Hot water jetting usually clears grease lines better. Heat softens and melts grease so the jet can strip it off the pipe wall and flush it out, where cold water tends to push it downstream. The water still has to be sized to the line, the pipe has to tolerate the heat, and the grease needs somewhere safe to land.
What hot water does to grease
Grease in a kitchen line starts as a hot liquid and hardens as the wastewater cools. Over months it builds a layer on the pipe wall. A cold jet can scour that layer with force. In fact, one sewer equipment supplier says 18 GPM at 4,000 PSI breaks grease into sand-like particles that flow downstream. So cold jetting works on grease, and pressure and flow do real work.
Hot water adds a second mechanism. HotJet, a hot-water jetter maker, says that at 140°F and above, grease transitions from a solid or semi-solid state back into a liquid. In its words, cold water "just pushes it downstream," while hot water "melts it off the pipe walls and flushes it out as liquid waste." Machines sold for this work heat water as high as 210°F, at flow rates of 10 to 20 GPM and pressures up to 4,000 PSI.
The practical effect is on old, hard deposits. A coating that took years to build resists a cold jet, and a nozzle can skip over the thickest parts. Heat softens those spots so the rotating head can finish the job. A sensible order on a grease-clogged kitchen line is a penetrating head to open the line first, then a rotating head with hot water to clean the wall on the second pass. Our page on what the different nozzles do covers the order.
Where hot water falls short
It cannot fix a line that is undersized for the flow. HotJet's guidance for grease lines is a minimum of about 8 GPM for 4-inch to 6-inch lines, and it says pressure matters less than flow. A hot stream with too little volume melts grease and then leaves it in the pipe to cool. See PSI versus GPM.
Pipe material limits the heat. Plastic pipe and fittings have temperature ratings, and machines that heat water to 210°F can exceed them, so the crew has to know the pipe material and keep the water hot enough to melt grease but safe for the plumbing. Older lines add their own risks, so read whether jetting can damage old pipe first.
Melted grease still has to go somewhere. This is the caution that matters most. Cities that run FOG programs warn that hot water does not solve the grease problem by itself. Fountain Valley says that adding hot water, detergent, or even commercial degreasers "does not liquefy the grease long enough to escape your drains." Gwinnett County adds that grease can start to harden again before it leaves your house plumbing or your sewer lateral. The same physics apply to a jetter. If melted grease is flushed past your interceptor or out to the public sewer, it can cool and stick further down the line.
That is why a good grease-line job is planned around the grease interceptor, not just the kitchen line. Debris from the kitchen line should land where the system is built to catch it, and the interceptor should be pumped on schedule so it can keep catching. Our page on Phoenix's rules on enzyme and grease-dissolving treatments explains why cities treat products that push grease past an interceptor as a problem, and how often to pump a grease trap covers the schedule.
When heat is worth asking for
| Problem | Does heat help? |
|---|---|
| Old, thick grease coating on a kitchen branch or main | Yes, this is where it earns its keep |
| A line that keeps backing up after cold jetting or snaking | Worth trying, and worth a camera to see what is left |
| Fresh, light grease film | Cold jetting with enough flow usually does the job |
| Tree roots | No. Roots are a cutting job, not a melting job |
| Hard mineral scale or rust | No. Scale needs mechanical tools, see cast iron descaling |
| Sand, grit, and loose debris | Flow matters more than temperature |
Grease is the problem heat solves. If the camera shows a different problem, a hot stream will not fix it. That is one more reason the camera comes before the jetter on any line you have not worked on before.
A word on the hot water your staff pours. Kitchen crews often flush drains with hot water at closing, and some run degreasers or enzyme products on top of it. That habit does not do the work of a jetter. City programs say the opposite: adding hot water, detergent, or degreasers does not liquefy grease long enough to keep it from hardening farther down. An end-of-day flush can help keep a strainer clear, but it is no replacement for scheduled jetting or for pumping the interceptor.
A picture of a well-run grease-line job, as an example. A restaurant's kitchen branch has been backing up every few weeks. The crew cameras it and finds a thick grease coating over a long run. They open the line with a penetrating head, follow with a rotating head and hot water at the flow the pipe needs, and flush. A second camera pass shows a clean wall. The manager schedules the interceptor pump-out for the same week and puts the branch on a quarterly cleaning list. The result is a line that stays open because the coating is gone and the trap can do its job, not because one clog was cleared.
How hot jetting compares with snaking and cold jetting
A cable machine bores a hole through grease and leaves the coating on the walls. Our page on why kitchen drains keep overflowing covers that in detail. Cold jetting cleans the wall, and hot jetting cleans it faster and more completely when the deposit is old. A camera pass afterward is the step that turns a claim of a clean line into proof. It also shows whether the heat did what it was supposed to do. If the wall is still coated, the crew can make another pass while they are on site, and if the pipe shows damage, the answer is repair, not more water. That is why we treat the camera as part of the job and not an extra. Either way, keep the video with your building records, so the next crew knows what the line looked like and how fast it filled last time.
What to ask a plumber, and what it means for a restaurant
- Do you carry hot water for grease lines, and what temperature will you run?
- What is the pipe material, and is it rated for that temperature?
- What GPM will you use for a line this size?
- Where will the loosened grease go, and when should the interceptor be pumped?
- Will you camera the line afterward?
HQ offers hydro jetting and commercial drain cleaning for restaurant lines, with free estimates and the price given up front, before work starts. If your kitchen line keeps returning, the right combination is usually a scheduled jetting, a pumped interceptor, and staff habits that keep grease out of the sink. See what FOG is for the basics.