I'm looking to buy an apartment in Chicago, IL, and the building has told me they are on a four pipe HVAC system. When I asked to test the heat, they said they are using all four pipes for cooling because it's the summer. My understanding was that a four pipe system was always two pipes for chilled and two pipes for heated. Am I wrong? I'm very suspicious of this building.

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    Welcome! I always learn something here. I Have never come across a HVAC system labeled by the pipes. What pipes are they referring to?
    – Gil
    Jul 6, 2022 at 14:56
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    "I'm very suspicious of this building." Probably a good reason to just move on. I know the housing market has been crazy the last 2 years, but it's starting to slow down. I'm just south of you in the Indianapolis area, and houses that would have sold in days have been sitting on the market for 2+ months. You'll find another one that you won't feel suspicious about.
    – FreeMan
    Jul 6, 2022 at 17:18
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    Hardly inconceivable for it to be set up this way, but just pass if the management gives you bad vibes and you have not yet committed to be stuck with management that gives you bad vibes.
    – Ecnerwal
    Jul 6, 2022 at 18:01
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    touch the 4 pipes and compare the temperature
    – Traveler
    Jul 6, 2022 at 18:47

1 Answer 1


Most 4 pipe systems that I've seen do have 2 pipes for chilled water for AC and two pipes for hot water for heat. If the hot water system is only for heat and not for supplying hot water to the units, the boiler will usually be shut down in the summer so testing the heat would be difficult. This is something that might not be totally understood by the sales people. Bottom line, if you're suspicious of these people, don't do business with them until you're satisfied with all your concerns.

  • Thanks, this is very helpful. The feedback about trust is valuable, too, but I know myself and I can overreact on these things, so I thought it best to check. Quick follow-up if you have the time: why have a four pipe systems if you're going to shut off the hot water pipes for the summer? Jul 7, 2022 at 17:13
  • @Callus-ReinstateMonica Excellent point. A main advantage of a four pipe system is the availability of heat and cool at the same time without having to do a lot of valve opening and closing since there are different coils for each. Shutting down the heating system in the summer or the cooling system in the winter eliminates that advantage. they probably decided afterwards it was cheaper to do that.
    – JACK
    Jul 7, 2022 at 17:47

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