Furnace Replacement cost in London — overview
London, Ontario homeowners typically invest $3,500 to $9,500 for a complete furnace replacement, with most paying around $5,500 for a mid-efficiency natural gas unit. As southwestern Ontario's regional hub, London benefits from competitive pricing among multiple HVAC contractors serving the Forest City and surrounding townships. The city's moderate climate zone still demands reliable heating through winter months averaging -6°C, making furnace efficiency crucial for managing Enbridge gas bills. London's established residential neighbourhoods often require ductwork modifications when upgrading from older oil or electric systems to modern natural gas furnaces. Local contractors typically book 2-3 weeks out during peak season (September through November), though emergency replacements can often be accommodated within 48 hours. The Technical Standards and Safety Authority (TSSA) requires permits for all gas appliance installations in Ontario, adding regulatory oversight that protects homeowners but extends project timelines by 3-5 business days for inspection scheduling.
Where the money goes
| Component | Low estimate | High estimate | % of total | Notes |
|---|---|---|---|---|
| Standard Efficiency Furnace (80-85 AFUE) | $1,800 | $3,200 | 34% | Basic natural gas unit suitable for London's climate |
| High Efficiency Furnace (90-96 AFUE) | $2,500 | $5,500 | 58% | Condensing unit with improved efficiency ratings |
| Installation Labour | $800 | $1,800 | 19% | Licensed gas technician and helper, 6-12 hours |
| Venting and Gas Line Work | $300 | $1,200 | 13% | PVC venting for high-efficiency units, gas line modifications |
| Permits and Inspections | $150 | $300 | 3% | TSSA permit and mandatory gas connection inspection |
| Old Unit Removal | $100 | $250 | 3% | Disconnection and disposal of existing furnace |
| Total estimate | $5,650 | $12,250 | Pre-tax. Excludes permit fees unless noted. |
Cost breakdown based on a typical project scope. Individual quotes may vary.
What affects the price in London
Furnace Efficiency Rating
London's moderate heating season makes high-efficiency furnaces (90+ AFUE) particularly cost-effective over standard 80 AFUE units. With Enbridge natural gas rates around $0.40 per cubic meter, a 95 AFUE condensing furnace can save London homeowners $300-500 annually versus basic efficiency models. High-efficiency units require PVC venting and condensate drains, adding $400-800 to installation costs but qualifying for Enbridge rebates up to $750. London's clay soil conditions may require condensate pump installation in basement installations.
Ductwork Modifications
Many London homes built before 1980 have undersized ductwork or outdated trunk-and-branch systems requiring upgrades for modern furnaces. London's older neighborhoods like Old South and Woodfield feature homes with oil-to-gas conversions needing complete duct redesign. Adding return air ducts or upgrading to larger supply runs costs $800-2,000 but improves comfort and efficiency. London contractors report that 40% of furnace replacements require some ductwork modifications, particularly in century homes near downtown core.
Gas Line Requirements
London homes switching from oil, propane, or electric heating need new natural gas service from Enbridge, adding $1,500-3,000 to project costs. Existing gas homes may require line upgrades to handle higher-capacity furnaces, particularly older 3/4-inch lines feeding 100,000+ BTU units. TSSA regulations require licensed gas fitters for all connections, and London's established gas infrastructure means most residential streets have service available. Gas line work requires separate permits and inspections, extending project timelines by 5-7 business days.
Seasonal Installation Timing
London's heating season runs October through April, creating peak demand for furnace installations in September and October when contractors book 3-4 weeks out. Emergency replacements during January-February cold snaps cost 20-30% more due to urgency and limited contractor availability. London's mild spring weather (May-June) offers the best installation window with competitive pricing and 1-2 week scheduling. Contractors report that pre-season installations in August-September often include promotional pricing and manufacturer rebates.
Home Size and Layout
London's diverse housing stock ranges from compact wartime bungalows requiring 60,000 BTU furnaces to sprawling suburban homes needing 120,000+ BTU capacity. Multi-level homes in areas like Byron and Masonville often need zoned systems or ductwork modifications for proper airflow. London contractors size furnaces based on Manual J load calculations considering the city's 6,800 heating degree days and typical construction methods. Oversized furnaces waste energy while undersized units struggle during London's occasional -20°C cold snaps.
Contractor Availability and Competition
London's robust HVAC market includes over 30 licensed contractors serving the city and surrounding Middlesex County, creating competitive pricing for homeowners. Local companies like those serving the University of Western Ontario area often specialize in specific furnace brands, affecting availability and warranty service. London contractors typically maintain good parts inventory due to the city's size, but specialized high-efficiency components may require 2-3 day ordering from Toronto distributors. Competition keeps labour rates near Ontario's baseline despite London's status as a regional centre.
DIY vs. hiring a contractor
✓ Potential DIY scope
- Furnace replacement in Ontario requires licensed gas technician certification through Technical Standards and Safety Authority (TSSA), making this strictly a professional installation.
- Homeowners can legally disconnect and remove old furnaces, handle ductwork cleaning, and perform basic electrical disconnections with proper safety precautions.
- However, all gas connections, venting work, and electrical hookups must be completed by TSSA-licensed technicians to meet Ontario Building Code requirements.
✗ Requires licensed contractor
- DIY installation of gas appliances risks carbon monoxide exposure, fire hazards, and insurance claim denial.
- Even simple tasks like thermostat wiring should be left to professionals during furnace replacement to ensure proper system integration and warranty coverage.
Tips to save money in London
- Schedule furnace replacement between May and September when London contractors offer competitive rates and 1-2 week turnaround times instead of peak season's 3-4 week delays.
- Contact the City of London building department at 519-661-2489 to understand permit requirements, as TSSA gas permits are separate from municipal building permits for major renovations.
- Verify contractor licensing through TSSA's online database and ensure they carry proper liability insurance, as London's competitive market includes some unlicensed operators.
- Consider high-efficiency furnaces for Enbridge rebates up to $750, which offset the $500-1,000 premium while reducing heating costs in London's 6,800 degree-day climate.
- Get quotes for ductwork inspection and sealing, as London's older homes often have leaky ducts that reduce new furnace efficiency by 15-25% until properly sealed.
Frequently asked questions
How does London's clay soil affect furnace installation costs?
London's heavy clay soil creates drainage challenges for high-efficiency furnace condensate disposal, often requiring condensate pumps costing $200-400. Clay soil prevents natural drainage of acidic condensate that high-efficiency units produce, making pump systems necessary in most basement installations. Some London contractors include condensate pumps in standard high-efficiency quotes, while others charge separately. The clay also affects outdoor venting placement, as contractors must ensure proper grading away from foundations to prevent water infiltration issues common in London's soil conditions.
What rebates are available for London homeowners replacing furnaces?
Enbridge Gas offers London homeowners rebates up to $750 for high-efficiency furnaces (90+ AFUE), plus additional incentives for smart thermostats and ductwork improvements. The federal Canada Greener Homes Grant has closed to new applicants, but existing approved participants can still claim furnace rebates. London Hydro occasionally offers heat pump incentives for electric heating conversions. Manufacturer rebates from companies like Carrier, Lennox, and Trane often provide additional $200-500 savings during spring and fall promotional periods. Combine multiple rebates for maximum savings on high-efficiency installations.
How long does furnace replacement take in London?
Standard furnace replacement in London takes 6-12 hours over 1-2 days, depending on complexity and permit requirements. Simple swap-outs of similar-sized natural gas furnaces often complete in one day, while conversions from oil or extensive ductwork modifications require 2-3 days. TSSA permit processing adds 3-5 business days to project timelines, though contractors often handle applications during pre-work consultations. Emergency replacements can sometimes be completed within 24-48 hours, though permitting may follow installation. London's competitive contractor market generally ensures parts availability without extended delays.
Should I replace my furnace and air conditioner together?
London contractors typically offer package discounts of $500-1,000 for combined furnace and air conditioning replacement, sharing installation labour and electrical connections. Matching systems from the same manufacturer often provide better efficiency and simplified warranty service. However, if your AC unit is less than 8 years old and functioning well, replacing only the furnace makes financial sense. London's moderate cooling season means AC replacement isn't as critical as reliable heating. Consider your current AC's condition, age, and refrigerant type when making this decision.
What size furnace do I need for my London home?
London homes typically require 40-60 BTU per square foot for heating capacity, adjusted for insulation levels, window efficiency, and ceiling heights. A 1,200 square foot bungalow usually needs a 60,000-80,000 BTU furnace, while larger two-story homes may require 100,000-120,000 BTU units. Professional Manual J load calculations account for London's 6,800 heating degree days, prevailing winds, and typical construction methods. Oversized furnaces cycle frequently and waste energy, while undersized units struggle during cold snaps. Licensed contractors should perform detailed load calculations rather than using simple square footage rules.
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How this estimate was calculated
Formula: city_cost = national_baseline × 1.000 × 1.000, rounded to the nearest $50. All costs are pre-tax estimates in CAD. Actual project costs depend on site conditions, scope, and contractor rates.
Cost data last updated: March 2026
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