Choosing the wrong solar water heater for an Ontario off-grid property is the fastest way to drain a battery bank before breakfast, and the correct choice depends entirely on occupancy, season, and whether the property is seasonal or year-round. A homeowner on Edinburgh Road South in Guelph, Wellington County installed a 9kW electric tankless water heater when he commissioned his full off-grid residence in fall 2023. His battery bank was 200Ah LFP at 24V, approximately 3,840Wh of usable capacity. Two standard 8-minute showers at 1,800W, a realistic residential tankless specification, consumed approximately 480Wh from the battery bank every morning.
In January his 600W panel array produced approximately 720Wh on a clear day at 1.5 peak sun hours. Two morning showers consumed 480Wh before 9 AM, leaving approximately 240Wh of production remaining for the fridge, Starlink, lighting, and everything else through the rest of the day. On overcast January days his panels produced approximately 100 to 200Wh, the morning showers consumed that entire production budget before a single other load ran. His battery bank was depleted to below 20% SoC by mid-morning on consecutive overcast days, requiring generator supplementation on days he had planned to manage without it.
I reviewed the corrected system at the commissioning check in March 2024. He replaced the electric tankless with a propane tankless unit drawing approximately 1W for electronic ignition and approximately 15W for the control board during operation. His January Victron SmartShunt logs after the propane switch showed the battery bank stable at 80 to 95% SoC through the full morning routine including two showers, kitchen hot water, and dish washing.
The solar water heater question was settled: propane for year-round Ontario domestic hot water, with solar thermal as a summer supplement when the budget allows. The 480Wh morning load disappeared from the SmartShunt consumption graph the day after the propane switch. See our Ontario solar sizing guide before designing any domestic hot water system into a solar budget.
The solar water heater decision: propane, solar thermal, or electric on-demand
| System | Cost installed | Battery draw | Winter performance | Ontario verdict |
|---|---|---|---|---|
| Propane tankless | $800 to $1,500 | ~15 to 25W (control board) | Excellent (-42C) ✓ | Year-round standard ✓ |
| Solar thermal + glycol | $3,000 to $6,000 | ~50W (pump only) | Needs propane Nov-Apr | Summer supplement ✓ |
| Electric on-demand | $200 to $600 | 240Wh per shower | 480Wh = 50% of 100Ah ✗ | Tier 3 only ✗ |
Propane tankless delivers instant, unlimited hot water with approximately 15 to 25W of battery draw for the control board and ignition circuit. Ontario well water at 5 to 10C in January is handled instantly at any ambient temperature. Cost: $800 to $1,500 installed including the unit and a TSSA-licensed gas fitter. This solar water heater path has zero impact on the battery bank beyond the small control board draw and is the correct year-round Ontario specification for any property below Tier 3 capacity.
Solar thermal provides free domestic hot water from May through September at 80 to 100% coverage, requiring a closed-loop glycol system to prevent freeze damage to collectors on the first Ontario night below -5C. A propane backup is required from November through April when solar thermal output drops to minimal levels at 1.5 peak sun hours and low sun angle. Electric on-demand at 1,800W draws 240Wh per shower, 480Wh for two, on a 100Ah 12V bank that is 50% of usable capacity before 9 AM, and on a 200Ah 24V bank it consumed 67% of the Edinburgh Road South January production budget before other loads ran. See our off-grid shower guide for the full shower-specific energy comparison.
Propane tankless: the Ontario year-round domestic hot water standard
A propane tankless solar water heater equivalent delivers unlimited hot water at approximately $0.15 to $0.30 per shower, handles Ontario well water at 5 to 10C in January instantly, and draws no meaningful battery capacity for heating. A 6 L/min unit is adequate for 1 to 2 person properties with a single simultaneous draw. A 150,000+ BTU whole-home unit is required for 3 to 5 person properties where a shower and kitchen sink may run simultaneously. TSSA-licensed gas fitters are mandatory for all permanent propane connections in Ontario, adding $400 to $800 in installation labour to the unit cost of $400 to $700.
The battery ignition point is the detail that most installations miss. A propane tankless unit requires a reliable battery supply for the electronic ignition (~1W) and control board (~10 to 25W during operation). In an unheated Ontario utility room at -20C, a standard LFP battery without cold charging protection may refuse a charge on cold mornings, leaving the ignition circuit unable to fire and the household without hot water.
A Battle Born heated LFP battery in the utility room maintains charge acceptance to -20C ambient, ensuring the ignition circuit is always powered regardless of utility room temperature. For a 420 lb propane tank shared with the tankless water heater and a backup generator, two scheduled annual deliveries typically covers a 2-person year-round Ontario residence. 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. A flat plate or evacuated tube collector array with a 200 to 300L storage tank provides approximately 80 to 100% of domestic hot water requirements from May through September at zero operating cost. A cottage owner on Guelph Line in Burlington, Halton County added a solar thermal flat plate system to her seasonal cottage in spring 2023. Her installed cost was approximately $3,800. From Victoria Day through Thanksgiving the system provided approximately 85% of her domestic hot water requirements, saving approximately $180 to $190 per season in propane costs. She correctly winterized the glycol loop in late October each year, three seasons, no freeze damage.
The glycol mandatory rule: a closed-loop propylene glycol and water mixture must circulate through the collectors rather than plain water. Plain water in outdoor solar thermal collectors will freeze on the first Ontario night below -5C and shatter the vacuum tubes or burst the flat plate panel channels. A 50% glycol mix provides freeze protection to approximately -35C. Annual glycol concentration testing and top-up takes approximately 30 minutes and costs approximately $20 to $40.
For seasonal Ontario properties, drain the entire loop in October and recommission in May. For year-round properties, maintain the glycol concentration year-round without draining and confirm a propane backup is commissioned before November. See our solar battery bank sizing guide for how to include the solar thermal circulation pump load in the daily energy budget.
Pro Tip: Before finalising any solar water heater selection, run the January production test on your SmartShunt. On a clear Ontario January day, note the total array production by 9 AM. Then calculate the hot water energy budget: at 1,800W electric on-demand, two 8-minute showers consume 480Wh. At a January clear-day production of 720Wh (600W array), 480Wh for hot water leaves 240Wh for everything else. If the hot water budget exceeds 50% of January morning production, electric on-demand will create a chronic morning deficit on every overcast day throughout the winter. Run this calculation with your specific array size and January PSH before purchasing any electric solar water heater component. Propane passes the test every time: ~1W ignition, ~15W control board, zero Wh of battery storage consumed for the hot water itself.
Solar water heater sizing: matching output to Ontario household demand
Sizing the correct solar water heater for an Ontario household requires matching output to occupancy, season, and simultaneous draw requirements. For 1 to 2 person seasonal cottages: a 6 L/min propane tankless unit or a 100 to 150L solar thermal storage tank with a single collector panel provides adequate domestic hot water. For 3 to 5 person permanent residences: a 150,000+ BTU whole-home propane unit handles simultaneous shower and kitchen sink draws without temperature drop. Solar thermal for a 3 to 5 person household requires a 300 to 400L storage tank and approximately 4 to 6 square metres of collector area to provide 70 to 85% annual hot water coverage.
Ontario Building Code Section 7 requires permanent residences to meet minimum domestic hot water provision standards including minimum flow rates and temperature delivery. A solar water heater system for a permanent Ontario residence must meet these OBC standards before passing the building inspection. Confirm compliance requirements with the local building department before finalising any solar water heater specification for a permanent off-grid Ontario residence. Seasonal cottages not occupied year-round are typically exempt from permanent habitation standards but should be designed to meet the occupants’ practical daily hot water demand at peak summer occupancy.
NEC and CEC: Ontario requirements for off-grid hot water installations
NEC 690 governs solar PV installations. A solar water heater with a solar thermal collector connected to a circulation pump powered by the off-grid solar system must comply with NEC 690 DC wiring requirements for the pump circuit. The pump circuit must be sized for the pump’s rated current plus a 25% safety factor, with appropriate fusing at the battery terminal. A 120V AC circuit feeding the propane tankless control board must be on a properly protected branch circuit from the inverter output panel, complying with NEC 240 appliance circuit requirements. Contact the NFPA at nfpa.org for current NEC requirements for residential solar PV and hot water appliance circuit installations.
CEC Section 64 governs solar PV installations in Ontario. A solar thermal system with a circulation pump powered by the off-grid solar system requires an ESA permit for the electrical wiring connecting the pump to the battery bank or charge controller. The TSSA Act governs propane appliances in Ontario, a propane tankless solar water heater requires a TSSA-licensed gas fitter for all gas line connections, venting, and commissioning regardless of whether the property is off-grid or grid-connected. The Ontario Building Code governs domestic hot water provision for permanently occupied dwellings. Contact the Electrical Safety Authority Ontario at esasafe.com before wiring any solar water heater electrical components in an Ontario off-grid installation.
The solar water heater verdict: which system fits your Ontario property
- Ontario seasonal cottage owner occupied May through October with a propane supply already on site: add solar thermal as a Phase 2 supplement to the existing propane tankless. The Burlington Guelph Line result confirms the economics: $3,800 installed, $180 to $190 propane savings per season, break-even at approximately 20 seasons without accounting for propane price increases. For a cottage used 20 or more years, solar thermal is a sound investment. Start with the propane tankless as the primary solar water heater and add solar thermal when the budget allows. The glycol winterization takes approximately 30 minutes each October and protects the system at no additional operating cost.
- Ontario year-round off-grid residential owner needing full-time domestic hot water for 1 to 5 people: propane tankless is the correct specification. A whole-home 150,000+ BTU unit installed by a TSSA-licensed gas fitter at $800 to $1,500 total cost delivers unlimited instant hot water at approximately $0.15 to $0.30 per shower with zero battery bank draw beyond the 15 to 25W ignition and control board circuit. The Edinburgh Road South result is the cost of the alternative: electric on-demand leaves 240Wh for all other loads after two January showers on a 600W array, depleting the bank below 20% on consecutive overcast days.
- Ontario off-grid owner currently running electric on-demand hot water and experiencing chronic battery depletion by mid-morning: replace it with propane tankless immediately. Check the Victron SmartShunt logs for the hot water draw block, typically a sustained 1,800W load for 8 to 16 minutes every morning. The Edinburgh Road South result: 480Wh morning load gone the day of the propane switch, bank stable at 80 to 95% SoC through the full morning routine. If the battery enclosure is in an unheated space below 0C, add a Battle Born heated LFP to ensure the ignition circuit has a reliable power source in cold utility rooms.
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 capacity. It provides unlimited hot water at approximately $0.15 to $0.30 per shower with zero battery bank draw for the heating function itself. Solar thermal is an excellent summer supplement for seasonal properties, providing approximately 80 to 100% of domestic hot water requirements from May through September at zero operating cost. Electric on-demand solar water heater equivalents require a minimum 500Ah LFP bank at 24V and 2,000W or more of panels to avoid chronic morning battery depletion, the Edinburgh Road South Guelph result confirms the consequence of undersizing: below 20% SoC by mid-morning on consecutive overcast January days.
Q: Do I need glycol in my solar thermal system in Ontario?
A: Yes, unconditionally. Plain water in any outdoor solar thermal collector in Ontario will freeze on the first clear night below -5C and shatter the vacuum tubes or burst the flat plate panel channels. This is not a risk to manage, it is a certainty that will destroy the collector on the first Ontario fall night without glycol protection. A closed-loop propylene glycol and water mixture at 50% concentration provides freeze protection to approximately -35C, covering every Ontario winter ambient temperature. Test glycol concentration annually with a refractometer and top up to maintain protection. For seasonal properties, drain the entire solar water heater loop in October and recommission in May.
Q: How much does it cost to heat water with propane vs electricity off-grid?
A: Propane tankless costs approximately $0.15 to $0.30 per shower in propane fuel. Electric on-demand at 1,800W draws approximately 240Wh per shower, at Ontario off-grid solar electricity costs of approximately $0.20 to $0.40/kWh equivalent (based on battery cycle cost), a single electric shower costs approximately $0.05 to $0.10 in stored energy. The problem is not the direct cost per shower but the capacity constraint: 480Wh for two showers depletes a 100Ah 12V LFP bank by 50% before 9 AM, consuming 67% of a 600W array’s entire January clear-day production. Propane removes this constraint entirely and the solar water heater system runs at 15 to 25W for the control board rather than 1,800W for the heating element.
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.
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