Drolet heatmax.....what does the rtd control?

nellraq

Member
Nov 6, 2012
82
Coldstream, BC, Canada
I just purchased a drolet heatmax furnace..Will be delivered in a few days.

I have gone through the manual a couple of times. Things look pretty straight forward...EXCEPT when it comes to the control of the auto damper and the control of the fan on/off and fan speed.

re. the fan, there is only one reference to the fan in the manual. It says that the fan will come on when the plenum temp reaches set point. Do you set the setpoint somewhere??? Is it the rtd probe that controls this?
Also, the fan has 4 speeds...what determines the required speed and how is it set?

re. the auto draft via a thermostat. I understand that the tstat opens or closes the draft as required...but what controls this function. Is it the rtd again...does it somehow control the fan and the draft at the same time?

This has me quite confused!! Would appreciate help from an one "in the know!"

Cheers.
 

Case1030

Member
Dec 12, 2017
222
Manitoba
I just purchased a drolet heatmax furnace..Will be delivered in a few days.

I have gone through the manual a couple of times. Things look pretty straight forward...EXCEPT when it comes to the control of the auto damper and the control of the fan on/off and fan speed.

re. the fan, there is only one reference to the fan in the manual. It says that the fan will come on when the plenum temp reaches set point. Do you set the setpoint somewhere??? Is it the rtd probe that controls this?
Also, the fan has 4 speeds...what determines the required speed and how is it set?

re. the auto draft via a thermostat. I understand that the tstat opens or closes the draft as required...but what controls this function. Is it the rtd again...does it somehow control the fan and the draft at the same time?

This has me quite confused!! Would appreciate help from an one "in the know!"

Cheers.
Rtd only controls your fan on/off and fan speed based off your plenum tempurature.

The only time the RTD controls your damper motor is in the event of overfire/over heat... it will close it until the temp is at an adequate level. Also has a mini readout screen on the back to check the plenum temperature.

Their is no simple way to adjust the fan on/off set point. The way my tundra/heatmax came factory is 125f on and (115f or 110f off).

Ultimately your house thermostat controls your damper.

EDIT- Variable 4 speed fan will increase with your plenum temp. Most your furnace will likely use is speed 2. Make sure to follow instructions for thermostat placement. Prevents the damper from staying open for extended periods.

Simple mods can increase efficiency of the furnace but I'd see how it works before playing around.
 

nellraq

Member
Nov 6, 2012
82
Coldstream, BC, Canada
Thanks for your quick response Case.

So the tstat must activate a motor or something to open and close the damper. Got it...I think!

Haven't figured out how I'm going to do the ductwork yet...hopefully will be able to find an experienced person to help with that.

Temp controller load 'n go...hmmm, already interested in that mod!! but you are right..i'll get things going and get the bugs out before I quiz you on that!!

Cheers. and thanks a lot!
 

KC Matt

Burning Hunk
Oct 29, 2016
126
Kansas City
In my opinion, a wood furnace doesn't lend itself to a standard house thermometer. A wood furnace isn't an "on demand" appliance; it's a constant heat with a limited fuel supply. If you light the firebox and the house is below your set temp, the thermostat will hold the damper open until your fuel is nearly gone and you will have lost the opportunity to capture the energy of the offgasses which is the advantage a modern furnace has over an old smoke dragon. By the time you reach the set point, you'll be down to coals and if you reload you'll overshoot your set point. In very cold weather, you'll build up coals to a point the furnace won't provide enough heat to reach your desired temp.

Instead, I suggest buying a separate digital temperature controller and installing the probe in the duct work or on the heat exchanger if the probe can handle the temp. This allows you to maximize the available heat in your fuel and to adjust the house temp you set the supply temp up or down. Mine is a Johnson Controls/Penn 421 box which I recommend but others have used the generic $20 units.

I also recommend a second 421 box to control your fan on/off because the factory switch comes on long after it should. With a digital controller you can have it come on and off where it works best for you. Mine came on with a supply temp of 150-160F after the fuel was half gone and now it comes on at 98 and shuts off at 70.

I've had my Tundra1 running for 3 full winters and wouldn't trade my system for anything but a Kuuma.
 

KC Matt

Burning Hunk
Oct 29, 2016
126
Kansas City
Wait, doesn't a standard home thermostat output 24vac down the "W" wire to activate the furnace? If so you'll need to verify that's what you need to open the damper. With the Tundra1 you just connect the two posts and if you supply 24vac you nuke the damper control motor and the transformer.
 

brenndatomu

Minister of Fire
Aug 21, 2013
4,377
NE Ohio
Wait, doesn't a standard home thermostat output 24vac down the "W" wire to activate the furnace?
Some might...most are just a thermostatic switch that puts the 24V from the furnace back down to the damper motor...pretty sure the T2 is the same way
 

Case1030

Member
Dec 12, 2017
222
Manitoba
The whole idea drolet is counting on is proper placement of a thermostat so the damper will open and close as the house gradually warms up. If the thermostat is to close (Hot air ducts) it will open and close to often, to far away it stays open nearly the whole burn.

It isn't the most efficient way but it's still better than a manual damper.

The caddys are designed the same way as the tundra. Many folks use the thermostat and don't bother with a temp controler. It's all about getting the most out of the furnace.
 
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KC Matt

Burning Hunk
Oct 29, 2016
126
Kansas City
Some might...most are just a thermostatic switch that puts the 24V from the furnace back down to the damper motor...pretty sure the T2 is the same way
EDIT: I see now, the thermostat is closing a circuit which would wouldn't blow up the damper motor. It's still a poor solution.

I found a Penn/Johnson 421 for $65 online. That's a no-brainer. These things are used to control the cooling units in massive warehouses that house millions of dollars in perishable inventory. That's the kind of dependability I want for an appliance that controls a fire burning within my house.
 
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KC Matt

Burning Hunk
Oct 29, 2016
126
Kansas City
The whole idea drolet is counting on is proper placement of a thermostat so the damper will open and close as the house gradually warms up. If the thermostat is to close (Hot air ducts) it will open and close to often, to far away it stays open nearly the whole burn.

It isn't the most efficient way but it's still better than a manual damper.

The caddys are designed the same way as the tundra. Many folks use the thermostat and don't bother with a temp controler. It's all about getting the most out of the furnace.
Gotcha! Yeah getting the most out of your furnace and more importantly your fuel is the name of the game. That's why a digital controller is a must in my view.