Master bath is on the far end of the house from the water heater, about 70 feet of pipe.

No, there is no code maximum distance between the water heater and a fixture in the IRC, IPC, or UPC.

*What is regulated (2021/2024 IRC §P2905 / IPC §607 / UPC §607):*

1. Volume/Time Limit: Hot water must arrive at the fixture within a set time/volume to prevent waste. IRC/IPC: ≤ 0.5 gallons (≈ 50 ft of ½" PEX/Copper) from source to fixture. UPC: ≤ 0.25 gallons (≈ 25 ft of ½" tube) for public lavs; ≤ 0.5 gal for others.
2. Pipe Sizing: 70 ft requires upsizing (typically ¾" trunk to ½" branches) to maintain pressure/flow per sizing tables (IRC Table P2903.6 / IPC Table 604.5).

Your 70-ft Reality Check:

• ½" Pipe: Holds ~1.2 gal. Fails code (2.4x IRC limit). Wait time: 60–90+ seconds.
• ¾" Pipe: Holds ~2.7 gal. Fails worse. Wait time: 2+ minutes.

Code-Compliant Fixes (pick one):

1. Demand Recirculation Pump (IRC P2905.2 / IPC 607.2.1): Push button/motion sensor activates pump only when needed. Returns cooled water to heater via cold line (dedicated return preferred). Best retrofit.
2. Point-of-Use Tankless at master bath: Eliminates run entirely. Requires 240V/60A+ circuit.
3. Structured Plumbing / Home Run Manifold with ⅜" PEX (IRC P2903.5): ⅜" holds 0.06 gal/ft → 70 ft = 0.42 gal (Passes). Requires manifold near heater; ⅜" only for single fixtures (lavs/showers need ½").

Do not run a continuous recirc loop without a timer/aquastat and insulation—it wastes massive energy and may violate energy codes (IECC §R403.5.1.1).

Bottom line: Distance is legal; the delay isn't. Install a demand recirc pump (e.g., Grundfos Comfort, Watts 500800) or re-pipe with ⅜" home-runs.

There is no specific code limit on the maximum distance hot water can run from a water heater to a fixture under the International Residential Code (IRC) or Uniform Plumbing Code (UPC). However, practical and efficiency considerations apply.

The IRC (Section P2903.5) and UPC (Section 609.4) require that hot water be delivered to fixtures within a reasonable time to avoid excessive water waste while waiting for hot water. While no hard distance limit exists, the U.S. Department of Energy and ASHRAE 90.2 recommend that the hot water supply line from the water heater to the farthest fixture should not exceed 50 feet for optimal energy and water efficiency — especially in residential applications.

At 70 feet, you’re exceeding this recommendation. This can lead to:

• Significant wait times for hot water (wasting water and energy),
• Increased heat loss in uninsulated pipes,
• Potential for lukewarm water at the fixture.

Practical solutions (not code-required but strongly advised):

• Insulate hot water pipes (minimum R-4 insulation per IRC N1103.2.1 / UPC 609.4).
• Install a recirculation system (with a timer or demand-controlled pump) to keep hot water moving.
• Consider a point-of-use tankless water heater near the master bath for instant hot water.
• Use larger diameter pipe (e.g., 3/4" instead of 1/2") only if justified by flow calculations — oversizing can worsen wait times.

Bottom line: No code prohibits 70 ft, but it’s inefficient. Insulate pipes and consider a recirculation system or point-of-use heater to meet performance and conservation goals. If unsure, consult a licensed plumber — especially if modifying piping or adding mechanical systems.

Note: Always verify local amendments — some jurisdictions (e.g., California Title 24) enforce stricter hot water delivery limits.