Max Caddy wiring

Hi Jason,

Just a bump so hopefully someone else can chime in. I don't know enough, well, anything remotely related to what you're asking about.

But, can you share any pictures or your install? Or a sketch/layout of your old ductwork and how you tied the new furnace in?

The duct dampers are probably arranged to fail open. That's why they are open in the off condition and close during the operating condition for the off zones. It's a fail safe or fail on for heating.

The oil burner operating condition and the wood burning operating condition sequences may be different, due to the fact that the oil burner can shut down easily and the wood burner may not be able to. I would have to look at the wood burner's ability to modulate draft and burn rate to see what the factory intended.

It's pretty common for me to get a call on a new house someone else wired, to get the heating controls sorted out. Three zone dampers, zone valves, draft inducers, have in fact stumped some professional electricians who otherwise wire houses. This is to say what you are asking for is not simple and I have seen pros smoke the controls or walk away from systems that are not wired correctly. If you thought it was something simple like changing a switch for a dimmer, I would say no. It is a job for a heating controls professional.

Jobs like that are custom control design. If there was a wiring diagram for it, it would come from the factory. What I would expect is each factory part has its own wiring diagram, but there is no single diagram that shows how each is connected to the others. I would have to look at everything and then I would be able to make my own system wiring diagram.

Your post does not indicate your own sequence of operation, when you want the oil to come on and when you want wood. That's where I would start, then the factory wiring diagrams, then the custom control scenario.

I looked at the Caddy installation manual. They recommend or require qualified and experienced technicians for installation and setup. Biggest caveat from a control point of view is the Caddy uses a servo motor to control the air intake damper, apparently on/off for call for heat. That means when there's no call for heat and the damper closes it would be starving the fire for air and making a smoky, incomplete burn and creosote. The manual says to make small hot fires and burn only dry hardwood.

There's two points there the factory is serious about. Using experienced knowledgeable talent for the install and setup and controlling burn rate by the user loading only the necessary fuel quantity at the right time. Overfeeding the fuel relative to the demand may cause the Caddy to make creosote as the combustion air damper closes when the heat call is satisfied. Feeding the right quantity of fuel with the right timing seems to be necessary for successful operation.

Caddy's once up to temperature should not produce creosote once the damper closes. Once the firebox is hot the furnace should maintain clean combustion. The Max caddy modulates the blower based on plenum temps to maintain higher efficiency. The Caddy line of furnace's aren't standard units.

As far as the OP is concerned, I would get a professional out there and look at it. The setup sounds a little in-depth.

laynes69 said:

Caddy's once up to temperature should not produce creosote once the damper closes. Once the firebox is hot the furnace should maintain clean combustion. The Max caddy modulates the blower based on plenum temps to maintain higher efficiency. The Caddy line of furnace's aren't standard units.

As far as the OP is concerned, I would get a professional out there and look at it. The setup sounds a little in-depth.

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I made a couple of assumptions that for me, I would check before proceeding with a plan. I would assume the Caddy maintains a minimum burn rate with the damper closed, that it does not fully starve the fire 100% of combustion air. It appears that the combustion air damper toggles between open and closed, which may be between min and max burn rate, but does not appear to offer an other way to match output to demand.

The duct blower toggles speed to maintain a higher plenum temp, in response to the burn parameter, not in response to demand.

Early in the burn when the fuel is off gassing the volatiles and condensable vapors, that's the time it will least tolerate the damper closing. Later in the burn when the fire is more charcoal, closing the damper will definitely slow it down, probably pretty cleanly assuming Caddy knows what they are doing. It's probably fine under constant load but could have operational problems as the heat call short cycles on and off.

The basic unknown is the overall system efficiency in a practical application. If you have free fuel this is less of a concern. If the fuel costs money, system efficiency matters, and at a certain point system inefficiency or misapplication can be more costly that the alternative solutions or recommendations. That's where hopefully the factory and dealer support is supposed to come in for good effect. There are a lot of variables and parameters to look at. The Max Caddy is the largest of the three sizes.

Jason762 said:

Maybe I made it sound more complicated than it is. The A/C stands alone using it's own blower in the air handler and the existing thermostats that are wired into the Honeywell distribution panel. I don't have any plans on touching that setup.
The wood side of the Max Caddy requires it's own thermostat which I was going to purchase a wireless one and was wondering if anyone had suggestions for which one to purchase.
Lastly the oil burner backup requires a thermostat which would be a set at a lower temp than the wood thermostat, for example the wood thermostat would be set at 70 and the oil at 62 so if the wood can't satisfy the temp that the oil is set at then the oil burner kicks on. My question was there is a wire coming out of the Honeywell control panel connected to the "equipment" port in the panel. This wire used to be hooked to the circulator valve on the old boiler. I assume this is the wire that gets connected to the oil burner on the Max Caddy side. Sound right??? Seems simple enough. Am I on the right track? I believe blower speeds and blower on/off is controlled by settings in the Max Caddy PC unit.

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That's pretty much what I saw in the Caddy installation manual. Their pcb control board has inputs for both externally powered and unpowered dry contact thermostat inputs. So you would have to determine the thermostat type and match.

The lower limit setting for the oil burner is exactly what I was thinking, but I could never assume the customer would live with the swing in temp before the oil comes on. In my opinion, the lower setting is necessary to keep the oil off and maintain load on the wood burning system. It seems the system is designed that way.

It's not clear if you want to run the wood burner with all the zone duct dampers open, or cycling.

I'm starting to agree with what you are proposing though you would have to examine and determine the control sequence you want to happen. If you want the zone duct dampers to cycle with the wood burning operation, the "burner" contacts in the Honeywell controller would tie to the wood input and the new low limit stat would tie to the oil. This is something for the installing contractor to look at as there will be a big difference in duct pressure as zone dampers close but the blower is responding to the burn rate. In this scenario, when calling for oil the duct dampers would already be open and calling for heat.

If you tried the opposite and tied the Honeywell controller to the oil input, these would be tied to your zone stats and set at 70 - 72. If you tried to set these stats lower at 62, the dampers would be closed on wood. There is a way to bypass the dampers, but it's not like hooking up a doorbell. The doorbell either works or it doesn't. With heat, you could freeze something, make steam (overheat the house), or burn your own house down. The installing contractor would make sure that all the safeties are connected and in place.

Jason762 said:

I understand and agree with everything you wrote except this quote below confused me:



Its my understanding that if I use a new thermostat for the wood side set at 72 and tie the Honeywell into the oil input and set the 3 thermostats that tie into the Honeywell at 62, then if the wood burner is keeping the entire house above 62 then all dampers will be open as the 3 thermostats are satisfied and the dampers remain open when there is no call for heat coming from any thermostat tied into the Honeywell.

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It's not obvious and I would ask if this is the factory recommended implementation. What I would expect is that when wood heating, there will be times when there's a call for heat at one of the zone stats, closing the other zones, but they would be satisfied at 62. That's what is known as a failure mode, when the zone dampers are not operating exactly as needed. Yes, I see your point that when all of the zone stats are above 62 the Honeywell controller would be off and the dampers fail open.

I'm not recommending one or the other. It would have to be determined if the wood burner operation does or does not use the zone dampers in the control sequence. There is a control problem where the blower is needed to remove heat from the wood burner, the blower may be tied to the furnace temp in some way, but some dampers could be closed. If the blower needed all of the dampers open because of its rating or requirement, I would most likely arrange a control bypass to make that happen.

Jason. Your way will work fine but you are getting NO zone control, so just lose all the dampers. If you want zone control use the control panel with the wood and the t-stat that came with the caddy to your air handler. MAKE SURE YOU KNOW IF YOUR DAMPERS ARE POWER CLOSED AND SPRING OPEN OR POWER CLOSED AND POWER OPEN. IF THEY ARE POWERED BOTH WAYS AND ONE ZONE IS CALLING AND YOU HAVE A POWER OUTAGE YOU WILL OVERHEAT THE CADDY.

Jason762 said:

Also we plugged in a feed line to one of the trunks downstream of the zone valve. So theoretically that should alleviate my concern of overheating the unit in the case of a power failure when the zone valves are closed, right?

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Valves? I am talking about the dampers of the zone. On the new t-stat wire it to the spot that the honeywell controller hooked into your old furnace. on a power outage you want ALL DAMPERS open.