Multi-zone HVAC (single furnace) - can one tstat be COOL and one tstat be HEAT

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nh_handyman

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For me - the answer is no - it will greatly shorten the life of the furnace/a-coil.

In any house I have owned that had zones, I have always 'made the switch' at one time. All tstats go to HEAT in the fall and they all go back to COOL in the spring.

Lets say I have a very cold basement and a very warm third floor and I forgot to make the switch:

The basement tstat calls for heat heat

The third floor tstat calls for AC

What is the 12 year old propane furnace going to do in this case?

The zones are controlled by dampers.

Yes - trying to resolve a husband/wife debate.
 

kok328

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Assuming the control board will allow for dual calls, the unit will run both heat and A/C.
 

nh_handyman

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Assuming the control board will allow for dual calls, the unit will run both heat and A/C.

Thanks. This would result in both zones getting 'warmish' air ( I believe).

Given:

- both zones are opened by the control board

- The AC compressor kicks on and will be cooling the pipes in the A-coil

- below that the flames are going to provide heat.

- The blower turns on blowing hot (warm) air over the a-coil ?

The result is very cold pipes with heat blowing over them producing most likely warmish air but I suspect (sure use the word assume) this isn't good for the A-coil?
 

billshack

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Assuming the control board will allow for dual calls, the unit will run both heat and A/C.
I disagree, depends on the system and what is used to control ,
for example some systems are variable volume, some are terminal reheat.
please describe your system and then we can tell you .
 

nh_handyman

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Again - thanks...

Its a Goodman furnace (15 yrs old or so) propane fired - with an A-coil sitting on top for the A/C

Control board is a EWC NCM-300 control_panel.jpg
 

nh_handyman

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Found the answer for my setup:

From: https://www.ewccontrols.com/acrobat/090375a0226.pdf

Opposing System Service Timer A 20 minute delay must expire, or the active zone(s) must satisfy, before the panel will honor a thermostat demand to changeover to the opposite mode of system operation.

With this setup - there will be a 20 minute delay (min) before the system will switch between Heat/Cool operations.
 

billshack

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so the system is a variable volume. if in cooling mode and zone one is happy and zone two is cold then it will close a damper so less air goes into zone two . then yes you can have
 

naslia

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(1) Disconnect from the Shut-Off Valve
(2) Checks the filter
(3) Remove from the Shut-Off Valve
(4) Replacing the Bad filler valve.
 
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