utilizing combustion analyzer to diagnose condensing furnace drain points

Set up a take a look at port into the exhaust pipe, a minimal of 12 inches away from the inducer outlet. That is sometimes a 3/8-in. opening however can fluctuate in measurement relying in your analyzer probe diameter and take a look at plug measurement. Should you stay in an space the place putting in a take a look at port within the exhaust is towards code, you may measure on the exhaust penetration of a sidewall termination. For the remainder of the article, we’ll assume you may take a look at on the furnace.

Flip your combustion analyzer on open air and permit it to zero out, then come again inside and insert the analyzer probe into the exhaust pipe take a look at port.

Set the thermostat to name for warmth. After the furnace runs for a couple of minutes, begin recording CO readings at one-minute intervals for as much as quarter-hour of run time. Seal the take a look at port as soon as your testing is full so it doesn’t leak.

Diagnose the Readings

You have to be affected person and watch the CO readings sample to catch this downside. Should you rush, you’ll miss the development the analyzer reveals. An issue-free furnace ought to have CO readings below 100 ppm which are steady throughout the complete run cycle, as proven under.

Discover the CO readings above are fixed and by no means climb above 20 ppm. It is a signal the furnace is secure and that the stress change received’t journey due to a hidden situation. Now, think about the readings under. They present an unsafe furnace that may doubtless have random stress change journeys.

The CO readings above slowly rise from 20 to 24 ppm throughout furnace operation. These readings recommend the stress change will ultimately journey and lock out the furnace. The furnace can be unsafe as a result of CO readings ought to by no means rise throughout furnace operation!

What’s the Trigger?

So, what may trigger the CO readings to rise slowly? One potential suspect is condensate backing up within the venting system or entice meeting. Condensate slowly accumulates and restricts the venting system and drain, leading to slowly rising CO readings.

Should you’ve ever seen condensate quickly pour out of the condensate drain after the inducer shuts off, you’ve witnessed this downside in motion. The inducer’s suction prevents condensate from draining till the motor shuts off and lets gravity take over. This is identical motion on an air handler drain with no entice within the condensate line.

This situation generally exhibits up throughout prolonged run occasions. The furnace usually doesn’t run lengthy sufficient throughout a mean winter day for extreme condensate manufacturing. That’s why the issue appears to magically repair itself on average days however reappears on the coldest nights.

Widespread Points and Repairs

Typically, you’ll discover a condensate drainage downside is nothing greater than a condensate pump terminated to the outside. It might have frozen and have to be thawed.

Some points are trickier to diagnose. They embrace exhaust pipes which are too quick, too lengthy or have back-to-back elbows appearing as traps. These points can entice condensate and stop draining throughout prolonged furnace operation.

You’ll be able to keep away from many of those issues by following correct venting design and set up procedures. There are extra superior repairs, however they’re past the scope of this text and addressed within the NCI Combustion Efficiency and Carbon Monoxide Security class.

Subsequent Steps

You need to use combustion analyzer measurements for greater than security testing if you already know what to search for. Whereas this text addresses condensing furnaces, the take a look at works for any condensing gear. Strive it and see what you discover.

It’s a wonderful funding to equip your self and your workforce with the take a look at devices and abilities needed so as to add this take a look at to your service procedures. Should you decelerate and take a look at, you may save your self a callback on the coldest evening of the yr and possibly a buyer’s life whilst you’re at it.

David Richardson serves the HVAC trade as Vice President of Coaching for the Nationwide Consolation Institute, Inc. (NCI). NCI focuses on coaching specializing in bettering, measuring, and verifying HVAC and Constructing Efficiency. 

Should you’re an HVAC contractor or technician involved in studying extra about testing and diagnosing with a combustion analyzer, contact David at ncilink.com/ContactMe. NCI’s web site, www.nationalcomfortinstitute.com, is filled with free info that will help you enhance your professionalism and strengthen your organization.