Cutting round ductwork requires precision and the right tools. A duct cutter, specifically designed for circular ducts, is ideal. First, mark the cutting line on the duct using a measuring tape and pencil. Then, position the duct cutter's blade on the marked line. Apply steady pressure, rotating the cutter around the duct. The sharp blade creates a clean, precise cut. Alternatively, a reciprocating saw with a metal-cutting blade can be used for larger round ducts. Ensure the duct is securely held in place while making the cut to prevent slips and maintain accuracy.

Since water heaters are primarily made of metal, they’re commonly accepted by scrap yards and collectors. Don’t expect to fetch a high price, though—water heaters are mostly steel and aluminum, which aren’t high-value metals. Some components are made of more valuable metals, like brass and copper, but they’re a small portion of the heater and won’t affect the price much.

Yes, you can use a saw to cut metal pipes. The best saw to use is a reciprocating saw, but even a fine-tooth hacksaw can get the job done. No matter which saw you use to cut metal pipes, wear protective gear, like work gloves, safety goggles, and ear plugs. Apply a firm, steady pressure to the tool, and always ensure the pipes are secured so they don't move while you make the cuts.

Cutting rectangular ductwork requires careful measurements and the right technique. Use a measuring tape and pencil to mark the cutting lines accurately. Tin snips are excellent for straight cuts on smaller ducts. For more extensive or thicker rectangular ducts, a reciprocating saw with a metal-cutting blade is effective. 

Ensure the duct is well-supported and secure while cutting to prevent wobbling and maintain precision. After cutting, use a metal file to smooth any sharp edges, ensuring safety during installation.