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Air Handling Unit

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I have a residential air handling unit that provides home heat and hot water. In the spring, we noticed that our air conditioning in the house was not functioning properly. An expert adjusted the speed of the Handling unit. Now that it is winter, we have noticed that the home heat works, but the hot water will not work unless the air handling unit is running. If I turn up the thermostat and the unit turns on, the water will go from cold to hot. Do I need to adjust the speed setting of the air handling unit in different seasons? Thank you.
acrepairmississauga0

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  • dbrewer
    dbrewer Member Posts: 9
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    Any help would be much appreciated
  • pecmsg
    pecmsg Member Posts: 4,883
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    A/C requires 1 speed.....Heating another. There are ways of doing this automatically. Get the expert back to fix it!
  • dbrewer
    dbrewer Member Posts: 9
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    I will. do you know if heat or a/c requires being at a higher or lower speed? ie. in winter, should i be reducing or increasing the speed. Are hvac people quite familiar with air handler/hot water systems? I'd never heard of it, but bought a new house with it already installed.
  • pecmsg
    pecmsg Member Posts: 4,883
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    Heating lower speed. A/C higher

    He needs to measure the static pressure and temperature rise / fall
  • dbrewer
    dbrewer Member Posts: 9
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    thank you so much.
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    @dbrewer Can you post some pictures of the system? What make and model is it? Did the hot water work over the summer? If I am reading this correctly you said that you only have hot water when the unit is heating the house. And cold water when the unit is not heating the house?
    pecmsg is right about the speeds, but if that was causing the cold water seems to me like it should be the other way around. Cold water when the unit is heating the house.
  • dbrewer
    dbrewer Member Posts: 9
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    Yes the hot water worked fine. We moved into the home in February 2019. All was fine in the cold weather from feb to May. Then when the a/c kicked in in June, we noticed the house was not cooling(the hot water was fine all through the summer). When the hvac guy adjusted the speed to fix the air, everything worked fine until about 3 weeks ago(I assume this is when more heating was being used in the house). At this point the hot water stopped working, but only when the air handler unit is not running. As soon as we turn up the house thermostat to kick in the heating, the water goes hot. So, it seems that when the home heating isn’t running, the hot water no longer kicks in.
  • pecmsg
    pecmsg Member Posts: 4,883
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    Are you heating and cooling with the water or is it part of a water cooled system?
  • dbrewer
    dbrewer Member Posts: 9
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    It’s an air handler connected to the tankless water heater.
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    It is not the speed of the air handler. There is some other failure. Your tankless unit is not seeing flow unless the pump for the air handler is running. We will need to see pictures of the setup to tell what is going on.
  • dbrewer
    dbrewer Member Posts: 9
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    This is how the settings were during the summer when everything worked fine. Any idea how they should be adjusted. There appears to be 3 adjustments. One for heat, one for cool and one for fan.
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    I suspect there is a check valve stuck open between the air handler and the water heater. it could be in the air handler, or in the pump in the air handler, or in the mess of PEX near the access hatch. It is hard to see what is there. What is likely happening is when you open the hot water tap the water flows backward from the cold line through the air handler and back to the hot lines to the house. A good HVAC guy will be able to find the short circuit.
    It's a new issue. Not the fan speed. Don't touch that fan speed.
  • dbrewer
    dbrewer Member Posts: 9
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    Ok sounds good. I’ll bring the pro back in. I get the impression these aren’t very common systems. It’s hard to find much info online.
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    I wouldn't call it main stream. I have mostly seen them in condos.