Furnace Venting Explained: Chimney vs. PVC for Minnesota Homes

If you're building a new home in Minnesota or upgrading an existing furnace, understanding venting is essential. The type of venting determines where you can place the furnace, how exhaust exits, and which models work for your situation.

Standard Efficiency Venting (80% AFUE)

Standard 80% AFUE furnaces produce exhaust at 350–450°F that naturally drafts upward through metal flue pipe (Type B vent) or a masonry chimney. An inducer fan ensures consistent draft. The exhaust exits through the roof.

Requirements

• Vertical Type B vent or lined masonry chimney
• Proper clearances from combustibles (1 inch for B-vent)
• Adequate chimney height for draft
• Combustion air supply from surrounding space or dedicated intakes

High-Efficiency Venting (90%+ AFUE)

Condensing furnaces (90–97% AFUE) cool exhaust below the dew point, creating condensation. Exhaust temperature is only 100–150°F — too cool for natural draft and too corrosive for metal chimneys. These use PVC pipe venting instead.

Direct Vent (Two-Pipe) — Preferred

Two PVC pipes: one exhaust out, one combustion air in. The furnace is sealed from indoor air. Best for tight, efficient homes and confined spaces.

Single-Pipe Vent

One PVC pipe for exhaust. Furnace draws combustion air from surrounding indoor space. Works for open basements with adequate volume.

Comparison

Minnesota-Specific Venting Challenges

Frozen PVC Vent Terminations

During extreme cold, moisture in PVC exhaust can form ice at the exterior termination point. If enough ice builds up to block the vent, the pressure switch shuts down the furnace. This is one of the most common cold-weather furnace failures in Minnesota.

Prevention: install the termination at least 12 inches above expected snow line, use proper termination fittings, keep the area clear of snow and ice, and check during extreme cold snaps.

Snow Burial

Side-wall vents at low height can get buried by heavy snowfall, causing shutdown. After major storms, always check your furnace vents are clear — 30 seconds of effort prevents a midnight failure.

Chimney Orphaning

Upgrading from 80% to 96% AFUE leaves the water heater as the only chimney user. An oversized chimney for one appliance causes draft problems and potential CO issues. Your installer should evaluate and potentially reline the chimney.

Which Venting for Your Situation?

Choose 80% (Chimney) If:

• You have a good existing chimney and want a direct swap
• Running new PVC isn't practical in your layout
• Budget is the top priority

Choose 96% (PVC) If:

• You're building new or have flexibility
• You want lowest operating costs ($200–$400/yr savings)
• Minnesota's long heating season makes the efficiency payback faster

At Furnace Direct, we carry both 80% and 96% AFUE Goodman furnaces. For Minnesota, we recommend 96% for most installations — the savings pay back within 3–5 years. PVC venting is cheaper in materials than metal chimney venting. Same-day Twin Cities metro delivery for orders before 3 PM CT at factory-direct pricing.