Size a residential or commercial boiler from room-by-room heat loss. Applies industry-standard oversizing guidance and Canadian design temperatures for accurate capacity selection.
Size a boiler from building heat loss. Calculate required output BTU/hr or kW, account for distribution losses, and apply industry sizing rules. Covers gas, oil, and electric boilers.
Calculate boiler AFUE and seasonal efficiency from flue gas temperature and excess air measurements. Compare condensing vs. non-condensing boiler economics at your gas price.
Size steam boilers for one-pipe and two-pipe systems. Calculate EDR, connected load, and pick-up factor. Covers low-pressure steam common in older Canadian buildings.
Calculate output, flow rate, and delta T for hot water boilers at standard and low-temperature conditions. Compare operating costs at current Canadian natural gas rates.
Size cast iron and steel radiators from room heat load and supply water temperature. Corrects EDR ratings for non-standard operating conditions and calculates required number of sections.
Size hot water baseboard heaters from room heating load and supply water temperature. Calculate required baseboard length and verify against manufacturer output ratings.
Design radiant floor heating systems. Calculate tube spacing, supply water temperature, heat output per square metre, and zone flow rates for PEX tubing in slab or staple-up installations.
Calculate actual heat output for any emitter type at your system's supply temperature. Covers baseboard, panel radiators, fan coils, and radiant floors with temperature correction factors.
Size natural draft and fan-assisted flue systems per NBC and CSA B149.1. Calculate flue diameter, height, and available draft for gas-fired boilers in Canadian climate conditions.
Calculate boiler combustion efficiency from flue gas CO2, O2, and stack temperature readings. Identify combustion losses and find the optimal air-fuel ratio for gas or oil-fired boilers.
Calculate heating oil consumption, seasonal cost, and nozzle sizing for oil-fired boilers. Compare No. 2 fuel oil economics against natural gas and heat pumps at Canadian energy prices.
Calculate natural gas consumption (GJ/season) and operating cost for gas-fired boilers. Includes Canadian carbon pricing impact and compares to alternative heating fuels by province.
Calculate propane consumption, tank sizing, and seasonal heating cost for propane-fired boilers. Compare cost-per-GJ against natural gas, fuel oil, and heat pumps for rural Canadian properties.
Calculate cord wood or wood pellet consumption for wood-fired boilers. Size storage, estimate seasonal cost, and compare efficiency ratings for outdoor wood boilers common in rural Canada.
Calculate district heating connection loads, heat exchanger sizing, and substation requirements. Size pre-insulated buried piping for district systems in Canadian municipalities.
Plot the system resistance curve for a hydronic heating circuit. Find the pump operating point where the pump curve intersects the system curve for correct flow and head.
Calculate supply-to-return temperature differential for hydronic systems. Find the optimal delta T for condensing boiler efficiency, heat emitter output, and flow rate requirements.
Size primary and secondary loops for primary-secondary hydronic systems. Calculate closely-spaced tee sizing, primary flow, and zone pump requirements for multi-temperature systems.
Calculate condensing efficiency, latent heat recovery, and seasonal savings vs. a non-condensing boiler. Determines the minimum return water temperature required to achieve condensing mode.
Size and analyze modulating-condensing boilers. Calculate turndown ratio, minimum firing rate, part-load efficiency, and annual fuel savings compared to conventional boilers.
Design outdoor reset control curves for modulating boilers. Calculate supply water temperature at any outdoor temperature to maintain comfort and maximize condensing efficiency.
Size low-loss headers (hydraulic separators) for multiple boiler and zone pump installations. Calculate required velocity, pressure drop, and header diameter for hydraulic decoupling.
Design hydronic snowmelt systems for driveways, walkways, and loading docks. Calculate slab heat flux, tube spacing, glycol flow rate, and boiler load for Canadian winter conditions.
Size biomass boilers for wood pellet, wood chip, or agricultural residue fuels. Calculate fuel consumption, storage volume, and emissions compliance considerations for Canadian biomass heating projects.
About Boiler & Hydronic Heating Calculations
Hydronic heating systems circulate hot water or steam through pipes to radiators, baseboard, radiant floor tubing, or fan coils, delivering comfortable, even heat throughout a building. Getting a hydronic system right requires coordinating the boiler, the piping, the pump, and the heat emitters as one integrated system — each component's sizing depends on the others.
Sizing the Boiler
Every hydronic system starts with a correctly sized heat source. The boiler sizing calculator and boiler output calculator convert your building's heat loss into the required boiler capacity, accounting for distribution losses and oversizing allowances. For fuel-specific consumption and cost estimates, use the natural gas calculator, propane calculator, fuel oil calculator, wood boiler calculator, or biomass boiler calculator depending on your fuel source. Older buildings with steam systems should use the steam boiler calculator to work in EDR and pick-up factor rather than the hot water flow-based methods used elsewhere.
Maximizing Condensing Efficiency
Modern condensing boilers only achieve their high rated efficiency when return water drops below about 55°C. The condensing boiler calculator quantifies this relationship and estimates seasonal savings, while the outdoor reset calculator designs the control curve that keeps supply and return temperature appropriately low across the heating season. Pair this with the mod-con boiler calculator to confirm the boiler's turndown ratio matches your building's actual load profile, avoiding short-cycling on mild days. Use the combustion efficiency calculator and boiler efficiency calculator for field verification of AFUE from flue gas readings.
Choosing and Sizing Heat Emitters
The heat emitter you choose determines what supply temperature your system needs, which directly affects boiler efficiency. Compare all emitter types side by side with the heat emitter calculator, then size the specific emitter with the baseboard heating calculator, radiator sizing calculator, or radiant floor heat calculator. For heated driveways and walkways, the snowmelt calculator handles the much higher heat flux requirements of outdoor slab heating.
Piping, Pumps, and Multi-Zone Systems
Correct flow rate and pipe sizing starts with the delta-T heating calculator, which shows how your choice of supply-return temperature split affects flow and pipe size. The system curve calculator finds the actual pump operating point for correct circulator selection. Multi-zone systems need hydraulic separation — use the primary-secondary piping calculator for closely-spaced tee systems or the low-loss header calculator for header-based separation on larger systems. Large campus or community systems should start with the district heating calculator for building connection sizing.
Related Tools You May Need
- Before sizing a boiler, confirm your building's heat loss with the heat load calculator and design temperature lookup.
- For the piping itself, use the pipe sizing calculator in our Piping & Plumbing category.
- Compare efficiency upgrades with the payback period calculator and SEER calculator for the cooling side.
- Convert results between units with the BTU to kWh converter or temperature converter.
- Check ventilation compliance with the ASHRAE 62.1 ventilation calculator.
Frequently Asked Questions
Start with a room-by-room heat loss calculation at your local design outdoor temperature, from -4°C in Vancouver up to -33°C in Winnipeg. The total heat loss is your baseline. Divide by your distribution efficiency (0.85–0.90 for most homes) to get the boiler output needed at the emitters, then add 15–25% for oversizing to handle morning pick-up and occasional domestic hot water demand. Use the boiler sizing calculator for a complete, step-by-step result.
A condensing boiler needs return water below approximately 55°C to recover latent heat from flue gas and achieve its rated high efficiency. Above this threshold it performs closer to a standard 80–85% efficient boiler despite its higher purchase price. The outdoor reset calculator designs a control curve that keeps supply and return temperature appropriately low across the heating season, and the condensing boiler calculator quantifies the resulting efficiency and savings.
Radiant floor heating performs best at low supply temperatures thanks to its large surface area, often delivering full output at 35–45°C. Fan coils come next due to forced convection, followed by panel radiators, and finally fin-tube baseboard, which typically needs 70°C or higher unless substantially oversized. Use the heat emitter calculator to compare all four emitter types side by side at your specific supply temperature and room load.
Both achieve hydraulic separation between a boiler's primary loop and one or more secondary zone loops, but differently. Primary-secondary piping uses closely-spaced tee pairs directly on the primary pipe for each zone connection. A low-loss header uses a larger vessel that the boiler feeds into and zones draw from, using low internal velocity for separation instead of tee spacing. Low-loss headers are often preferred for systems with many zones or multiple boilers. See the primary-secondary piping calculator and low-loss header calculator to compare both approaches for your project.
Yes — all AskHVAC.ca tools are fully responsive and work on any smartphone or tablet without an app install. They run entirely in your browser, switch between Imperial and Metric with a single tap, and results can be exported to PDF or CSV directly from your phone. Use them freely at the job site, in the truck, or in the office.