High-efficiency furnaces use PVC pipes for venting because they operate at lower exhaust temperatures and produce highly acidic moisture. Traditional metal flues would quickly corrode, but PVC resists this acid while being perfectly suited for cooler gases.
All that water vapor in the cool exhaust condensates into acidic liquid that would eat through metal pipes faster than you can say "expensive repair." That's why high-efficiency furnaces use PVC or CPVC pipes - they can handle the acidic condensate without breaking down.
Newer furnaces are 50–60% more efficient than they were 30+ years ago, so you will immediately start to see lower energy bills after installation.
High-efficiency furnaces use PVC pipes to vent the exhaust gases out of the home, and manufacturers are very specific about how the installation should be done.
PVC is designed for applications where temperatures will not exceed 140°F (60°C). Exposure to higher temperatures can cause the material to warp, soften, or become brittle, leading to cracks and system failure.
PVC pipes have significant disadvantages, including low heat resistance, brittleness in cold, and environmental toxicity. They are unsuitable for hot water systems, prone to cracking under high pressure or impact, and can release toxic chemicals, such as dioxins and vinyl chloride, during production, use, or disposal.
In HVAC duct design, the two-foot rule is a guideline stating that branch ducts (takeoffs) must be placed at least 24 inches away from any air direction change, transition, or end cap. This spacing allows turbulent air to re-pressurize and stabilize, ensuring consistent airflow to every room.
The best time to buy a furnace is during the off-season, specifically late spring (April-May) or early autumn (September-October), when HVAC companies are less busy and offer lower prices, rebates, or promotions. Purchasing in these shoulder seasons ensures faster installation times and better negotiating power compared to winter peak season.
While PVC is less expensive than cast iron piping, it may not automatically be the right decision for your home. If you have existing cast iron plumbing, you may want any repairs or replacements to also use cast iron for consistent performance and longevity.
Two PVC pipes coming out of a furnace, typically 2-inch diameter, are for a high-efficiency (90%+ AFUE) furnace, with one acting as a fresh air intake and the other as an exhaust vent. These pipes are essential for combustion, safety, and efficiency. They may exit side-by-side or with the exhaust higher and farther out to prevent re-breathing exhaust fumes.
The Basics of The New Gas Furnace Mandate
While the current standard AFUE (Annual Fuel Utilization Efficiency) for a residential furnace is 80%, this mandate will require all gas furnaces to maintain a fuel efficiency rating of 95%.
An 80,000 BTU furnace typically heats homes ranging from 1,600 to 2,500 square feet. The exact coverage depends heavily on your local climate, ceiling height, insulation quality, and the overall energy efficiency of the furnace.
The $5,000 rule is a guideline to help homeowners decide whether to repair or replace their HVAC system. You multiply the age of your unit by the cost of the needed repair. If that number exceeds $5,000, replacing your HVAC system is often more cost-effective.
Yes, you can vent a high-efficiency (condensing) furnace through the roof. While many modern installations use a sidewall, routing the plastic (PVC/CPVC) exhaust and intake pipes vertically through the roof is a standard and frequently used alternative.
5 Warning Signs It's Time for Furnace Replacement
The last cast iron sewer pipes were installed in American homes in the early 1980s. Most areas stopped using cast iron by the 1970s. Here's why cast iron fell out of use in residential sewer systems: Cost.
Average Cost to Replumb a 1,500 Square Foot House
Most homeowners pay between $4,500 and $8,500 for a PEX repipe. Copper repiping costs more. Expect to pay $9,000 to $12,000 or higher for copper pipes in a home this size.
The "135-degree rule" in plumbing states that the total (aggregate) horizontal change in direction for a drainage pipe—specifically trap arms—cannot exceed 135 degrees between the P-trap and the vent. Exceeding 135 degrees (such as using three 45-degree bends or a 90 and two 45s) requires a cleanout because sharp turns hinder flow and cause clogs.
Yes HVAC prices have steadily increased over the past few years, and 2026 is no exception. These increases are affecting everything from entry-level systems to high-efficiency units, making it more expensive than ever to install or replace HVAC systems.
You should probably Replace if: [ ] The repair costs more than 50% of a new unit. [ ] The furnace is over 15 years old. [ ] You have had to repair it more than once in the last 2 years.
In short, the 20-degree rule of air conditioning states that you should always keep your AC unit at no more than 20 degrees lower than the outside temperature. It means that, if the outdoor conditions are at 95 degrees, you should set your thermostat at no less than 75 degrees.
One of the most common mistakes in HVAC duct fabrication is incorrect measurements. Ducts that are too small or too large for the system or the home will lead to airflow restrictions, energy inefficiencies, and increased noise levels.
One of the most surprising places they can hide? Your ductwork. That's right: your heating and ventilation system may be more than just a pathway for warm or cool air; it could also be a cozy travel route (and nesting spot) for mice.
The answer: neither is ideal. Properly sized ductwork helps your system move air efficiently, keeps your home comfortable, and prevents unnecessary strain on your equipment.