Antifreeze in Maryland home sprinkler systems: what changed and what to do with an old loop.

If your house was sprinklered before about 2012 and has heads in the garage, on a screened porch or in a room over an open crawlspace, there is a fair chance a section of that pipe is filled with antifreeze instead of water. It was the standard answer to unheated space for decades, in Montgomery County garages, in Frederick and Carroll County farmhouses, in Annapolis porches. Then the standards changed, and a lot of homeowners never heard about it. Here is what happened and what it means for your system.

Why antifreeze fell out of favor

Sprinkler antifreeze was glycerin or propylene glycol mixed with water, and for a long time nobody paid much attention to how strong the mix was. Then in August 2009 a residential sprinkler in Truckee, California discharged onto a stovetop fire and the spray ignited. The antifreeze concentration in that loop was high enough that the solution burned. A woman died. Testing that followed showed that glycerin and glycol solutions above certain concentrations do exactly that: they flash when they hit a flame.

NFPA moved quickly. Interim amendments capped the concentrations allowed in existing systems, required factory premixed solutions instead of contractors mixing on site, and required new systems to use only antifreeze that has been tested and listed for sprinkler service. NFPA 25, the maintenance standard, then set a deadline: existing systems had until September 30, 2022 to replace any unlisted antifreeze with a listed product or convert to another method. That date has passed. An old glycerin loop in a Maryland garage is now out of compliance with the standard your annual inspection is performed to.

How to tell if you have one

• Look at the riser. An antifreeze loop connects to the wet system through a separate valve, usually with a small expansion chamber and a fill cup or test connection nearby. If the riser has a second control valve tagged for the garage or porch, that is the loop.
• Read the tag. Inspectors are supposed to test the solution every year with a refractometer or hydrometer and record the freeze point on the inspection tag. A tag that lists a specific gravity or a freeze temperature is telling you there is antifreeze in the system.
• Check the heads. Antifreeze protected areas use ordinary wet heads. If the garage heads are the long barrel dry sidewall type, or the pipe drops into the garage from a heated wall, the system was probably designed without antifreeze and you can stop reading here. Our article on attics and garages explains what those dry heads are doing.
• Ask. A system that has been inspected annually will have a report that says so. If nobody has looked at the system in years, book a checkup and ask the technician the question directly.

What you cannot do

Do not top off a loop with whatever is on the garage shelf. Automotive antifreeze is ethylene glycol, which is toxic and was never permitted in a sprinkler system. Even the right chemical at the wrong strength is the exact problem the standards were written to remove. And if your house has a multipurpose 13D system, the kind where the sprinkler pipe and the domestic water share one network, there should be no antifreeze anywhere in it. That pipe feeds your kitchen tap. Our how sprinklers work guide explains how to tell a multipurpose system from a standalone one.

The three ways a loop gets replaced

• Listed antifreeze. The loop stays. It is drained and flushed, then refilled with a factory premixed solution that carries a listing for sprinkler use. This is the least disruptive option and the one that keeps the annual freeze point test on the schedule. It is also the option most limited by the listing itself: listed solutions come with pressure and volume restrictions, and some loops in older houses are too large or run at too high a pressure to qualify. We check the design before recommending it.
• Dry sidewall heads. The loop comes out and the garage or porch is covered by dry heads fed from pipe inside the heated envelope. The barrel of a dry head holds a plug that keeps water back in the warm side of the wall until the head opens. This is what Montgomery County now expects in garages under living space, and it is our default for any garage in the state. No chemical, no annual solution test, nothing to freeze.
• Move the pipe. Sometimes the loop exists only because the original installer ran pipe through an unheated chase or an uninsulated attic corner. Rerouting that run into conditioned space, or insulating it correctly on the warm side, removes the reason for antifreeze in the first place. Our winter freeze proofing guide covers where Maryland pipe actually freezes.

Every one of these is a permit job in the counties we work in, because each one changes heads or pipe on a life safety system. That is not a reason to put it off. It is the reason to have a licensed sprinkler contractor do it rather than a plumber, so the record stays clean for the next sale.

What it costs

The site publishes ranges for full systems, not for loop conversions, because the spread is too wide to be honest about in a table. A small porch loop refilled with listed solution is a short visit. A three car garage converted to dry sidewalls off a new run from the basement is a day of work plus heads and pipe. We quote each one after seeing the riser and the space. Where a conversion turns into repiping a whole area, our published retrofit range of $2 to $7 per square foot for that area is the right frame; a garage with an open ceiling sits at the low end.

If the loop has already frozen once

Weak antifreeze freezes. A loop that was topped off with plain water for years will slush up in a hard January, and a slushed loop that thaws can leave a cracked fitting that only shows itself in spring. If the garage heads have ever dripped after a cold snap, or the riser gauge dropped over the winter with no other explanation, tell the inspector. That system needs a pressure check on the loop before anyone decides which of the three options fits it.

The good news is that this is a known problem with a known fix. Most of the antifreeze loops still in Maryland houses are there because nobody told the owner the rules changed. Now you know.