| Location / Room | Radiator Type | Sections | EDR/Section | Row EDR | |
|---|---|---|---|---|---|
| Total Connected EDR | 0 | ||||
🔎 EDR Reference Values by Radiator Type
Full Sizing Breakdown
| Parameter | Value | Notes |
|---|
How to Use the Steam Boiler Calculator
One-pipe steam systems use a single pipe that carries steam to the radiator and returns condensate back to the boiler. They're the most common type in older Canadian homes and apartments built before the 1950s. Two-pipe systems use separate supply and return mains and are more common in larger buildings. Vapour systems are a refined version of two-pipe, operating near atmospheric pressure. The type sets the pick-up factor used in the calculation.
If you can walk the building and count radiator sections, use the radiator entry table. Look up the EDR per section for the radiator type from the reference below the table. If you already have a total EDR figure from previous work, enter it directly. If you're starting from a heat loss calculation instead of a radiator survey, enter the heat loss in kW or BTU/h and the calculator converts it to EDR.
For the radiator table, add one row per room or radiator group. Select the radiator type, enter the number of sections, and the EDR per section auto-fills from the reference values. You can override the EDR/section field if you have manufacturer data for a specific model. The running total at the bottom of the table updates as you type.
Steam pipes radiate heat too. A 15% piping allowance is standard for one-pipe systems; 15–20% for two-pipe. This gets added to the connected EDR before applying the pick-up factor. Operating pressure affects steam temperature - residential systems typically run 0.5–2 psi. Most cast iron radiators are rated at their standard conditions, so pressure correction is minor at low residential pressures.
The results show connected EDR, EDR with piping allowance, EDR with pick-up factor applied, and the required boiler output in both BTU/h and kW. Select a boiler whose rated EDR output meets or just exceeds the required figure. Don't oversize steam boilers - an oversized unit cycles on pressure instead of thermostat demand, wasting fuel and causing water hammer.
Steam Boiler Sizing for Canadian Buildings
Steam heat is rare in new construction, but it's still running in tens of thousands of older Canadian homes and apartment buildings - especially in Montreal, Toronto, and Winnipeg, where pre-war housing stock is common. Getting a steam boiler replacement right requires understanding EDR, pick-up factor, and the peculiarities of steam distribution that don't apply to hot water systems.
What EDR Means and Why It Matters
EDR, Equivalent Direct Radiation, is the standard unit for measuring steam radiator output. One EDR equals 240 BTU/h at standard conditions: 215°F (102°C) steam temperature and 70°F (21°C) room air temperature. These conditions correspond to roughly 1 psi steam pressure. Every cast iron radiator sold in North America has been rated in EDR sections, and those ratings go back over a century with consistent methodology. To size a steam boiler, you simply add up the EDR of every radiator connected to the system.
One-Pipe vs. Two-Pipe Steam
In a one-pipe system, steam travels out through the supply pipe and condensate drains back through the same pipe by gravity, counter to the steam flow. Air vents on each radiator allow air to escape as steam fills the system. Two-pipe systems separate the steam supply from the condensate return, allowing for better control and quieter operation. Vapour systems - common in some older Canadian commercial buildings - operate at very low pressures near atmospheric, allowing very fine thermostat control. The pick-up factor differs between types because two-pipe and vapour systems have more separate piping to pre-heat.
The Pick-Up Factor
When a steam system starts cold - after a night setback or a power outage - the boiler must first heat all the metal in the pipes and radiators before useful heat reaches the rooms. This startup demand is called the pick-up load. The Hydronics Institute sets the standard pick-up factor at 1.333 for one-pipe systems and 1.25 for two-pipe. These factors are added to the connected EDR load plus piping allowance to determine the boiler's required output. A boiler selected without the pick-up factor may satisfy the steady-state load but fail to warm the building after a cold start - a real problem during a Prairie cold snap in Calgary or Winnipeg.
Piping EDR Allowance
Steam mains and branch pipes radiate heat into the basement or mechanical space. In a one-pipe system, this uninsulated pipe radiation is a free heat contribution in conditioned basements but an uncontrolled load in unconditioned crawl spaces. The standard piping allowance of 10–15% of connected radiator EDR accounts for this. For older buildings with long exposed mains in cold basements, use the higher end of the range. For buildings with insulated mains, you can reduce the allowance.
Don't Oversize a Steam Boiler
Oversizing is particularly harmful in steam systems. A boiler too large for its connected EDR builds pressure faster than the system can absorb it. The pressuretrol shuts the boiler off on pressure rather than the thermostat shutting it off on temperature, causing short cycling, water hammer from steam and condensate colliding in pipes, and poor heat distribution to remote radiators. The best replacement boiler matches the connected EDR as closely as possible - within 15% is ideal. Use the boiler sizing calculator for hot water replacement sizing if you're converting from steam to a hot water hydronic system.
Converting Steam EDR to kW
If you need to compare a steam boiler to a hot water boiler or a heat pump, convert EDR to kW using: 1 EDR = 240 BTU/h = 0.0703 kW. A building with 800 EDR connected load needs 800 × 240 = 192,000 BTU/h = 56.2 kW of boiler output before applying the pick-up factor. After the 1.333 pick-up factor for one-pipe, that becomes 256,000 BTU/h or 75 kW. That's the number to use when selecting the replacement boiler from a manufacturer's catalogue.
Frequently Asked Questions
EDR stands for Equivalent Direct Radiation. One EDR equals 240 BTU/h of heat output at standard steam conditions. To size a steam boiler, add up the EDR of every radiator in the building to get the connected load. Add a piping allowance of 10–15%, then apply the pick-up factor - 1.333 for one-pipe or 1.25 for two-pipe. The result is the required boiler EDR. Most Canadian boiler manufacturers publish EDR ratings alongside kW and BTU/h, making selection straightforward.
The pick-up factor accounts for the extra steam needed on a cold start to heat the piping metal and radiators before useful heat reaches the rooms. For one-pipe steam the standard factor is 1.333 (33% extra); for two-pipe it's 1.25 (25% extra). These values come from Hydronics Institute standards. Without the pick-up factor, a boiler that matches the steady-state connected load may fail to bring the building up to temperature after a setback - a serious problem during Canadian cold spells. Always apply the pick-up factor when selecting a replacement boiler.