Case Study: One Old Mill Toronto — 278-Unit Condo Runs 30 Enerworks Solar Thermal Collectors
One Old Mill is a 278-unit high-rise condominium in Toronto's Etobicoke Old Mill neighbourhood. Its centralized domestic hot-water system uses 30 Enerworks solar thermal collectors on the building roof to displace natural-gas boiler load. The installation is one of the highest-profile Canadian multi-unit residential building (MURB) thermal solar retrofits — documented in Enerworks' case-study library and Toronto MURB energy-retrofit trade coverage. For condominium corporations and property managers evaluating solar for a large residential building, One Old Mill is the reference project. Here's the setup, why MURB scale changes the math, and what a comparable retrofit costs today.
The installation at a glance
| Parameter | Value |
|---|---|
| Location | Etobicoke, Toronto (Old Mill neighbourhood) |
| Building type | 278-unit high-rise condominium |
| Solar collectors installed | 30 Enerworks flat-plate or heat-pipe collectors |
| Manufacturer | Enerworks (Ontario) |
| Primary use | Centralized domestic hot water (DHW) for residents |
| Backup fuel displaced | Natural gas (central boiler) |
| Estimated annual solar fraction | 20-35% of annual DHW load |
| Documented as | Documented in Enerworks case-study library + Toronto MURB retrofit coverage |
A 278-unit MURB running centralized hot water is a very large thermal load — roughly 8,000-12,000 L/day of hot water depending on unit mix and occupancy patterns. 30 collectors on the roof deliver a meaningful share of that load, but not the whole thing. MURB solar thermal is a supplement to gas boiler operation, not a replacement.
Why MURB centralized hot water is a strong retrofit target
For a condo corporation or property management company operating a centralized DHW plant, several factors combine to make thermal solar retrofits attractive:
- The load is LARGE and STEADY year-round. Residents shower every day, in every season, regardless of weather. Unlike a school or a summer camp, MURB DHW never turns off.
- The building already has flat roof area. Unlike single-family homes where roof orientation and pitch are constrained, MURB roofs are typically flat with excellent solar access. Perfect for a tilted collector array.
- The DHW plant is centrally metered. Gas bills are visible and controllable — condo corp finance teams can measure savings against a baseline consumption.
- The federal Clean Technology ITC applies when the condo corp is properly structured. Nonprofit condo corp treatment differs from for-profit ownership — consult a tax advisor on the specific ownership structure for the DHW plant.
- Toronto Green Standard alignment. A completed thermal solar retrofit demonstrably lowers building GHG intensity — one of the metrics that will increasingly matter for MURB refinancing and resale valuation as green building standards mature.
What a comparable retrofit costs today
For a 200-350 unit MURB installing 25-40 collectors in 2026, expect the following approximate cost stack:
| Item | Cost range |
|---|---|
| 30 collectors + mounting | $100,000 - $170,000 |
| Insulated storage tank (4,000-6,000 L) | $25,000 - $45,000 |
| Glycol loop + heat exchanger + integration with existing boiler plant | $40,000 - $75,000 |
| Installation labour + plumbing + electrical | $45,000 - $90,000 |
| Roof access + structural review + membrane penetrations | $15,000 - $40,000 |
| Building integration engineering (retrofit into occupied building) | $10,000 - $30,000 |
| Total installed cost | $235,000 - $450,000 |
| Federal 30% Clean Tech ITC (if eligible structure) | -$65,000 - -$121,000 |
| Net cost after federal ITC | $170,000 - $329,000 |
| Expected payback (natural gas displacement) | 10-16 years typical for MURB |
MURB payback runs longer than dairy or hotel scale because of the lower solar fraction (residential demand curve mismatch) and the higher retrofit soft costs (occupied building, common-area work approvals, engineering scope for building systems integration). Even so, the combination of long asset life (25+ years), low ongoing maintenance, and TGS alignment makes it a strategic capital investment for many MURB corporations.
Lessons from the One Old Mill install
- MURB solar thermal is a real category — 200+ unit condos with centralized DHW are strong retrofit candidates despite longer payback than commercial hospitality installations.
- Toronto Green Standard alignment adds strategic value beyond straight payback. Buildings that measurably improve TGS-relevant metrics will retain resale value better as green building standards mature.
- Engage the condominium board early. MURB retrofits require unit-owner communication + board approval + reserve fund allocation. Building the case takes 6-12 months before construction starts.
- Solar thermal doesn't replace your boiler — it supplements it. Your existing gas plant remains the primary backup and must be maintained.
- Toronto HELP + federal ITC + IESO Save on Energy retrofit are three funding paths that can stack — verify current program terms and applicability at the corporation-ownership level before pricing.
Frequently Asked Questions
Can our smaller condominium (50-100 units) do the same thing?
Scaled-down versions work but with tighter economics. A 60-unit MURB with centralized DHW at 2,500-4,000 L/day demand can install 12-18 collectors for $110,000-$200,000, with payback typically 12-18 years for natural-gas displacement. For buildings without centralized DHW (each unit has its own tank), retrofit is much harder — solar thermal doesn't cost-effectively serve individual unit tanks in a MURB.
How do condo corporations handle capital financing?
Reserve fund allocations, special assessments, and Toronto's Home Energy Loan Program (HELP) all fund MURB retrofits. HELP is a City of Toronto financing program tied to the property tax bill — it removes the requirement for individual condo corporations to secure separate financing. Check current HELP terms + eligibility with the City of Toronto before pricing.
Does the federal Clean Tech ITC apply to a condominium corporation?
Depends on ownership structure. Standard condo corporations in Canada are typically nonprofit, which means the ITC (designed for taxable corporations) may not apply directly. Some MURB DHW retrofits are structured as a separate for-profit entity that leases equipment to the corporation — that structure can capture the ITC and pass through savings via lower operating fees. Consult a tax advisor familiar with condo corp structures + Clean Tech ITC.
How much do residents' hot water bills change?
In a centrally-metered MURB, residents don't pay individually for hot water — the corporation pays the gas + electricity bill and passes the cost through condo fees. When solar thermal reduces the corporation's gas bill by 20-35%, that savings flows through to reduced condo-fee pressure. Residents don't see a line-item change; they see a smaller fee increase over time.
Does solar thermal require any changes inside individual units?
No, when the retrofit is on a centralized DHW system. Everything happens in the mechanical room and on the roof — resident units are unchanged. Building-scale plumbing changes may require brief service interruptions during commissioning; a good installer schedules those to minimize disruption.
Is the One Old Mill system still operating?
The system has been documented as operational in Enerworks' case-study library and Toronto MURB retrofit trade coverage. We haven't independently verified current 2026 operational status. For a live reference call or an operational tour, contact Enerworks directly.
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