Choosing the wrong solar water heater drains an Ontario off-grid battery bank before breakfast. A homeowner on Edinburgh Road South in Guelph learned this when his 9kW electric tankless commissioned. His Tier 2 system was correct: 200Ah LFP at 24V, 600W array, Victron MPPT, 3000W inverter. Two 8-minute showers at 1800W modulated flow consumed 480Wh from the bank.
His January array produced 720Wh on a clear day at 1.5 peak sun hours. Morning showers consumed 480Wh before 9 AM, leaving 240Wh for fridge, Starlink, and lights. On overcast January days the array produced only 100 to 200Wh. The morning showers swallowed that entire budget before any other load ran.
I reviewed the corrected system in March 2024. He had replaced the electric tankless with propane on-demand. The new draw was 1W for ignition and 15W for the control board. The Victron SmartShunt logs showed the bank stable at 80 to 95% SoC every morning.
The verdict was settled: propane for year-round Ontario hot water, with solar thermal as a summer supplement. See our Ontario solar sizing guide before designing any solar water heater into your budget. The pillar reference is our off-grid living guide.
| System | Cost installed | Battery draw | Winter performance | Ontario verdict |
|---|---|---|---|---|
| Propane tankless 40,000 to 150,000 BTU | $350 to $1,500 | 1 to 25W (control board only) | Excellent, rated to -42C | Year-round standard |
| Solar thermal evacuated tube + glycol | $3,000 to $8,000 | 50 to 100W (circulation pump) | Needs propane backup Nov to Apr | Summer supplement only |
| Electric on-demand 1,200 to 9,000W | $200 to $1,200 | 240Wh per shower minimum | Drains Tier 2 bank by 9 AM | Tier 3 systems only |
Solar water heater Ontario: the three options compared
Three solar water heater paths exist for Ontario off-grid properties: propane tankless, solar thermal, and electric on-demand. Only one is correct year-round below Tier 3 capacity. The other two have specific use cases. Neither covers primary winter hot water on a battery-based system.
Propane tankless delivers instant unlimited hot water at 1 to 25W of battery draw. Ontario well water at 5 to 10C in January is handled instantly at any ambient temperature. Solar thermal covers 80 to 100% of summer hot water from May through September. It needs propane backup the rest of the year.
Electric on-demand at 1800W consumes 240Wh per shower, half a 100Ah LFP bank by 9 AM. See our off-grid shower guide for the full shower-specific energy breakdown.
How an electric tankless empties a Tier 2 bank before 9 AM
The Edinburgh Road failure mode is the most common solar water heater mistake on Ontario off-grid properties. Electric tankless units rated 6000 to 9000W draw 500A or more at 12V. A 200Ah LFP bank at 24V holds 3,840Wh of usable capacity. Two morning showers consume 480Wh before any other load runs.
The second failure mode catches some installers entirely off guard. A 6000W electric tankless on a 3000W PSW inverter trips the inverter on startup surge. The inverter is rated 3000W continuous and 6000W surge for fractions of a second only. A six-minute hot shower trips it before water reaches body temperature.
Edinburgh Road avoided this only because the 9kW unit modulated down to 1800W on low flow. A direct 6000W call would have tripped the inverter on the first attempt. Think of it like cranking a diesel truck with a motorcycle battery. The cranking amps are not there for even one revolution.
The Edinburgh Road outcome was correctable because his bank was sized for intelligent loads. After the propane swap his 600W array produced 720Wh on clear January days. Total daily intelligent load was about 510Wh, leaving real reserve for grey streak periods. The same system with electric tankless installed would have hit BMS cutoff every overcast day.
Propane tankless: the year-round solar water heater standard for Ontario
A propane tankless solar water heater delivers unlimited hot water at $0.15 to $0.30 per shower. Ontario well water at 5 to 10C in January is handled instantly. Battery draw is 1W for ignition and 10 to 25W for the control board. TSSA-licensed gas fitters are mandatory for all permanent propane connections in Ontario.
Two unit sizes cover most Ontario off-grid properties. A 40,000 BTU on-demand unit at $350 to $500 fits 1 to 2 person seasonal cottages. A 150,000+ BTU whole-home unit at $800 to $1,500 handles 3 to 5 person permanent residences. Both units pass the SmartShunt test at 1 to 3W during any hot water use.
A property owner in Elora, Centre Wellington specified propane on-demand from day one. His SmartShunt confirmed 1 to 3W during every hot water use through two full Ontario winters. “We’ve never once thought about the hot water since we moved in,” he said. Family of 4, unlimited hot water, zero battery bank impact.
The battery ignition point is the detail most installations miss. A propane tankless needs reliable battery supply for electronic ignition and the control board. In an unheated Ontario utility room at -20C, a standard LFP refuses charge on cold mornings. The ignition circuit then cannot fire and the household has no hot water.
A Battle Born heated LFP battery in the utility room maintains charge acceptance to -20C ambient. The ignition circuit is then always powered regardless of utility room temperature. See our propane generator guide for the shared propane supply sizing approach.
Solar thermal: free hot water May through September with the glycol rule
A solar thermal system provides free domestic hot water during Ontario’s productive solar season. Flat plate or evacuated tube collectors with a 200 to 300L tank cover 80 to 100% of summer hot water. A cottage owner on Guelph Line in Burlington added a solar thermal flat plate system in spring 2023. Her installed cost was $3,800.
From Victoria Day through Thanksgiving the system provided 85% of her hot water requirements. She saved $180 to $190 per season in propane costs. She winterized the glycol loop in late October each year. Three seasons in, no freeze damage, no service interruption.
The glycol mandatory rule has zero exceptions. A closed-loop propylene glycol and water mixture must circulate through the collectors. Plain water in outdoor solar thermal collectors freezes on the first Ontario night below -5C. The vacuum tubes shatter or the flat plate channels burst.
A 50% glycol mix provides freeze protection to approximately -35C, covering every Ontario winter temperature. Annual glycol testing and top-up takes 30 minutes and costs $20 to $40. For seasonal Ontario properties, drain the entire loop in October and recommission in May. See our solar battery guide for the circulation pump load math.
Sizing the right system for your Ontario household
Sizing the right solar water heater for an Ontario household means matching output to occupancy and season. For 1 to 2 person seasonal cottages, a 40,000 BTU propane tankless at $350 to $500 is correct. A 100 to 150L solar thermal storage tank with a single collector also works for that household size. For 3 to 5 person permanent residences, a 150,000+ BTU whole-home propane unit handles simultaneous draws.
Solar thermal for a 3 to 5 person household requires 300 to 400L of storage. It also needs 4 to 6 square metres of collector area for 70 to 85% annual coverage. Ontario Building Code Section 7 sets minimum domestic hot water standards for permanent residences. A solar water heater on a permanent residence must meet OBC standards before passing inspection.
NEC and CEC code requirements
NEC Article 690 governs solar PV installations including any battery-connected solar water heater control board circuit. Pump circuits for solar thermal must be sized for rated current plus a 25% safety factor. A 120V AC circuit feeding a propane tankless control board needs proper protection under NEC 240. Current standards are published at nfpa.org.
CEC Section 64 governs solar PV installations in Ontario. A solar thermal pump powered by the off-grid system requires an ESA permit for the wiring. The TSSA Act governs propane appliances and requires a G2-licensed gas fitter for all gas connections. The Electrical Safety Authority provides current compliance guidelines at esasafe.com.
Pro Tip: Run the January production test on your SmartShunt before finalising any solar water heater. On a clear Ontario January day, note total array production by 9 AM. Two 8-minute electric on-demand showers consume 480Wh, leaving only 240Wh from a 720Wh January day. Propane passes the test every time at 1W ignition and 15W control board.
Solar water heater verdict: propane wins, solar thermal supplements
- Off-grid Ontario property owners below Tier 3: Specify propane on-demand from day one. A 40,000 BTU unit at $350 to $500 covers 1 to 2 person properties. A 150,000+ BTU whole-home unit at $800 to $1,500 covers 3 to 5 person residences. Both pass the SmartShunt test at 1 to 3W during use.
- Seasonal cottage owners with existing propane infrastructure: Add solar thermal as a Phase 2 upgrade. The Burlington Guelph Line result confirms 85% summer hot water from a $3,800 install. Winterize the glycol loop in October each year. Recommission the system in May with a fresh propylene glycol top-up.
- Off-grid owners running electric on-demand with morning battery depletion: Replace it with propane tankless this season. The Edinburgh Road 480Wh morning load disappeared from the SmartShunt graph the day after the swap. The bank stabilized at 80 to 95% SoC through every morning routine.
Frequently asked questions
Q: What is the best solar water heater for an off-grid property in Ontario?
A: Propane tankless is the correct year-round choice for any Ontario off-grid property below Tier 3. It delivers unlimited hot water at $0.15 to $0.30 per shower. Battery draw is 1 to 25W for the control board only. Solar thermal works as an excellent summer supplement at zero operating cost.
Q: Do I need glycol in my solar thermal system in Ontario?
A: Yes, unconditionally. Plain water in any outdoor solar thermal collector freezes on the first Ontario night below -5C. The vacuum tubes shatter or the flat plate channels burst. A 50% glycol mix protects the system to -35C, covering every Ontario winter temperature.
Q: What is the cost difference between propane and electric solar water heating off-grid?
A: Propane tankless costs $0.15 to $0.30 per shower in propane fuel. Annual cost for a family of 4 is $250 to $400. Electric on-demand at 1800W draws 240Wh per shower, gone in 8 minutes. Two showers depletes a 100Ah 12V LFP bank by 50% before 9 AM.
This build is engineered within the 48V DC Safety Ceiling. Diagnostic logic is based on 20+ years of technical service experience. All structural and electrical installations must be verified by a Licensed Professional and comply with your Local AHJ. See our legal and safety disclosure for full scope.
About the Author
Robert Bertrand spent 20 years as a service advisor in the automotive industry (Lexus and Nissan), where precision diagnostics, wiring integrity, and documentation standards were non-negotiable. He brings that same technical discipline to GridFree Guide, where he researches, tests, and documents off-grid solar systems for Ontario conditions. Based in Rockwood, Ontario, every article is built on verified specifications, manufacturer data, and the real-world climate constraints of Canadian off-grid living.
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