HVAC Ductulator — Professional Duct Sizing Calculator for Ontario Homes
Free Online Duct Calculator — Size Round & Rectangular Ducts
Calculate optimal duct sizes for residential and commercial HVAC systems using industry-standard formulas. Includes CFM calculator, system designer, and material cost estimator.
💨 System Parameters
📐 Cross-Section View
✅ Results
Size Options
| Duct Size | Velocity | Noise Level |
|---|
📏 What CFM Do I Need? — Room-by-Room Calculator
Calculate required airflow (CFM) for heating and cooling based on room dimensions, insulation level, and your climate zone. Use this to determine total system CFM before sizing ducts.
Room Requirements
Use this value in the duct sizing calculator above to determine the correct duct size for this room.
🏠 Full System Designer — Multi-Room Duct Layout
Design an entire duct system with trunk line and multiple branches. Add rooms one by one, then generate a complete duct sizing schedule with material requirements.
Add Rooms to System
System Summary
Complete Duct Schedule
| Location | CFM | Duct Size | Velocity | Run Length |
|---|
💰 Material Cost Estimator
Calculate sheet metal requirements, weight, and estimated material costs for your duct system. Includes labor multiplier for installed pricing.
Material Requirements
Cost Breakdown
| Item | Quantity | Unit Cost | Total |
|---|
📚 HVAC Duct Sizing Guide — Everything You Need to Know
Comprehensive guide to duct sizing, airflow, and system design. Whether you’re a homeowner planning a renovation or an HVAC professional, this guide covers the fundamentals.
Understanding Airflow & CFM
CFM (Cubic Feet per Minute) measures how much air your HVAC system moves. A properly sized system typically requires 400 CFM per ton of cooling capacity. For example, a 3-ton AC needs approximately 1,200 CFM total. This airflow must be distributed across all rooms based on their heating and cooling loads. For accurate load calculations, use our Heat Loss Calculator for Ontario homes to determine precise BTU requirements.
Duct Sizing Methods Explained
Equal Friction Method (Most Common)
This method sizes ducts to maintain a constant friction loss per unit length (typically 0.08-0.10 inches of water column per 100 feet). It’s the standard for residential systems because it balances efficiency, noise, and cost.
- 0.08 in.w.c./100ft: Quiet, efficient, larger ducts — best for high-end homes
- 0.10 in.w.c./100ft: Standard residential — good balance of size and performance
- 0.15 in.w.c./100ft: Compact ducts, higher noise — used when space is tight
Velocity Method
Instead of targeting friction loss, this method sizes ducts to achieve a specific air velocity (FPM). It’s ideal for noise-sensitive applications or when you need precise velocity control.
- Supply ducts: 700-900 FPM (quiet operation)
- Return ducts: 500-700 FPM (lower noise)
- Main trunks: 900-1,200 FPM (acceptable for short runs)
Round vs. Rectangular Ducts
| Factor | Round Duct | Rectangular Duct |
|---|---|---|
| Efficiency | Best — 20-30% less friction loss | Good, but higher friction |
| Installation | Faster, fewer seams | More labor-intensive |
| Space Requirements | Requires more vertical clearance | Fits in tight spaces (floor joists) |
| Cost | Lower material + labor cost | Higher overall cost |
| Noise | Quieter — smooth airflow | Slightly louder |
| Best Use | New construction, open ceiling cavities | Renovations, limited vertical space |
Common Mistakes to Avoid
- Not accounting for duct run length: Long runs need larger ducts to overcome friction losses
- Ignoring flex duct penalties: Flex duct has 2-3× more friction than hard pipe — size accordingly
- Oversized return ducts: Return ducts should be larger than supply to maintain proper static pressure
- Too many bends: Each 90° elbow adds equivalent friction of 10-15 ft of straight duct
- Forgetting about fittings: Boots, reducers, and dampers add significant resistance