🔥 FL Tankless Water Heater Sizing

Calculate peak GPM demand, BTU input, and temperature rise using Florida's 60–76°F groundwater temperatures. Size gas or electric tankless units correctly for FL's unique conditions

FL GROUNDWATER 60–76°F

Flow Rate

Unit Sizing

FL Guide

Quote

🚿 Peak GPM Demand Calculator

Enter the quantity of each hot-water fixture. Peak demand = simultaneous use (e.g., 2 showers + dishwasher running at once).

🚿 Standard Shower (2.0 GPM) 2.0 ea

🌧️ Rainfall Shower Head (3.0 GPM) 3.0 ea

🛁 Garden / Soaking Tub Fill 4.0 ea

🍽️ Kitchen Faucet (1.8 GPM) 1.8 ea

🪥 Bathroom Faucet (1.0 GPM) 1.0 ea

🥗 Dishwasher (0.7 GPM) 0.7 ea

👕 Clothes Washer (2.0 GPM) 2.0 ea

🪣 Utility / Mop Sink (1.5 GPM) 1.5 ea

All fixtures simultaneous

4.5 GPM

Realistic peak (75%)

3.4 GPM

Adjust fixture quantities above — results update automatically.

💡 Sizing Philosophy: Simultaneous Use

Low (1–3 GPM): 1 shower + kitchen faucet. Studio, condo, or 1BR apartment.

Moderate (3–5 GPM): 2 showers + dishwasher. Standard FL 3BR/2BA home — most common sizing range.

High (5–8 GPM): 2+ showers + tub fill + dishwasher. Larger home, master bath with rainfall head.

Very High (>8 GPM): Multiple showers + heavy commercial use. Two units or a commercial-grade system.

FL tip: Clothes washers rarely run on hot in Florida's warm climate — most FL residents use cold wash year-round. Don't oversize for the washer unless it's specifically used for hot cycles.

📊 BTU / kW Unit Sizing Calculator

FL Region (Sets Groundwater Temperature) Desired Hot Water Output Temperature Fuel Type Peak GPM (from Flow Rate tab, or enter manually)

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Temp Rise (°F)

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BTU/hr Output

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BTU/hr Input

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kW Equiv.

Matching Units

🌡️ FL Groundwater Temperature Advantage

Why FL is ideal for tankless: Florida's warm groundwater (60–76°F year-round) means far less temperature rise than cold-climate states (40–50°F groundwater). A unit rated for 5 GPM in Minnesota may handle 8+ GPM in South FL at the same BTU input.

No seasonal penalty: Unlike northern states where groundwater drops to 40°F in winter and forces oversizing, FL groundwater stays nearly constant year-round. The unit you size for summer is the unit you need in January.

FL Region	Groundwater	ΔT to 110°F	vs. Northern ΔT
South FL	76°F	34°F	48% less BTU
SW FL	75°F	35°F	46% less BTU
Central FL	72°F	38°F	40% less BTU
Space Coast	70°F	40°F	36% less BTU
NE Florida	67°F	43°F	31% less BTU
N Central FL	63°F	47°F	24% less BTU
Panhandle	60°F	50°F	20% less BTU
Northern US	40°F	70°F	Baseline

⚠️ #1 FL Issue: Hard Water Scale Buildup

Florida's hard water (6–22 GPG) is the leading cause of premature tankless water heater failure in FL. Without treatment, scale can reduce heat exchanger efficiency 20–40% per year and void manufacturer warranties in 2–3 years.

Why tankless units are vulnerable: The heat exchanger in a tankless unit has narrow channels (some under 1/16" wide) that concentrate mineral deposits. Unlike a tank water heater where scale sinks to the bottom, in tankless units it coats the heat exchanger directly — the highest-heat area. At 15+ GPG, visible scale can build within 6–12 months.

Scale protection options (FL-specific):

• Annual descaling flush (minimum): $125–$250/year service call. White vinegar or citric acid flush circulated through the heat exchanger. Required in most FL counties to maintain warranty.

• Polyphosphate scale inhibitor filter: $75–$200 installed, $40–$80 cartridge every 6 months. Low cost, reduces (doesn't eliminate) scale. Good for moderate hardness (<14 GPG).

• Electronic/magnetic scale inhibitor: $200–$500 installed. No salt, no waste water. Effective for hardness under 16 GPG. Reduces crystal size but doesn't eliminate minerals.

• Water softener (best protection): $800–$2,500 installed. Eliminates scale entirely via ion exchange. Required by Navien, Noritz, and some Rinnai models to maintain warranty in FL. See our Water Softener Sizing tool for FL-specific sizing.

FL County	Hardness	Scale Risk	Recommendation
Collier	22 GPG	Extreme	Softener required
Lee	20 GPG	Extreme	Softener required
Miami-Dade	19 GPG	Very High	Softener required
Broward	17 GPG	Very High	Softener required
Palm Beach	15 GPG	High	Softener recommended
Sarasota	14 GPG	High	Softener recommended
Hillsborough	13 GPG	High	Scale inhibitor minimum
Orange / Orlando	8 GPG	Moderate	Annual descale
Brevard	10 GPG	Moderate	Scale inhibitor or descale
Duval	6 GPG	Low	Annual descale only

📋 FL Code & Permit Requirements

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Gas tankless units must use sealed combustion (direct vent) or power vent. Open-combustion gas appliances require combustion air provisions rarely available in FL airtight homes. 2023 FBC § 501.7 / NFPA 54 Ch. 10

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Permit required for all water heater replacements in FL, regardless of fuel type. Homeowner permit available in most counties for single-family residential — ask us about permit-pull service. FL Statute 489.103(7)(a)

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Gas water heaters must meet minimum 0.82 Energy Factor. Condensing tankless units (0.94–0.98 EF) exceed this significantly — qualifying for FPL / Duke Energy rebates in FL. FL Energy Code § R404.1

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CSST flexible gas pipe serving tankless units requires arc-fault bonding per 2023 FBC. Bonding wire must run to electrical ground panel within the same room. 2023 FBC / NFPA 54 § 7.13

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T&P relief valve discharge pipe must terminate within 6" of floor or to outside. Condensing units produce acidic condensate — drain must comply with FPC neutralization requirements. FPC § 504.6

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Electric tankless units (24–36 kW) require dedicated 240V circuits — 100A to 150A. Confirm main panel capacity (most FL homes have 150A or 200A service) before purchasing. NEC 422.11 / FBC Electrical

⚡ Gas vs. Electric in Florida

Factor	Gas Tankless	Electric Tankless
Unit cost	$600–$1,800	$250–$700
FL install cost	$800–$2,200	$400–$1,200
FL annual energy cost	~$220–$350/yr	~$400–$650/yr
Max flow rate	4–11 GPM	2–4 GPM
Hurricane outage	Works (battery pilot)	No hot water
Scale sensitivity	Moderate	Higher (element coils)
Lifespan	20–25 years	10–15 years
Best for	Whole-house	Point-of-use / supplement

Gas tankless pays back the higher install cost in 3–5 years vs. electric in FL, assuming FPL average rates of $0.14–$0.16/kWh and natural gas at ~$1.20/therm.

💰 FL Installation Cost Reference (2024–2025)

Item	Low	High
Gas tankless unit (condensing)	$900	$1,800
Gas installation labor (FL)	$800	$2,200
Gas supply line upgrade	$400	$1,500
Electric tankless unit	$250	$700
Electric installation (FL)	$400	$1,200
Panel upgrade (if needed)	$1,200	$3,500
Water softener (recommended FL)	$800	$2,500
Scale inhibitor filter	$150	$400
FL permit (typical)	$75	$350
Annual descaling service	$125	$250

📞 Free Tankless Water Heater Quote

All installations include FL permit, water hardness test, scale-protection recommendation, and 1-year labor warranty.

Your Name Phone Number City / County Current Water Heater Type Fuel Preference Number of Bathrooms Additional Notes (optional)

✅ Why Choose Us

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FL-licensed plumbing contractor (CPC) — every job fully permitted

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Free water hardness test with every quote — we protect your investment

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All major brands: Rinnai, Navien, Noritz, Rheem, Bradford White

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Gas line sizing and upgrade included — one company, one call

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Annual descaling service plan — protects manufacturer warranty

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Same-day service available throughout South and Central FL