Max Caddy Fine Tuning Advice...

[usernametaken]

Here are the basic details of my system: New construction 3500 sq/ft home. 3 zones. 1st floor, 2nd floor, and a bonus room over the garage. Tight MA energy codes followed. We have an LP furnace as well as the Max Caddy. I had the HVAC company do both installs. They also installed electronic system dampers to isolate the two systems for less parasitic loss. The two systems share zone control as well. Bottom line is I flip a switch to go between systems. The switch controls the system dampers and also which system get the call for heat from the three zones and their thermostats. I have a BD installed and my draft is correct. (I needed a bit of make up air as my chimney is quite tall.) So, that's the overall setup and it's running fairly well.

My only issue seems to be with static pressure and that may be just an "is what it is" situation. Static pressure will change based on how many zones call for heat so it can't be dialed in perfectly. That said, on very cold mornings like today (it was 2 outside with over 20 mph winds) all three zones are constantly calling for heat. This is keeping my plenum temps low. The Caddy won't bump up the CFM on it's blower to level 2 until I'm over 140 or so in the plenum and with it this cold and all three zones calling, I'm hovering at 125-130 tops. This means 600 CFM level one on the blower which is not enough for the volume of ducts I have at the current outside temps. Overnight, the house dropped to 65 and the bonus room to under 60. It's working on recovering now that the sun is out but VERY slowly. Most of the time this won't be an issue as last night was extreme cold and wind for my location in Western MA. The system does quite well otherwise. So, any thoughts on things to tweak or will this just be the nature of the beast? I have an extensive sweatshirt collection if need be....LOL

 

[brenndatomu]

Try putting a paper clip on the edge of the intake damper...that will hold it open a crack, not enough to blow all your heat up the chimney, but maybe enough to drive duct temps up some.
You are losing some pretty good BTU's somewhere if a Max can't keep up!

 

[brenndatomu]

And yes, chasing "static pressure" is a snipe hunt...

 

[usernametaken]

The intake damper is always wide open as the controller holds it open when there is a call for heat.

The reason I was concerned about static pressure is because SBI told me that if the air moves through the plenum too quickly, there isn't enough time for heat exchange. It also would keep the plenum at too low of a temp.

 

[brenndatomu]

When I had a Tundra (Caddy basically) the duct temps were highest when the damper was closed and it was cruising along on mainly secondary flames...which doesn't happen so much when the damper is wide open.
"Proper" static pressure seems to be almost impossible to attain with a wood furnace...and since you have zones, it will change everytime a zone damper moves...so you are kinda chasing your tail there. But they are right, the air needs a bit of residence time to pick up heat...maybe try a slightly more restrictive (higher MERV) filter to slow it down a bit?
Do you have the return air ducts hooked up to the Max?

 

[brenndatomu]

all three zones are constantly calling for heat. This is keeping my plenum temps low. The Caddy won't bump up the CFM on it's blower to level 2 until I'm over 140 or so in the plenum and with it this cold and all three zones calling, I'm hovering at 125-130 tops. This means 600 CFM level one on the blower which is not enough for the volume of ducts I have at the current outside temps. Overnight, the house dropped to 65 and the bonus room to under 60

Turn the tstat for the Max down, let the damper shut, see what happens...you will be surprised I think. (especially the first 2-3 hours after loading)(the damper just needs to be open long enough to get a new load burning and up to operating temp)
Heck, I didn't even have the tstat hooked up on the Tundra...many people don't.

 

[usernametaken]

I do have my Caddy tied into the return ducts. I am also surprised that the intake damper is open whenever there is a call for heat rather than based on plenum temp. I wish there was a manual control for it or that the electronic control on it worked differently. In the past when I had wood stove inserts, I too would damper back once the fire was going well and the temp would rise. No can do on the Caddy. If I was to skip the thermostatic control, I would also loose ability to send the heat where needed on an average day. Without zones, my first floor would cook and my bonus room would freeze. I fear that this may just be the way my system runs. I guess everything is a compromise. I am going to jump up on the return filter rating. The Caddy was supplied with a MERV 8 16x20x1" filter that was pretty restrictive after a very short period of time. My HVAC installer is removing the Caddy filter cabinet and installing a proper 20x25x5" cabinet and I'll run a MERV 11 in there to start.

The catch 22 of it is, I need more air volume to fill and supply my long duct runout to the bonus room. However, I need less air volume to get the plenum temp up. Can't have both...

 

[usernametaken]

Just for kicks, I just did a quick experiment. The electronic intake damper defaults to closed when power is removed. So, I removed a wire cap and let it drop. Within 7-10 minutes the plenum temps had dropped 10 degrees and continued to fall when relying on secondary burn only. So, I guess PSG knows what they are doing there...

 

[brenndatomu]

I do have my Caddy tied into the return ducts. I am also surprised that the intake damper is open whenever there is a call for heat rather than based on plenum temp. I wish there was a manual control for it or that the electronic control on it worked differently. In the past when I had wood stove inserts, I too would damper back once the fire was going well and the temp would rise. No can do on the Caddy.

That's exactly why the temp controller was "invented" and put on the Tundra...click on my sig line, it will take you to the very large thread...that is the opening to the rabbit hole. Basically we took a cheap aftermarket programmable controller and used it to overide the call for heat (tstat) by having it monitor the flue pipe temp via thermocouple...it works really well! This can work with your factory controls still in place too. The factory setup of tstat calls for heat, damper opens until tstat is satified is pretty archaic and inefficient.
@Case1030 has put a controller on his Tundra II, which has the factory controls much like your Max has...I think others have done it now too...

 

[brenndatomu]

Just for kicks, I just did a quick experiment. The electronic intake damper defaults to closed when power is removed. So, I removed a wire cap and let it drop. Within 7-10 minutes the plenum temps had dropped 10 degrees and continued to fall when relying on secondary burn only. So, I guess PSG knows what they are doing there...

How long since you reloaded? If its been a while then yeah, you are past the intense secondary burn temps...

 

[brenndatomu]

I'm still surprised that a Max is struggling with a newer 3500 sq ft house...thats a big firebox, something sounds off.
How dry is your wood?

 

[sloeffle]

Just for kicks, I just did a quick experiment. The electronic intake damper defaults to closed when power is removed. So, I removed a wire cap and let it drop. Within 7-10 minutes the plenum temps had dropped 10 degrees and continued to fall when relying on secondary burn only. So, I guess PSG knows what they are doing there...

I have a thermostat hooked to my Caddy, I haven't used it in years. All it does is cause you to burn more wood.

Reload your firebox, set the thermostat to 80F or some temp that the furnace will not be able to achieve in 20 minutes, after 20 minutes, turn the thermostat off / remove the wire cap. As @brenndatomu said you should see the secondaries up top "kick in". Your plenum temps should easily be above 140F at this point. The furnace should then be able to "coast" on secondaries for the next 6 - 8 hours at least with a Max. If the fire goes out, manually open the damper for a few minutes and then put a small nail in the damper. I have to do that with mine.

If the fire goes out with a nail in the damper then my guess is that your wood is too wet. Does the wood sizzle when you put in on top of hot coals ?

 

[usernametaken]

When we cleared our lot, we had our tree guy leave all the hardwood in log length. This years has been split for a year but only stacked and stored inside for a couple months. Wood is between 15-20%. Next year will be better with the addition of my wood shed to extend drying time. I'm surprised the plenum temps aren't higher too. My primary goal for now will be getting that number up. I will definitely read your thread and do some learning there too.

 

[sloeffle]

Wood is between 15-20%.

What percentage do you get on the inside of a piece that was freshly split ?

 

[usernametaken]

The 15-20% is what I'm getting on a fresh split.


One thing to mention about the manual damper control is that I don't have direct access for any propping open. I am running the cold air kit since my home is tight. The cold air kit covers in the intake damper and the control chain runs through the cover.

 

[usernametaken]

To be honest though... I haven't done a ton of re-splitting and moisture testing so my content may be higher than what I saw on a few test splits. I'm betting moisture content is part of the temp issue as well.

As to killing the thermostats, I really can't as I would loose my zoning which is very important to my system.

 

[sloeffle]

To be honest though... I haven't done a ton of re-splitting and moisture testing so my content may be higher than what I saw on a few test splits. I'm betting moisture content is part of the temp issue as well.

As to killing the thermostats, I really can't as I would loose my zoning which is very important to my system.

I don't mean permanently kill the thermostat. Just do what I stated above as a test.

If you are thinking moisture is an issue then maybe get some eco bricks and mix in with your firewood and see how it does.

 

[Wood1Dennis]

.... I wish there was a manual control for it or that the electronic control on it worked differently. In the past when I had wood stove inserts, I too would damper back once the fire was going well and the temp would rise. No can do on the Caddy. ....

Rodney,
I struggled with this on my Caddy too. I do use the wall t-stat to control the damper based on when the house calls for heat. I added a manual control for the damper so that I can adjust how much primary air the furnace gets when the t-stat opens it up. Usually when I have a full load of wood and she is burning good I close the damper down pretty far, it is really open just a slit but that is enough to give it a little more primary air to keep it burning stronger than if I shut down the primary completely. My Caddy dosen't have the cold air kit so it is easy for me to adjust the linkage on the damper with my set-up. Maybe you can add something like it to yours. It is post #2103 in the Everything Drolet Tundra - Heatmax mega-thread.

 

[usernametaken]

All great info guys! I really appreciate it. Again, I'm good most days. Only in extreme cold am I having an issue. I also haven't been able to tweak and fine tune the way I normally would do with a new toy. We sold our house to build this one and lived in our RV as we did so. It was a race to get done and in before we froze in the RV. 7 months from breaking ground to certificate of occupancy.... and this was with me being my own GC. I spent 6 months putting out fires and now I'm finally finding time to get one going... Anyways, I do think my moisture content will improve next season with a new shed and proper drying before bringing it in. I'll also have more time to obsess and research here and find out all the things you all did to get things to your liking. Thanks again...

 

[usernametaken]

PS: I like the idea of the manual damper idea. The pic above illustrates it nicely and I think I can incorporate the same into mine. I also can put a switch inline to the electronic control to my damper but that will only get me full open and full closed. I'll likely do both and let my OCD run wild playing with it until it's right...

 

[usernametaken]

So, I've been doing further experimentation and I just stumbled on what I think is part of my low plenum temps. My barometric damper. I shut it down to it's lowest setting and my temps went up a bit. Still not enough to get me much past 135 in the plenum but better for sure. Then I did an aluminum foil cover. Now I'm up with some decent temps. Pulled about 155 in the plenum this morning and the blower made it to speed 5 of 6. I don't have a Dwyer set up yet but my installer did set the damper initially to the correct draft. I am going to order the Magnehelic that a user posted about here in another thread. Only a few bucks more than the popular fluid filled one that many use. We will see where I am at once it's installed.

 

[brenndatomu]

That's a good way to warp/crack/ruin your new furnace...wait until you get a gauge to go screwing with the draft settings...pulling more than -0.06" (I think that is max draft on the Caddys) is akin to supercharging your furnace...yes it will make more heat, but unless you have a gauge, no way to now how high you are getting...to me its a lot like driving without a speedometer...might be close, might not...are you willing to risk damage?

 

[usernametaken]

I can't damage it running it at the temps it was designed to handle. The plenum over temp warning doesn't even come on until over 200. I'm nowhere near that and haven't even achieved blower speed 6. I see no way to overfire the furnace without having excessive plenum temps... PSG advised me to dial back my baro a while back but I was trying other things first. I guess I should have listened.

 

[brenndatomu]

Its not just about the plenum temps...if your heat exchanger is dirty you can certainly overfire the firebox, and still not have "too high" plenum temps.
If the draft setting didn't matter, then they wouldn't publish the settings, the computer would just adjust the plenum temps as needed.
Just do a little research, see who SBI blamed when all the Tundra furnaces (same firebox design as the Caddys) started cracking...it was the customer..."you overfired it"...and having the draft too high can certainly cause overfiring. Now, as far as I know, SBI did take care of everybody that had a cracked firebox, but it is still a ton of headache to fix/replace. And I can personally vouch for at least one Tundra that was NEVER overfired and still cracked...but kinda getting off topic here.
Personally, if the baro was set correctly by the installer as you say, I wouldn't screw with it until I had a gauge.
But you've been warned, its your furnace, do as you wish with it.

 

[JRHAWK9]

Over-firing is definitely one way to increase your plenum temps! If they still are not not high enough you could always try sticking a leaf blower in your primary air and lettin' er' rip! That may achieve the results you are looking for and could also double as blast furnace just in case you want to start forging your own tools. </tongue firmly planted in cheek>

Like bren said, get your draft in check and leave it there.