Integrating dampers on parallel furnace setup.

[JRHAWK9]

I like RIBs.....it's what I used.
(broken link removed to https://www.functionaldevices.com/products/building-automation/relays/)

 

[woodey]

That's what was used on mine.^^^^

 

[andym]

I'll check out those links. Thanks!
Received my gravity damper today. It came wrapped in about 6 yards of bubble wrap. They literally could have shipped ten dampers in that box! Must only have one size of box? I wasn't real happy with how it was built (not nearly enough airflow) so I remodeled it some to increase airflow. Installed and tested it. Works super great. Now on to the relays.....

 

[brenndatomu]

I like RIBs.....it's what I used.
(broken link removed to https://www.functionaldevices.com/products/building-automation/relays/)

Yeah, those work good if you have the room for them (should here) and they are nice for people relatively inexperienced in wiring since they come with pigtails wired on already...little spendy compared to plain ole "ice cube" relays, but hey...

 

[JRHAWK9]

I used to have the cube type but my HVAC buddy said they have a high failure rate (at least the ones I was using). I had one that was starting to fail too. At his work they use all RIB's, so I switched them out.

 

[brenndatomu]

I used to have the cube type but my HVAC buddy said they have a high failure rate (at least the ones I was using). I had one that was starting to fail too. At his work they use all RIB's, so I switched them out.

I've personally never had issues with them, but try to stick with major brands though too...and plenty of ampacity for the job...don't like running close to rated load.

 

[JRHAWK9]

I've personally never had issues with them, but try to stick with major brands though too...and plenty of ampacity for the job...don't like running close to rated load.

Ones similar to these is what I had.

90-380 - White Rodgers 90-380 - Fan Relay, Type 184, 24 VAC Coil, 50/60 Hz, SPNO/SPNC. Coil Data: 77 Ohms DC Resistance, 125 mA

White Rodgers 90-380 - Fan Relay, Type 184, 24 VAC Coil, 50/60 Hz, SPNO/SPNC. Coil Data: 77 Ohms DC Resistance, 125 mA - Heavy-Duty General Purpose Relay Operates in Any Position<br /><br /><b>Features</b><br /><ul><li>Compact, totally enclosed design<li>For heating and cooling applications and...

www.supplyhouse.com

 

[brenndatomu]

Ones similar to these is what I had.

90-380 - White Rodgers 90-380 - Fan Relay, Type 184, 24 VAC Coil, 50/60 Hz, SPNO/SPNC. Coil Data: 77 Ohms DC Resistance, 125 mA

White Rodgers 90-380 - Fan Relay, Type 184, 24 VAC Coil, 50/60 Hz, SPNO/SPNC. Coil Data: 77 Ohms DC Resistance, 125 mA - Heavy-Duty General Purpose Relay Operates in Any Position<br /><br /><b>Features</b><br /><ul><li>Compact, totally enclosed design<li>For heating and cooling applications and...

www.supplyhouse.com

Oh, those...yeah, I have had some issues with that particular style too...try to upgrade when at all possible.

 

[andym]

Thought I would finally post the results of my tinkering since the season is nearing the end. I ended up getting 4 of the cube relays mentioned above. I tied into each of the 4 blower output wires to allow each one to control it's own relay. The 24v going to the motorized damper is fed through the normally closed contacts of each relay. That means if any of the 4 relays are energized (wood furnace blower running) the motorized damper does not operate (remains open). At any time when the wood furnace blower is off, the LP/AC blower can power the damper closed as needed.
There have been several times this past month when both furnaces were running. I could tell the wood furnace did not cool off as quick in that scenario. Also the airflow out of registers was more noisy. I wouldn't want it to a operate like that all the time, but it only really happened when the real feel approached 0° F or lower.
One interesting thing I discovered along the way that others may want to note: the phantom voltage that I mentioned earlier in the thread did not dissappear when connected to a relay. What I found is that no matter what blower speed is in use all 4 relays are being energized. So all I would have needed was one relay wired to any of the 4 speeds. I haven't changed it yet, but will at some point.
Overall I really like this setup. Thanks to those who offered their help!

 

[JRHAWK9]

It's nice knowing both can play nice if needed. Just this week I was outside in the garage after dinner and the Kuuma was not running at all during the day, so the house was cooling down...I think it was a whole 68°. I lit a fire in the Kuuma and went back outside. I come in and someone ( ) was cold and being impatient and turned the LP furnace on and set it to 75°. So the Kuuma with a fire I just started and the LP furnace were dancing together while I was outside and didn't even know it. This is one situation where I wanted to make sure they could....if someone flipped the heat on with a fire in the firebox. Seeing the Kuuma was just getting started, if the blower would have kept being speed controlled while the LP blower is running, the LP furnace would have ended up backfeeding the Kuuma.....due to how slow the Kuuma's blower would have been running. I know this because it happened with the prior setup I had before being speed controlled. I soon realized this shortly after adding the speed controller and had to add another relay in order to change that. So now when the LP blower runs, the Kuuma's blower switches from being speed controlled via the high speed tap to straight up on the low speed tap. I also have the LP blower using the low speed tap when being used for heat.