Propane and CO₂ in Ontario greenhouses — a working-grower reference

If you operate a greenhouse in Southwestern Ontario outside the Enbridge natural-gas distribution footprint — most of Norfolk, Brant, Haldimand, and the rural concessions of Oxford, Perth, and Wellington — propane is doing two jobs at once. It is heating the range through winter, and it is the CO₂ source feeding the crop during the day. Both jobs come off the same tank manifold, and the spec of the fuel matters to both.

This article is the working-grower reference: what the HD-5 specification buys you, where ethylene and propylene damage shows up and at what levels, the equipment categories, tank sizing and setbacks, the regulatory frame, the seasonal demand curve, and the supply-continuity question every honest propane conversation eventually reaches. Everything below is grounded in OMAFRA Publication 370 and Factsheet 290/27, CAN/CGSB-3.14, CSA B149.2-20, Ontario Regulation 211/01, the federal Environmental Emergencies Regulations (SOR/2019-51), and the public record around the November 2019 CN Rail strike.

What propane is doing in a greenhouse

Two jobs, one fuel.

Heat. Norfolk, Brant, and Oxford sit in the 3,900–4,050 annual heating-degree-day range (Environment Canada Climate Normals 1981–2010 and 1991–2020). Lake Erie moderation makes the Norfolk corridor among the milder Ontario zones, but November through February still takes 65 to 70 percent of a year-round ornamental range’s annual fuel, with peak weekly draw landing mid-January. Bedding-plant ranges run a flipped curve: minimal winter idle, ramp in February, March through early May the crunch.

CO₂. Each litre of propane combusted yields roughly 1.8 kg of CO₂ (OMAFRA Factsheet 290/27). With ambient at about 420 ppm in 2026, supplementation to 800–1,000 ppm during the day with vents closed is the OMAFRA recommendation; the saturation point on most crops sits around 1,000–1,300 ppm under ideal conditions. Vegetable operations push the upper end of that band; seedlings, lettuce, and most floriculture sit at the lower end.

The structural fact underneath both jobs: the Enbridge natural-gas distribution main does not reach much of the rural concession-road footprint where Ontario’s propane-served greenhouses operate. The Leamington-Kingsville vegetable cluster runs on natural gas. The Norfolk–Wellington–Perth ornamental, bedding-plant, propagation, and nursery base does not, and is not getting it. Propane is the fuel because it is the fuel available, and the program is built around that reality.

The HD-5 spec, and why purity is operational

HD-5 is the Canadian propane specification used for residential, agricultural, and commercial combustion. The standard is CAN/CGSB-3.14, aligned with U.S. GPA HD-5. The two thresholds that matter inside a greenhouse:

• Minimum 90% propane content by liquid volume.
• Maximum 5% propylene.

In a furnace those numbers are an efficiency note. Inside a greenhouse they are an agronomic threshold. OMAFRA names the failure modes: premature senescence on tomato and cucumber, flower shatter in geraniums, flower bud abortion in chrysanthemums and poinsettia. The damage threshold for ethylene in the canopy is 0.05 ppm. Ethylene comes from incomplete combustion; propylene is specifically associated with propane. Leaky supply lines have caused serious financial damage to Ontario growers.

Two operational consequences:

1. Flue-gas CO above 50 ppm is the canopy-damage signal for ethylene. A CO meter on the flue at the next combustion tuning is the cheapest piece of agronomic insurance in the program.
2. Sulphur shouldn’t exceed 0.02% by weight, and the burner has to be low-NOx if its flue gas goes into the canopy. OMAFRA: “Boilers equipped with low NOx burners must be used for flue gas utilisation as a CO₂ source.”

The practical rule: annual combustion tuning on every boiler and CO₂ generator, with a flue-gas CO check on the same visit. A range that ran clean last year does not necessarily run clean this year.

Equipment categories

Three heater categories cover the propane-served greenhouse installed base in Ontario, plus dedicated CO₂ generators where flue-gas-into-canopy isn’t the right architecture.

• Hot-water boilers dominate larger floriculture. Pairing with a thermal storage tank lets daytime CO₂ get pulled off the flue gas through a condenser.
• Direct-fired unit heaters are common in smaller ranges and bedding-plant operations. Vented units keep combustion gases out of the canopy; unvented units still exist in some bedding-plant ranges and carry the most ethylene and CO risk on the OMAFRA thresholds.
• Infrared tube heaters appear in propagation tunnels where spot heat is wanted.

Dedicated propane CO₂ generators sit alongside the heat plant in most Norfolk-style operations — Reznor, Roberts Gordon, Priva, and Johnson Gas Appliance are the common OEMs. Units typically run 20,000–60,000 BTU/hr and cover about 4,800 sq. ft. each. Most operators target the 800–1,000 ppm daytime band OMAFRA recommends for seedlings, lettuce, and most floriculture. CO₂ enrichment adds roughly 10–15% to fuel consumption depending on venting strategy.

Tank sizing, manifolded storage, and vaporizers

Sizing is driven by burner load and the minimum-inventory-floor logic for winter draw — not by greenhouse acreage alone. The common configurations across the propane-served Ontario greenhouse base:

Vaporizers convert liquid propane to vapour at a rate the burners can pull when tank-surface vapourization can’t keep up. Sustained draw above about 1.5 M BTU/hr per 30,000 USWG tank at −10 °C calls for a vaporizer or additional capacity. Most 2-acre-or-smaller year-round ornamental loads stay under that with a manifolded 2× 30,000 USWG set; propane-fired vegetable operations almost always need an external vaporizer.

Manifolding matters for more than capacity. Running all tanks down evenly through the season — rather than running one to empty before opening the next — leaves you covered if a single tank fails inspection mid-winter.

CSA B149.2-20 Table 5.2, adopted in Ontario through O. Reg. 211/01, governs placement. For a 30,000 USWG tank, the minimum setback is 50 ft (15 m) from buildings, property lines, and ignition sources. Smaller bulk tanks (1,000–4,000 USWG) sit in the 10–25 ft range. PRV discharge, transfer-pump placement, hose connection, and fencing live in Section 6 of B149.2.

The regulatory frame

Four documents govern a greenhouse propane installation in Ontario.

• O. Reg. 211/01 — Propane Storage and Handling. Distributors cannot legally supply propane to an installation that hasn’t been inspected within the previous ten years (s. 18). On any acquired property, the most recent §18 inspection report is the most important piece of paperwork in the file.
• TSSA Director’s Order FS-271-24. Propane tanks with a Maximum Allowable Working Pressure below 250 psig had to be out of service by October 1, 2025. Tanks installed before approximately 2010 should have had their MAWP checked against the nameplate. Distributors cannot fill non-compliant equipment.
• Federal Environmental Emergencies Regulations, 2019 (SOR/2019-51) — the E2 plan. On-site propane storage at or above 4.5 tonnes (about 9,300 L liquid) triggers a federal E2 obligation. A single 4,000 USWG tank sits right at the threshold; most multi-tank greenhouse installations are well past it. This is the most common compliance gap on a manifolded greenhouse installation — operators track O. Reg. 211/01 because the distributor’s inspections enforce it, and miss the federal obligation because no visit triggers it.
• TSSA Risk and Safety Management Plan (RSMP). RSMP review typically becomes a serious question above roughly 5,000 USWG (about 19,000 L) on-site, though the determination is by activity, not by volume. A manifolded 2× 30,000 USWG configuration should expect TSSA review of private-outlet status. Confirm in writing with TSSA Fuels Safety at design time.

Seasonal demand and pre-positioning

A year-round Norfolk ornamental operation burns roughly 125,000–185,000 L per acre per year under a double-poly envelope. A 2-acre poinsettia / spring-mum range works out to 250,000–370,000 L/year, with January peak weeks at 15,000–25,000 L. CO₂ enrichment adds another 10–15%.

Bedding-plant ranges flip the curve: 12–14 weeks of consumption concentrated Feb–early June. A 4-acre Wellington or Perth operation typically runs 160,000–320,000 L over the February–April peak, with weekly draw of 20,000–30,000 L through the March crunch.

The rules that fall out of those curves:

• Year-round ornamental: top off above 85% by November 1. Tanks fill to 80–85% for thermal expansion; 100% fill is unsafe.
• Bedding-plant: top off in January, not November. The February ramp moves faster than the supplier’s truck cadence can backfill an empty tank.
• Maintain a 21-day winter inventory floor at peak draw. For a 2-acre Norfolk ornamental at 20,000 L/week peak that’s roughly 60,000 L on hand at all times — comfortably inside a manifolded 2× 30,000 USWG configuration.
• Confirm a written winter delivery schedule with your primary supplier by October 1. A verbal arrangement is not a schedule.

Supply continuity — the structural risk

This is the part of the propane conversation that doesn’t have a happy ending, and an honest article has to name it plainly.

Where the molecule comes from. Almost all Eastern Canadian propane fractionates out of the Plains Midstream Canada Sarnia NGL fractionator. Sixty-three percent of Canadian propane moves by rail; Quebec is 83–85% rail-supplied from Sarnia. Southwestern Ontario sits inside truck-deliverable range of the terminal — the geometric reason a distributor with tanker pickup at Sarnia can keep moving volume when rail can’t.

The November 2019 reference event. The 8-day CN Rail strike of November 19–26, 2019 produced the most severe Eastern Canadian propane disruption in recent record. Three days in, Quebec was at 20% of normal reserves and the Premier had declared an emergency. Tank truck lineups at the Sarnia terminal stretched for hours. Keith Currie, then OFA President, to Global News: “Many of our customers have already been notified by their propane suppliers that they’re going to be cut off.”

The CPA allocation hierarchy. When supply tightens, the Canadian Propane Association allocates against an informal tiered hierarchy — not statutory, industry practice that emerged from 2019, but the operative reference:

• Tier 1. Hospitals, water treatment, public infrastructure and emergency services, residential heat.
• Tier 2. Livestock barn heat, where animal welfare is at stake.
• Tier 3. General agriculture — including greenhouse heating where no livestock is on-site — and general commercial.

Nathalie St-Pierre, then CPA President, to RealAgriculture in November 2019: “agriculture would fall into a lower level tier, unless the propane is needed to heat a barn with livestock in it.”

A greenhouse without livestock is in Tier 3. That is a fact of the regulatory landscape, not a slight. It is also the reason the structural hedges — manifolded storage above bare-minimum sizing, pre-positioning above 85% by November 1, a 21-day winter floor, a written delivery schedule confirmed by October 1 — matter more in this segment than in almost any other propane account. None of those eliminate the tail risk of a multi-week rail interruption. What they do is widen the window between disruption starting and your range running out of fuel, on a basis that does not require anyone’s charity.

A short FAQ

Is propane actually a clean CO₂ source?

Yes, provided three conditions hold: the supply is HD-5, supply lines and burners are leak-tight and properly tuned, and the burner is low-NOx if its flue gas is going into the canopy. The OMAFRA contamination thresholds — 0.05 ppm ethylene at the canopy, 50 ppm CO at the flue as the indicator — are the operating envelope. Annual combustion tuning with a flue-gas CO check keeps you inside it.

Does my installation need an E2 plan?

If on-site propane storage is 4.5 tonnes or more — about 9,300 L liquid, which a single 4,000 USWG tank reaches — yes. The Environmental Emergencies Regulations, 2019 require federal registration with ECCC and a documented response plan. The E2 obligation is independent of TSSA; satisfying one does not satisfy the other. On a manifolded 2× 30,000 USWG configuration you are well past the threshold.

What happens to my range if there’s another rail event like 2019?

A greenhouse without livestock is in Tier 3 of the CPA allocation hierarchy. No honest supplier guarantees delivery against a CN-strike-class disruption. What the program does is widen the buffer: manifolded storage well above bare-minimum sizing, pre-positioning above 85% by November 1, a 21-day winter inventory floor at peak draw, and a written delivery schedule confirmed by October 1. The conversation worth keeping is the one that names this risk honestly rather than the one that promises it away.

A note on what this article does not say

A single delivered-price figure for greenhouse propane is not in the article. Agricultural bulk in Southwestern Ontario sits in a $0.65–$0.95/L range as of May 2026, with the Sarnia wholesale hub running $0.45–$0.65/L over the same window. A point estimate would be misleading on a market that moves with the season and the contract structure. The article will be updated when verified primary sources support a tighter figure.