Second-Floor Pressure Complaint on a 1 in. Service
A two-story house has a 1 in. copper service from a 60 psi municipal main. The meter loses 5 psi at the calculated demand of 30 water supply fixture units. The developed length from the main to the highest lavatory is 110 ft, with 14 psi friction loss in the piping. The highest fixture is 20 ft above the main. The owner complains of weak flow at the second-floor shower. The local requirement is a minimum 8 psi residual at the fixture. A gauge at the meter shows 85 psi static pressure before the PRV.
1. Calculate the available pressure at the highest fixture and determine whether the piping is adequate for the stated minimum.
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Convert elevation to pressure: 20 ft × 0.433 psi/ft = 8.7 psi. Available pressure at the highest fixture = 60 psi main − 5 psi meter loss − 14 psi pipe friction − 8.7 psi elevation = 32.3 psi. That is well above the required 8 psi residual, so the piping is not failing on pressure. The weak shower flow is more likely a fixture valve, aerator, stop, or volume problem rather than insufficient residual pressure.
2. What should you check next if the static pressure at the meter is 85 psi?
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An 85 psi static pressure is high enough to require a pressure-reducing valve in many jurisdictions and can damage fixtures and appliances. Check the PRV setting, downstream pressure, and whether the PRV is functioning. If a PRV is added or already present, the system becomes closed and thermal expansion must be addressed with an expansion tank or equivalent. Also verify that the PRV is not bypassing and that the high static pressure is not masking a partially closed valve or undersized fixture stop.
3. The owner wants to increase the service to 1-1/4 in. to improve shower flow. Is that the best first step?
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No. The calculation shows about 32 psi available at the highest fixture, so the service size is not the limiting factor at the stated demand. Upsizing the service would add cost without addressing the actual restriction. First measure flow and pressure at the shower valve, inspect the cartridge, stops, and showerhead, and compare the actual demand with the assumed 30 fixture units. Only after those checks should piping changes be considered.