Replacing the water heater or repiping a sprinklered house: what your plumber has to know first

A tank water heater lasts 10 to 15 years, which means a 2005 townhouse in Ashburn or Manassas is on its second one and a 1995 townhouse in Burke is on its third. The plumber arrives, shuts the main, drains the tank, and gets to work in a utility room where the sprinkler riser is standing two feet away. Most of the time nothing goes wrong. The calls we get are from the other times, and nearly every one traces back to one of three things: a valve closed and left closed, a device added on the wrong side of the sprinkler tee, or a repipe that treated the sprinkler pipe as plumbing. This article is the conversation to have with the plumber before the old heater comes out.

First, know which system you have

Look at the riser. If it has its own control valve, a check valve, a gauge, and a drain, with the sprinkler pipe leaving as its own line, the system is standalone. If the sprinkler heads hang off the same CPVC or PEX that feeds the bathrooms, with no separate riser, it is multipurpose. The multipurpose versus standalone article explains the difference and the riser parts article labels each piece. Almost every retrofit and most of the 1990s and 2000s townhouses are standalone. The plumber's job is different for each, so this is the first thing to tell them.

A standalone system and a new water heater

On a standalone system the sprinkler tee comes off the service before the water heater, and the sprinkler line carries cold water only. A plumber replacing a water heater never touches the fire system, and should not have a reason to. Three things still matter.

• The house main shuts the sprinklers off too. The main valve sits upstream of the sprinkler tee, so while the plumber has it closed the house has no fire protection. For a half day that is acceptable. If the job runs into a second day, the main goes back on overnight.
• The sprinkler control valve stays open. Plumbers close every valve they can find to drain a system, and the sprinkler control valve looks like one more. Ask them to leave it alone, and check it is open before they leave. A closed control valve is how a sprinklered house burns, and the everyday care article names it as the most common thing a trade leaves wrong.
• If the sprinkler drain got opened, the system needs a refill. A drained sprinkler system refills from the main, but the air has to bleed at the highest head and the refill has to go slowly or the flow switch rings the bell. If the system is monitored, the monitoring article explains why a fast refill calls the central station. That refill is our visit, not the plumber's.

A multipurpose system and a new water heater

On a multipurpose system the heads sit on the cold water loop, and the water heater is downstream of them. A like for like tank swap is routine. The trouble starts with what plumbers add during a swap, because a modern water heater install often brings a pressure reducing valve, an expansion tank, and sometimes a whole house filter with it.

The rule is simple to say and easy to forget: nothing goes on the cold line upstream of the sprinkler loop without the design being checked. A pressure reducing valve set to 60 psi ahead of the loop takes pressure the hydraulic calculation was counting on. A filter or softener adds friction loss the calculation did not include. The softener and PRV article goes through each device and where it may sit. An expansion tank is the one that is always fine, because it belongs on the heater's cold inlet, downstream of the loop, and does not change what reaches the heads.

Tankless heaters

A tankless unit changes two things that matter. It hangs on a wall, usually a different wall from where the tank stood, so the plumber reroutes the cold feed to reach it. On a standalone system that reroute must leave the sprinkler tee as the first branch off the service, before the new run to the heater. On a multipurpose system the heater's new location must stay downstream of the last head on the loop. The second thing is a recirculation pump, which some tankless installs add. It belongs on the hot side and the return and never on the loop that feeds heads. Tell the plumber those two sentences and a tankless install is as uneventful as a tank.

A repipe is a different job

Houses with gray polybutylene or rusted galvanized get repiped, and the polybutylene article explains why a sprinkler contractor insists on it. The repipe itself splits by system type.

• Standalone. The sprinkler piping is its own system and stays. The plumber replaces the domestic piping and reconnects the service to the sprinkler tee, and we come out to confirm the tee, the riser, and the pressure after the new service is live. One visit.
• Multipurpose. The sprinkler piping is the domestic piping. Replacing it means replacing the sprinkler system, which is a sprinkler permit with a new hydraulic calculation, done by a contractor whose DPOR license carries the fire sprinkler specialty. A plumbing license alone does not cover it, and the license lookup article shows how to check. In Fairfax, Loudoun, and Prince William the sprinkler permit rides with the plumbing permit, and the county inspects the rough before the walls close.

The five lines to hand the plumber

• This house has a fire sprinkler system. The riser is in the utility room, and the control valve on it stays open.
• Shut the house main for the work and reopen it before you leave each day.
• Do not open the sprinkler drain. If it opens, tell me, because the system has to be refilled by the sprinkler contractor.
• Nothing new goes on the cold line ahead of the sprinkler tee or loop, no pressure reducing valve, no filter, no softener, without a call first.
• A tankless or a repipe changes where the tee sits. Send me the plan before you cut.

After the plumber leaves

Walk to the riser. The control valve handle should be in line with the pipe, the gauge should read the same street pressure it read last month, and nothing should drip at the fittings. If the gauge reads zero, the control valve is closed or the system drained, and either one is a call today, not next week. If the bell rang during the refill, the bell ringing article explains the three minute check. If the plumber cut or capped a sprinkler line to make room for the new heater, the contractor hit the pipe article covers who fixes it and who pays.

A check visit after a repipe or a tankless install is a service call at the flat visit rate on the inspection page. A water heater swap on a standalone system with the control valve left open needs no visit at all. County details live on the Fairfax County guide, Loudoun guide, Arlington and Alexandria guide, and Prince William guide.