Insulated PEX Pipe: Am I Losing Heat Underground?

Insulated PEX Pipe: Am I Losing Heat Underground?

If you think that you are losing heat underground we can help you troubleshoot what could be the problem. There are several possible reasons why you are losing heat. 

Here are the possible causes, and the recommended solutions:

1) You may be losing heat underground because you have low-quality pipe

Low-quality components will not provide the insulation value you need to prevent heat loss.

Click HERE to watch this video and upgrade!

.2) You recently installed your underground pipe

This is NOT lost heat from your underground pipe, but rather heat escaping from the earth via the path of least resistance - the earth you disturbed while trenching.

This will go away after the ground settles. You can do the Delta-T Test just to be sure.

.3) You are losing heat underground because you have a LEAK in your outer casing

Water fills the outer casing, sucks heat away from your PEX tubing, and that heat gets absorbed by the earth - and the earth can absorb an infinite amount of heat!

Click HERE to watch this video for an explanation.

Try This Simple Test...

You can check your underground insulated pex pipe for heat loss in about 5 minutes. This is called a “Delta-T” test which is simply a measurement of how much heat is lost through your underground pipes into the earth, or the air. The instructions for the Delta-T test are as follows:

  1. MAKE SURE ALL LOAD IS TURNED OFF.  All unit heaters and furnaces must be disabled, and no hot water faucets can be open during the test. Make sure nobody is taking a shower, and your outdoor wood furnace blower fan is off, otherwise, the test results are useless.
  2. Using a digital thermometer, take temp readings at the back of the furnace on BOTH the Feed Line and Return Line.
  3. When taking readings, apply temp sensor, cover with insulation, and secure in place with Velcro or tie strap. Make sure the sensor is touching a metal surface. Leave attached at least 90 seconds or until temp stops rising on the readout display, whichever is later.
  4. For FEED LINE, apply temp sensor to fitting or pipe close to furnace back wall. We want the true furnace water jacket temp, before any heat loss from the pipe.
  5. For RETURN LINE, apply temp sensor to fitting or pipe at least 4 inches from your outdoor wood boiler body. We want the temp coming back from the line before it mixes with the water in the water jacket.
  6. Do NOT use an infrared thermometer on PEX or PAP tubing. It will not give an accurate reading. An Infrared thermometer can only get accurate readings on metal fittings or pipes.
  7. Record these readings. If you see temp differences larger than one degree per 100 feet of underground pipe, you are experiencing larger heat loss than is acceptable.

If your heat loss is TOO HIGH, you should consider replacing your pex underground. Be sure to only use Heat Mizer brand insulated underground pex from so you can maximize your savings for decades.

Troubleshooting FAQs:

  • Why am I not getting hot water?

Check that the hot water system is connected properly. Check if the heat exchanger is partially or totally clogged.

  • I can't find a leak in my outdoor wood burner. Why am I losing water?

The furnace uses a non-pressurized system, this means that the system is exposed to the air. Since the water in the system can and will be warmer than the air, there will be evaporation of the water in the system. The water must be checked and adjusted at least once a month, sometimes more.

  • Why does smoke come out through my door?

There are several adjustments that you can make to the door. Your door seal may be worn and need replacement. The seal usually needs to be replaced about every 2-3 years. It may be sooner if the wood is too close to the door in the firebox.

  • My Outdoor Furnace stopped running what should I do?

Check if there is there power to the furnace? Does the light work?

Check the high limit switch? Is the blower and or solenoid working? Are the wires in good condition?

  • My Outdoor Wood Stove is leaking, What do I do?

Inspect the thermometer well, the Aquastat well, the drain plug, the factory-mounted feed plug, and the return cap, as well as any other fittings added in the field for leaks. Loose fittings are the most common cause of Leaky furnaces.

Contact for more information M-F from 9 am-8 pm at (231) 861 8200. And to check for more outdoor wood boiler parts visit our online store.