Activating gas furnace when heatpump goes into defrost mode


  #1  
Old 12-08-20, 07:07 PM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
Activating gas furnace when heatpump goes into defrost mode

hello,

I got a dual fuel gas boiler(carrier) with an older single stage heat-pump,(12 years old Armstrong)
everything works fine except during defrost mode when cold is blowing inside the house...there are no heating strips or duct heaters installed on the system...
What can I do in order to start the Aux heat (gas furnance) during heat pump defrost mode?
I am guessing the W on the heat pump terminal can be used for that? but where it shoud connect to on the boiler...?

heat pump terminals are: R - C - Y - O - W
boiler/furnace terminals are: W2 - Y1 - Dhum - G - COM(24v) - W/W1 -Y/Y2- R

Thank you
 
  #2  
Old 12-08-20, 10:12 PM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,675
Received 49 Votes on 44 Posts
Need more info as there should already be some connections between systems (G wire) to avoid blowing things up. How does the thermostat connect? Theory is that W from the heat pump comes from the outside unit. May be labeled D there. That then would need to trigger the furnace's W.
 
  #3  
Old 12-09-20, 11:03 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,837
Received 1,476 Votes on 1,364 Posts
Welcome to the forums.

That the first I've heard of a dual fuel system using a boiler.
The boiler will be of little use during a defrost cycle unless you keep your boiler up to full heat...... not cold start.
The defrost cycle requires immediate heat to contradict the cold air that will come out of the ducts. There is going to be a lag between call for boiler and actual usable heat is delivered.
 
  #4  
Old 12-09-20, 04:48 PM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
Thank you for your Reply, this is a great website..

I have read around that it can be done, the lag in between the defrost starting and boiler heat call is not that bad, and I think its worth trying it...

https://iwae.com/resources/videos/ok...isode-110.html

I am using a Nest thermostat but I dont think it has anything to do with the defrost cycle,
I know that the W on heatpump goes to the W on the boiler, but that does not activate heat2 (the gas furnance).
what am I missing?






 
  #5  
Old 12-09-20, 06:49 PM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,675
Received 49 Votes on 44 Posts
Need to see how the systems connect. Some have a dual fuel kit board in the middle so trace the cables to see if you can find the interconnects.
 
  #6  
Old 12-10-20, 05:44 AM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
Thank you for the reply, I have checked and traced the cables, there is nothing in the middle, straight w to w....
usually the 2nd stage cooling kicks in when its really cold outside, usually the whole system works fine. I am just trying to make it work also when the heat pump is in defrost mode.
 
  #7  
Old 12-10-20, 08:09 AM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,675
Received 49 Votes on 44 Posts
We are at a disadvantage of not being on site. Please show how all of the wiring connects including the thermostat(s).
 
  #8  
Old 12-10-20, 08:20 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,837
Received 1,476 Votes on 1,364 Posts
x2

You said boiler and furnace.
Boilers don't have W1 and W2 terminals. They usually have TT terminals.
In your top picture that isn't a boiler control board. Is that an actual gas furnace ?
(A gas furnace blows hot air) OR is that the control board from an air handler ?

My crystal ball is hazy......
I need the model number of that appliance and that control board.
I need the make and model of your boiler.
 
  #9  
Old 12-10-20, 08:52 PM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
You are Right! its called a Condensing gas furnace,

Carrier performance boost 90 gas furnace

model: 58MEC060-F-10112
 
  #10  
Old 12-10-20, 09:01 PM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
  #11  
Old 12-10-20, 09:41 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,837
Received 1,476 Votes on 1,364 Posts
Ok...... furnace. I only see one set of wires on the furnace control board. That means there are going to be splices somewhere. Those look the wires to the thermostat. The white wire from your defrost board should connect into the white wire from the thermostat.

The thermostat must be set up for dual fuel. That means when the stat calls for aux heating it shuts down the heat pump. The furnace cannot be running when the heat pump is in the heating mode. The furnace heat will damage the heat pump. The defrost board can tell the furnace to run because the system is actually in cooling mode during defrost. The furnace can run in cooling mode.

With a high efficiency gas furnace..... why do you need the heat pump ?
Is electricity cheap and gas expensive there ?
 
  #12  
Old 12-11-20, 06:20 AM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
thank you for the info,
yes in my area Elctricity is cheaper than gas...

The nest thermostat is already setup for dual fuel...it tells the gas furnance to commes on when its very cold outside...do you think its still possible to configure it to make the gas furnance comes on in defrost mode?
 
  #13  
Old 12-11-20, 11:04 AM
C
Member
Join Date: Jul 2009
Location: SE Iowa
Posts: 112
Received 4 Votes on 4 Posts
On my Amana heat pump there is a contact on the heat pump side that closes when under defrost mode. This contact feeds a signal back to the gas furnace to signal on the W1 terminal to turn on the gas portion. In my case the gas and defrost work at the same time - the air is only lukewarm out the vents vs. freezing code.
 
  #14  
Old 12-11-20, 11:20 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,837
Received 1,476 Votes on 1,364 Posts
I am guessing the W on the heat pump terminal can be used for that? but where it should connect to on the boiler...
Yes.... a wire from the W terminal on the defrost board needs to connect to the white wire/W1 on the furnace board. There may already be a white wire connected at the defrost board. If yes..... you need to locate the wiring splice area.
 
  #15  
Old 12-11-20, 08:11 PM
M
Member
Thread Starter
Join Date: Dec 2020
Posts: 7
Received 0 Votes on 0 Posts
It works!!
you guys are Awesome!!
There was a wiring splice where the white wire from the defrost board was not connected to w/1

Now the air coming in the house from the registers is not as cold as before!!

Last question: Do you guys think this type of setup is safe for the heat pump compressor long term?




 
  #16  
Old 12-12-20, 07:09 AM
C
Member
Join Date: Jul 2009
Location: SE Iowa
Posts: 112
Received 4 Votes on 4 Posts
I don't see how it will be hard on your compressor. Defrost is another way of saying run the air conditioner in the middle of winter. The hot gas heated air will heat the inside coil up to temps a bit hotter than it would be on a summer day. This is versus taking your warm inside house air and cooling it down, which will take longer to defrost the outside unit. Plus turn around and make it work just as hard to try to heat the inside space back up again once defrost is over.

Side bar - if these smart thermostat companies really want to get serious about saving money (or the environment), in addition to watching outdoor temps on dual fuel systems, monitor time of day and fuel cost. If the user is on time of day usage for electricity, lock out the heat pump at peak times. If the user has solar and production is high, run the heat pump. If natural gas prices have spiked, run the heat pump more and hold the heat pump on longer before reverting to aux/backup heat.
 
  #17  
Old 12-12-20, 08:04 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,837
Received 1,476 Votes on 1,364 Posts
Running the furnace during defrost will help the heat pump defrost faster. Defrost is the system running in A/C mode. That means it's using heated inside air to deice the outside condenser.

What is bad for the heat pump system is the furnace running when the heat pump is in heating mode.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: