankless water heater avoids that waste and can significantly reduce fuel consumption—especially in smaller households or those with sporadic hot water use.
Space savings
Most wall-hung units are about the size of a suitcase. Swapping to a tankless water heater frees floor space for storage, a utility sink, or just cleaner mechanical rooms.
Longer service life
A quality tankless water heater can last 15–20 years with basic maintenance, often outliving a typical tank by many seasons. Many parts are modular, so repairs can be targeted rather than full replacements.
Cleaner, fresher hot water
Because there’s no large reservoir sitting at warm temperatures, a tankless water heater reduces the risk of stale water issues. With proper maintenance, scale build-up is managed proactively rather than accumulating in a tank.
The One Caveat: Capacity Is About Flow and Temperature Rise
To choose the right tankless water heater, you must match your simultaneous demand and your local inlet temperature to the unit’s flow capacity.
Flow rate basics
- Shower: ~1.5–2.5 GPM (5.7–9.5 L/min) depending on the head
- Bathroom faucet: ~0.5–1.0 GPM (1.9–3.8 L/min)
- Kitchen faucet: ~1.0–2.0 GPM (3.8–7.6 L/min)
- Dishwasher/washing machine: varies by model
Temperature rise
If your incoming water is 7 °C (45 °F) and you want 49 °C (120 °F) at the tap, the tankless water heater must deliver a 42 °C (75 °F) rise at the flow you’re using. Colder regions require larger or multiple units to support many fixtures at once.
A quick example
You want two 2.0 GPM showers and a 1.0 GPM sink running together (5.0 GPM total) with a 40–45 °C temperature rise. Look for a tankless water heater that supports at least 5.0 GPM at that rise (not just its max flow at ideal lab conditions). MACKAY Heating & Cooling runs this math for you and recommends right-sized models—not just the biggest or cheapest option.
Gas vs. Electric: Which Tankless Water Heater Fits Your Home?
Gas-fired (natural gas or propane)
- Pros: High output in a compact unit; great for whole-home use; wide model availability.
- Considerations: Requires proper venting (often stainless or PVC, depending on model), gas line capacity, combustion air supply, and condensate handling for condensing units.
Electric
- Pros: Simpler installation (no gas/venting), strong for point-of-use or small homes, useful where gas isn’t available.
- Considerations: Whole-home models may demand substantial electrical capacity (multiple high-amp breakers). Your panel may need upgrading to handle a powerful electric tankless water heater.
Installation Essentials: What Pros Look For
A smooth, code-compliant installation is the difference between “works on day one” and “works beautifully for 20 years.”
Gas line sizing and venting
A gas tankless water heater often needs larger gas supply than a tank. Venting must meet length, material, and termination rules. Condensing units produce acidic condensate that must be neutralized before drain disposal.
Water quality and scale
Hard water leads to scale on heat exchanger surfaces. A tankless water heater with an isolation valve kit and a simple descaling plan keeps efficiency high. In very hard-water areas, consider a treatment system.
Condensate management
High-efficiency gas models create condensate. Routing, neutralizing, and safely draining it is part of a clean install.
Recirculation options
If some taps are far from the mechanical room, a recirculation loop or a smart demand pump can deliver near-instant hot water, reducing wasted water and time. Modern controls can pair with a tankless water heater to run recirculation only when needed.
Ongoing Care: Maintenance for a Long, Efficient Life
A little preventive work each year keeps performance high.
- Annual flush/descale (frequency depends on water hardness and usage).
- Clean inlet water screen and check isolation valves.
- Inspect venting for integrity and proper slope.
- Test condensate neutralizer and clear drain lines on condensing gas units.
- Update controller firmware where supported; verify setpoint and safety parameters.
MACKAY Heating & Cooling offers simple maintenance plans tailored to your tankless water heater, water quality, and usage patterns.
Performance in Real Homes: Where Tankless Shines
Busy mornings, overlapping showers
A correctly sized tankless water heater keeps showers hot without rationing. No one gets the “cold surprise” because a tank ran out.
Extended soaks and back-to-back baths
Long tubs or jetted baths draw a lot of hot water. A tank-based heater can empty halfway through; a tankless water heater keeps filling until you’re done.
Compact or renovated spaces
If you’re reclaiming a tight mechanical room, a wall-hung tankless water heater frees floor area and cleans up the layout.
Vacation homes and intermittent use
Why heat water 24/7 for an empty cottage? A tankless water heater uses energy only on arrival and during stays.
Cost and ROI: What to Expect
Upfront investment
A quality tankless water heater typically costs more to install than a basic tank, especially if gas lines, electrical service, or venting need upgrades. But for many homes, these are one-time costs that open the door to decades of efficient on-demand comfort.
Operating savings
Eliminating standby losses is the big win. A tankless water heater can cut energy use notably in households with variable demand. Add recirculation controls and low-flow fixtures and savings add up.
Longevity and serviceability
Parts often are modular and accessible, and a tankless water heater is built for repair rather than discard. Over a 15–20-year life, that can mean better total value than multiple tank replacements.
For neutral Canadian guidance on water heating and home energy efficiency, see:
Natural Resources Canada – Water Heating basics
NRCan – Heating, Ventilation and Air Conditioning overview
Common Myths (and the Real Story)
“They don’t work in cold climates.”
Modern units are designed to handle low inlet temperatures. You simply size a tankless water heater for the required temperature rise and simultaneous flow—or install tandem units for large homes.
“They can’t keep up with two showers.”
A properly sized tankless water heater can. Mismatch occurs when units are chosen by “max GPM” only, rather than GPM at your local temperature rise.
“Maintenance is complicated.”
Yearly flushing and a quick screen check are simple. With isolation valves, a tankless water heater is easier to descale than many tank coils.
Sizing 101: A Simple Path to the Right Unit
- List your simultaneous fixtures at peak time (e.g., two showers + one sink).
- Add their GPM at your preferred flow settings.
- Find your winter inlet temperature and calculate temperature rise to your setpoint.
- Match the performance table: choose a tankless water heater that delivers your GPM at that rise, with a little headroom.
MACKAY Heating & Cooling handles this entire process—plus gas, venting, electrical, and recirculation design—so the system performs as promised on the coldest days.
10 Smart Upgrades That Pair Well with Tankless
- Low-flow showerheads (comfortably 1.75–2.0 GPM)
- Demand-controlled recirculation pump
- Descaling isolation valve kit
- Condensate neutralizer (condensing gas models)
- Whole-home leak detector and automatic shutoff valve
- Scale treatment for hard water regions
- Smart controller with vacation/anti-freeze modes
- Mixing valve at the outlet for safer, stable temperatures
- Dedicated combustion air supply (for sealed-combustion gas)
- Insulated hot-water lines to reduce lag and losses
Environmental Angle: Comfort That’s Also Responsible
A tankless water heater can reduce wasted energy by eliminating standby heating. When paired with low-flow fixtures and smart recirculation, it also trims water waste from long waits at distant taps. Over time, that means fewer emissions and a smaller footprint—all while making daily life easier.
The Installation Day Experience (What We Do, What You’ll See)
- Pre-visit planning: We confirm gas/electric capacity, vent routes, drain options, and mounting locations.
- Clean removal of the old tank and safe handling of any remaining water.
- Precise mounting and connections for gas/electric, water, venting, and condensate.
- Commissioning: We test combustion/amp draw, verify temperature rise at multiple flows, and set recirculation logic if applicable.
- Owner orientation: We show you how to set temperatures, use any smart features, and perform quick screen cleaning.
- Documentation: You get a photo-rich report with model/serials, settings, and warranty registration details.
Why Choose MACKAY Heating & Cooling
Choosing a tankless water heater is part technology, part design. MACKAY Heating & Cooling brings both to your project. We size based on your real usage, winter inlet temps, and fixture mix; we check gas and electrical capacity, vent lengths, and condensate plans; and we commission the unit with measured data—not just a quick hot/cold test. You get clear options (good/better/best), transparent pricing, and a maintenance plan you can actually follow. If you want a tankless water heater that stays quiet, efficient, and dependable for the long haul, we’ll make that simple.
Where One Unit, Two Units, or Point-of-Use Wins
- One high-capacity unit: Ideal for small to mid-size homes with typical simultaneous demand (two showers + one sink).
- Two smaller units in parallel: Great for large families or homes with luxury tubs and multiple showers running together.
- Point-of-use electric under a distant sink: Perfect for a back bathroom or studio where a whole-home tankless water heater would be overkill.
Troubleshooting Snapshot: If Hot Water Seems Inconsistent
- Check your aerators and showerheads: Flow restrictors can reduce flow below the unit’s minimum activation rate; cleaning them often fixes “short-cycling.”
- Verify setpoint: Many units ship with conservative default settings (e.g., 49 °C).
- Look for partial scale: If flow has dropped over time, descaling your tankless water heater may restore performance.
- Call if you smell gas or see error codes: These require a licensed technician.
Comfort on Demand—For Years to Come
When you’re ready to stop scheduling showers around a tank and start enjoying true on-demand comfort, a tankless water heater is a smart, modern answer. Done right, it delivers endless hot water, lower energy waste, a smaller footprint, and a mechanical room that finally makes sense. If you’re considering the switch, connect with MACKAY Heating & Cooling. We’ll size it correctly, install it cleanly, and keep it dialed in with simple annual care—so your hot water is just there, every time you need it.
Frequently Asked Questions
1) Will a tankless water heater really give me endless hot water?
Yes—within its flow capacity. With proper sizing, a tankless water heater can supply continuous hot water for back-to-back showers, long soaks, and laundry without running out.
2) Is a tankless water heater more efficient than a traditional tank?
Typically, yes. By eliminating standby losses, a tankless water heater heats only what you use, when you use it—often reducing overall energy consumption.
3) Can a tankless water heater handle two showers at once?
A correctly sized tankless water heater can support multiple fixtures at once. We calculate your simultaneous flow and temperature rise to select the right model or combination.
4) What maintenance does a tankless water heater need?
Annual flushing/descaling (frequency depends on water hardness), cleaning inlet screens, checking venting and condensate, and verifying settings. With simple care, a tankless water heater stays efficient for many years.
5) Do I need to upgrade my gas line or electrical panel for a tankless water heater?
Sometimes. Gas units may need larger gas supply and proper venting; whole-home electric units may need additional electrical capacity. We verify these during the estimate.
6) Will a tankless water heater save me money?
Savings vary with usage. Many households see lower bills from eliminating standby losses. Over time, the longer service life and repairability of a tankless water heater can improve total cost of ownership.
7) How do I pick the right size tankless water heater?
List the fixtures you’ll use at the same time and your desired water temperature. We match that flow to your local inlet temperature to recommend a tankless water heater that meets your needs with a bit of headroom.
