One Tank, Two Jobs? Why Using a Water Heater for In-Floor Heat and Domestic Water is Asking for Trouble

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A lot of homeowners in Okotoks and the Foothills are surprised to learn that their hot water tank is pulling double duty — supplying both domestic hot water (for taps and showers) and in-floor heating for their home or garage.

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Sounds smart, right? One system doing everything?

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Not quite. At Project Heating and Plumbing, we’ve seen firsthand why this “one-tank-fits-all” approach leads to problems, inefficiency, and expensive failures.

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Let’s break down why combining your heating and domestic water in a single tank isn’t the upgrade it seems — and why separating the two is the smart move.

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The Problem with a Combo Water Heater Setup

1. Temperature Conflicts

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• Domestic hot water should be delivered at ~120°F (safe for skin)
• In-floor radiant systems often need ~90–130°F depending on design
• When one tank tries to supply both, it often ends up too hot for taps or too cold for the floor — never doing either job right.

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Result?
Poor comfort in winter and the risk of scalding at the tap.

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2. No Flow Priority = Cold Showers

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In-floor heating systems use slow, continuous circulation, especially in colder months. This means the water heater is constantly “on duty” maintaining floor temps.

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When someone turns on the shower, the tank may already be low on heat — leading to cold water at the worst time.

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Hint: If your shower runs cold every time the floor heat kicks in, this is why.

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3. Shortened Equipment Life

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Water heaters aren’t designed to run 24/7. When used for space heating:

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• Burners cycle more often
• Heat exchangers wear faster
• Recovery time increases
• Tanks fail prematurely
• A 6-year tank doing double duty might only last 3–4 years, especially if water quality isn’t perfect.

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4. Bacteria Risk (Seriously)

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If floor heating loops aren't properly isolated or treated, stagnant water can mix with domestic water. That creates an ideal breeding ground for legionella and other harmful bacteria.

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Proper systems separate potable water from closed heating loops — no risk of contamination.

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Why You Should Separate Domestic Hot Water from Hydronic Heating

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Installing dedicated systems for each job means:

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• 💧 Stable hot water for showers, taps, and appliances
• 🔥 Consistent heating across your floor zones
• 🧰 Longer equipment life and fewer emergency calls
• ☑️ Safer and up to current code
• 💸 Lower operating cost when sized properly
• We typically recommend:

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• A condensing boiler for radiant/hydronic floor heat
• A separate tank-style or on-demand water heater for domestic use
• Each does what it’s meant to do — efficiently and reliably.

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Real Talk from the Field

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We’ve replaced dozens of combo water heater systems across Okotoks, Dewinton, and the Foothills. Many were less than 5 years old, constantly failing or causing hot water complaints.

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In every case, splitting the system solved the issue — and delivered better comfort and reliability.

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Ready to Do It Right?

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If you’re running both your in-floor and domestic hot water off one tank, or thinking about installing a new system, let’s chat. We’ll design a setup that works smarter, lasts longer, and keeps your home safer.

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📍 Based in Okotoks | Serving the Foothills & Beyond
📞 403-601-5387
💻 projectheating.ca

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Project Heating and Plumbing — When it comes to radiant heat and hot water, we don’t cut corners. We build systems that work.

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