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So I had some problem with my gas furnace and a technician came by to install a new one but it doesn't have the same rating and only has one tube instead of two. He assures me it's fine but I thought all furnace repairs had to be made with OEM parts? Can anyone let me know if this is safe and if it will affect the life of my furnace?

The furnace is a Lennox ML195 Single stage 95% efficiency furnace. He replaced the whole pressure switch but the new one has only one port whereas the old one has two, so now there is a hose that is unconnected on one end. Also the old pressure switch has a rating of 0.90 PF and the new one says 0.27" WC is that the same?

Tester101
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wjcmogui
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The documentation for your furnace, calls for a switch rated at 0.90" wc. Using a switch with a lower rating, means that the switch may be closing without the proper inducer air flow.

If you called the tech out because the furnace was not working, you may have a problem that was preventing the switch from closing. By putting in a different switch, the tech might just be ignoring a big problem.

There are three main reasons that a combustion air pressure switch would not close.

  1. Obstruction/restriction of the air intake.
  2. Obstruction/restriction of exhaust.
  3. Backed up condensate.

Pressure switches can go bad. However, they are more often than not an indicator of a problem, not the problem itself.

I'd call the company, tell them your concern, and ask them to send out a different tech to fix the problem.

It's possible that this is a legit remedy, since you say the new switch is only connected to a single port on the unit. This means that, instead of reading the pressure differential across the inducer. The new switch is reading the difference between the pressure inside the unit, and atmospheric pressure. I was not able to find any documentation on this type of substitution from Lennox, so I'm not sure if it's an approved fix or not.

Tester101
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I know this is an older post: As a Lennox dealer for 40 years, I've installed many of the same EL19 models. The .90 pressure switch is no longer used in this model furnace as a replacement. Lennox provides two choices a .80 or a .65 switch. Using one of the two tubes is not the end of the world, but the second tube is used to measure the suction pressure on the primary heat exchanger (heat exchanger where the flue gases condense out water vapor). If this tube is left off and in the very rare case the this heat exchanger became clogged or the drain leaving was clogged the pressure switch would signal a warning. For a short time using a one port pressure switch is ok, but only until an OEM or close matching aftermarket part is found. Your technician does not fully understand the purpose of the pressure switch. One man companies are usually a better value (charge less because they have much lower advertising and overhead costs), but it's always best for the consumer to ask "What purpose does the other hose port provide?" or similar questions, if the answer makes no sense then it's best to press for an OEM part.

Dennis Treacy
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Under proper conditions the burner flames could roll out causing a fire and damage to your furnace should the flue become partially clogged. Engineers spent a lot of time and testing to determine the proper switch for the furnace. It is fine to use after market parts but they must have the same rating and design characteristics.

user76730
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