1 1/2 vs 2 Inch Drain for Your Kitchen Sink - Making the Best Choice

When installing or replacing a kitchen sink, one decision that arises is what size drain pipe to use. The two most common options are either a 1 1/2 inch or 2 inch diameter drain line. But how do you determine which is the best choice for your specific kitchen?

This includes assessing your local plumbing codes, sink usage, drain line length, possibility of clogs, and more. We'll also look at the differences in water flow rate, installation complexity, and cost between the two sizes.

Checking Your Regional Plumbing Codes

The first thing to look at when choosing a new kitchen sink drain size is your local and regional plumbing codes. These building codes and regulations determine the minimum drain line diameters permitted for residential kitchen sink drains based on variables like number of fixtures, drain length, and pipe material.

For example, older plumbing codes may still allow for 1 1/4 or 1 1/2 inch drain lines. However, newer codes tend to mandate either 1 1/2 inch or 2 inches as the minimum size. Many areas have updated codes to prevent clogs and improve flow rate. Failure to comply with the applicable codes could result in fines, removal and replacement of undersized piping, or refusal to approve the plumbing inspection.

Why Drain Line Codes Matter

Beyond just meeting the minimum legal requirements, there are good reasons why plumbing codes have trended towards larger pipe diameters for key household drainage lines like kitchen sinks.

Larger drain pipes improve water flow, decrease odds of obstructions, allow more gallons per minute of discharge, and reduce backups of dirty water - key considerations for a highly utilized fixture like a kitchen sink.

Weighing Drain Line Capacity and Flow

When evaluating kitchen sink drain sizes, an important performance factor is the capacity and flow rate of the drain line. Capacity refers to how much liquid the pipe can effectively transport to the main sewer line. Flow rate measures how quickly water drains out of the sink.

In both metrics - capacity and flow - a 2 inch diameter pipe outperforms a 1 1/2 inch pipe. The cross sectional area of a 2 inch drain line is 1.96 square inches, over 50% more than the 1.23 square inch area of a 1 1/2 inch pipe. This directly correlates to more gallons per minute that can drain through a 2 inch line.

Real-World Performance Differences

However, for many residential kitchen sinks, a 1 1/2 inch drain pipe provides adequate capacity and flow. While the 2 inch line has higher potential throughput, actual water volumes from an average home kitchen faucet are often modest and easily handled by a smaller drain. Upwards of 30 gallons per minute can drain through a new, properly pitched 1 1/2 inch pipe with no obstructions - more than enough for a typical sink.

The choice comes down to balancing pipe flow rates against complexity of installing a larger 2 inch diameter pipe. If your particular kitchen sink gets heavy duty usage - like canning, brewing beer, constant food prep, etc - opting for the 2 inch drain offers extra capacity.

Checking Sink Compatibility

Another consideration when choosing between a 1 1/2 vs 2 inch kitchen sink drain line is compatibility with the actual sink itself. Many modern sinks are designed and manufactured with a 2 inch diameter drain hole and tailpiece. Attempting to squeeze a smaller 1 1/2 inch pipe into an opening made for 2 inches requires adapters which may lead to leaks or drainage issues.

Always check your sink documentation for the recommended or required drain size. For example, some extra deep and heavy duty sinks for serious home cooks mandate a 2 inch drain fixture. Trying to jam in an incompatible sized pipe against the product specifications is asking for trouble down the road.

Issues From Size Mismatch

Potential problems from connecting a 1 1/2 inch drain pipe to a sink with a 2 inch built-in drain include: insufficient water flow, gurgling sounds, excessive vibration, regular clogging from food debris designed to fit the wider drain, and persistent leaks requiring plumbers putty or sealant to patch around the smaller pipe.

Variables That Impact Drain Efficiency

There are several other factors besides just pipe diameter that affect overall drain effectiveness and likelihood of clogs:

• Length of the drain pipe run
• Presence of a garbage disposal
• Adequate venting
• Proper P-trap installation
• Correct slope or pitch

A longer horizontal drain pipe with marginal slope, crammed sharp bends, and a 90 degree elbow directly under the vertical pipe will drain far worse than an optimized 2 inch pipe. Meanwhile, a short, straight 1 1/2 inch line with venting and a disposal can outperform a janky 2 inch drain. Pipe size is just one piece of the puzzle.

Clogs and Obstructions

In terms of reducing clogs from food waste and debris, a 2 inch kitchen sink drain pipe is theoretically less prone to obstructions. The wider diameter allows more solids to pass through without getting caught in traps or elbows. However, a properly installed 1 1/2 inch drain line receives adequate scouring action for typical residential kitchen usage.

Regularly pouring grease or scraps down any drain pipe inevitably causes buildup and blockage over time, regardless of size. Proper habits - like scraping plates and using strainers - combined with occasional drain maintenence extends the lifetime of even a 1 1/2 inch kitchen pipe.

Comparing Installation and Costs

When estimating the overall budget for a remodeled kitchen with a new sink, the drain installation is a major factor. Typical costs for a professional plumber to install a basic kitchen sink drain pipe start around $175-225. This typically covers up to 10 feet of plastic or copper 1 1/2 inch pipe, P-trap, fittings, strainer, seals, and labor.

Opting for a 2 inch drain line does incur more expense in materials - potentially $50-100 depending on length. The pipes, elbows, fittings and other components cost marginally more than their 1 1/2 counterparts from the plumbing supplier. But the labor is essentially equivalent for a professional plumber installing either diameter pipe. If tackling the job as a DIY project, stick with 1 1/2 inch components which are easier for amateur installations in tight sink cabinets.

Complexity and Access Issues

One other consideration with 2 inch drains is added complexity working in the confined space under a sink. The larger fittings are tougher to maneuver, thread, and seal up. Without professional tools or skills, an amateur installation could easily result in leaks that then damage cabinets or flooring. There also tends to be fewer options for elbows, trap adapters, and connectors available at hardware stores for 2 inch pipe versus the universally stocked 1 1/2 inch components.

When it comes to deciding between a 1 1/2 vs 2 inch drain line for your new or renovated kitchen sink, there are many factors at play. The usage level and water volumes expected, compatibility with your selected sink basin, ease of installation, susceptibility to clogs, and meeting local building codes should all weigh on the decision.

In summary, here are some general recommendations:

• Standard home kitchen - 1 1/2 inch likely sufficient
• Heavy usage/entertaining kitchen - 2 inch better
• Concern over clogs - 2 inch less prone to obstructions
• Shorter drain line - 1 1/2 inch adequate
• DIY install - stick with 1 1/2 inch components
• Modern sink with 2" tailpiece - match drain size to sink
• Older home with cast iron plumbing - 1 1/2 inch likely code minimum

As with any home improvement project, understand all the variables before deciding. Consult local codes, evaluate your specific kitchen usage, inspect the sink model specifications, and solicit professional opinions from plumbers or contractors. This helps guarantee you select the optimal drain line solution.