Napoleon HMF200 major design flaw - want feedback!

[Caydel]

Hello everyone!

I have a Continental CHMF200 wood furnace (A Napoleon HMF200 with blue paint instead of red) that I had installed at the end of March. I want to say up front that I love it for the most part - it burns hot, efficiently, and does an amazing job of heating my house. However, I believe there is a major defect with it, and I want to get some second thought on it before I chase it any further.

Design-wise, this furnace is basically a standard EPA firebox. However, the primary air supply is controlled by the upstairs thermostat - if the temperature is lower than the thermostat setting, the air supply is opened. If the room is warm enough, the primary air supply is closed. It can be overridden to open the primary air intake by manually locking the air control open (so the thermostat can't close it). You *can't* override it to close down the primary air intake if it wants to be open. The primary air is either 100% open or closed, there is no in-between state.

In the plenum above the heat exchange tubes, there is a thermosensor that trips at 250F and triggers the furnace blower to come on.

Now, in the manual, it specifies the following regarding the motor that opens the primary air control:

The control circuitry will energize the motor if it detects the room thermostat is calling for heat and the high limit sensor in the supply plenum has not been surpassed (greater than 250F (121C)). The primary air shutter will be fully opened and will remain so unless the room temperature has been satisfied or too much heat is detected in the plenum.​

The bold sections imply that when the temp sensor in the plenum is tripped, the primary air supply should be closed down, and remain closed as long as the plenum temperature is above 250F.

To me, this makes perfect sense. As far as I am aware, this is how every non-catalytic EPA stove in the world operates - once the firebox is up to temp, you close down the primary air supply to trigger / improve the efficient secondary burn.

However, the unit as delivered does not do this, nor does a similar unit owned by my brother-in-law. There is no interconnect between the high limit switch in the plenum and the primary air control. This means that as long as the room thermostat is calling for more heat, the primary air control will remain wide open regardless of firebox temps.

This has led to some scary chimney temps, and caused me to go through a pile of wood before I realised what was happening.

I have been working around this as follows -

1. I set the room thermostat to 10 degrees Celcius (50F) so that the primary air intake wants to be closed and leave it there 24/7.
2. I override / lock the primary air intake open when I start the fire.
3. When the firebox reaches operating temperature, I unlock the primary air control so it can close as per the thermostat signal. This triggers a wonderful secondary combustion burn.

By operating the stove this way (basically like any other EPA stove I've owned), I've nearly cut my wood usage in half and no longer see super high chimney temps. I get beautiful secondary burn, and terrific heat output.

In my opinion, the furnace as delivered has a major and potentially dangerous defect. Furthermore, the automatic draft control is one of the features I bought this unit for - I actually read the manual before ordering it.

Accordingly, I followed up with my HVAC contractor, who in turn followed up with Napoleon with me on the line. The tech support person we spoke with confirmed that the behaviour we saw (primary air control operating *only* via thermostat) was the intended behaviour as there is no interconnection between the high limit switch in the primary air control. I wasn't satisfied, but I didn't have the manual in hand.

Today, I dug out the manual and found the section quoted above. I again spoke with their tech support (the same person as the first time around), this time with the manual page number handy. They reviewed the manual, and agreed with me that the manual indeed said the above, but that wasn't how the unit was actually built as there is no interconnect between the limit switch and the primary air control.

They are suggesting that I merely have a draft problem and will not go any further until I have my draft level checked.

I'm going to have that done, but I've been burning EPA wood stoves for over 10 years now. I understand how they work and how to efficiently and safely burn wood. I don't believe this is a draft issue - I think the design for this furnace was originally to have an interconnect between the high limit switch and the primary air control as per the manual, but it got deleted at some point.

I can't accept the only time we can get a good secondary burn by closing the primary air control is when the house is *already* at temperature. I have a large house, and it can take a full burn cycle to raise the temperature by 5 degrees on a cold winter day, or two cycles if the primary draft remains open the whole time (as is the apparent design).

I'd love some feedback on this. While I am managing it for myself with the workaround process I've described above, I think this is potentially a dangerous unit if allowed to manage it's own air control, in addition to being remarkably inefficient.

I don't want to be 'that guy', but I'm concerned that this is a dangerous issue and I want it resolved. I don't want someone else to overfire their furnace and chimney because they trusted the design of the primary air control.

To end on a positive note - I am supremely happy with the performance of this unit as far as efficiency and quality of burn goes, as long as I manage it the way I've described above. I just wish it worked the way the manual specifies without me having to use a workaround.

Edit: Add the manual page

 

[3fordasho]

Do you have the factory wiring diagram ? If so post it. The high limit if tripped should shut the primary air no matter what, at least that is how SBI does it in the Drolet Tundra.

 

[Caydel]

Do you have the factory wiring diagram ? If so post it. The high limit if tripped should shut the primary air no matter what, at least that is how SBI does it in the Drolet Tundra.

First off, thanks for taking the time to read my 'wall-o-text'. Once I posted, I realised it was longer than I had thought, and figured nobody would take the time.

I'm uploading three files. The first is the main control wiring, which I can confirm is done correctly (ie, not an installation error).

There's also two diagrams of the main control harness. I've traced them as best I can, but from what I can see, unless the connection with the limit switch is inside the main terminal block, I don't think there is one. Perhaps you can understand it better than I can.


Edit: So the room thermostat and damper motor are in series, and attach to wires 10 and 11 on the top terminal.

Wires 10 and 11 connect directly to the interlock relay. The other side of the relay runs to wires 3,4,5 & 6 on the top terminal. 3 & 4 are not connected to anything. 5&6 connect to the gas furnace thermostat and control board. Apparently this is the interlock system... however, in the manual it says:

Note the interlocks in the control system will force the secondary heat source to shut down if the temperature in the supply plenum of the wood furnace exceeds the set value of the 'High Limit' switch (250F)(121C)
​

Again, this system is supposed to be impacted by the high limit switch. Usually, this works.

 

[3fordasho]

First off, thanks for taking the time to read my 'wall-o-text'. Once I posted, I realised it was longer than I had thought, and figured nobody would take the time.

I'm uploading three files. The first is the main control wiring, which I can confirm is done correctly (ie, not an installation error).

There's also two diagrams of the main control harness. I've traced them as best I can, but from what I can see, unless the connection with the limit switch is inside the main terminal block, I don't think there is one. Perhaps you can understand it better than I can.
View attachment 222001 View attachment 222002 View attachment 222003

Edit: So the room thermostat and damper motor are in series, and attach to wires 10 and 11 on the top terminal.

Wires 10 and 11 connect directly to the interlock relay. The other side of the relay runs to wires 3,4,5 & 6 on the top terminal. 3 & 4 are not connected to anything. 5&6 connect to the gas furnace thermostat and control board. Apparently this is the interlock system... however, in the manual it says:

Note the interlocks in the control system will force the secondary heat source to shut down if the temperature in the supply plenum of the wood furnace exceeds the set value of the 'High Limit' switch (250F)(121C)
​

Again, this system is supposed to be impacted by the high limit switch. Usually, this works.

I can't really tell what is going on by those diagrams, they are more wire routing diagrams then complete schematics. Missing info like relay and limit switch contact arrangements.

The air damper motor functions the same as in my Drolet Tundra - Thermostat calling for heat= open damper, thermostat satisified = closed damper. As you have found you want the damper closed for long burns and efficient operation. The only time I have an open damper is for start ups and reloads to get the firebox up to operating temp. I accomplish this not with the thermostat but with a wind up timer switch 0-60mn. This timer switch is wired in parallel with the thermostat. In my case I leave the thermostat in the OFF position at all times.

As far as the limit switch, are you sure things have got hot enough to actually trip it? Regardless it needs to function properly.

I've only tripped the high limit on my Tundra once, when the blower failed to run. The high limit on the Tundra is something like 180F, with yours at 250F it will take quite a bit to hit that, probably only possible if the blower does not run.

 

[brenndatomu]

Unfortunately those attachments get too blurry to read when blown up to readable size...at least on my laptop...maybe a smart phone would do better?
A couple observations...I agree that the high limit switch (hence the name) should close the damper! It does so on every wood furnace I've ever owned. The other thing is that 250* plenum temp is awful high! Is it adjustable?
No way would I want my ducts over 200*...wood (house framing) can spontaneously combust as low as 190* if it goes through pyrolysis long enough...and even many duct insulations are only good to 200*.
Just order a Dwyer Mark II model 25 manometer and check your own draft...all the time...just leave it hooked up. They can be bought for $30-40 on fleabay and others.
Your finding of the thermostat holding the damper open way too long for good efficiency is common among almost all wood furnaces that are T-stat capable. That's why a bunch of us have installed DIY temp controllers on our furnaces.
It can be read about in the Everything Tundra thread...link at the bottom of my post. A glossary of the thread is permanently at the top of the listings in the boiler room forum.

 

[Caydel]

As far as the limit switch, are sure things have got hot enough to actually trip it? Regardless it needs to function properly.

Yes - the limit switch trips with an audible 'click'. When it trips, the blower fan turns on as it should. As far as I can tell, the switch is tripping on and off at the temperatures it's supposed to.

Also, this is supposed to disengage the backup gas furnace, which I believe it usually does. I've never had the gas furnace kick in after the limit switch has engaged. However, if the backup furnace is currently running, it doesn't necessarily shut off when the limit switch is tripped - it seems to continue to run until the room thermostat is happy.

 

[3fordasho]

Yes - the limit switch trips with an audible 'click'. When it trips, the blower fan turns on as it should. As far as I can tell, the switch is tripping on and off at the temperatures it's supposed to.

Also, this is supposed to disengage the backup gas furnace, which I believe it usually does. I've never had the gas furnace kick in after the limit switch has engaged. However, if the backup furnace is currently running, it doesn't necessarily shut off when the limit switch is tripped - it seems to continue to run until the room thermostat is happy.

Ok, sounds like a combination fan and high limit switch, that is why there are more than 2 wires going to it, what you are hearing close is the fan switch, not the high limit switch.

 

[Caydel]

Unfortunately those attachments get too blurry to read when blown up to readable size...at least on my laptop...maybe a smart phone would do better?

Sorry - they look good when I blow them up on my desktop, but I suspect the different screen size would make it 'zoom' differently!

A couple observations...I agree that the high limit switch (hence the name) should close the damper! It does so on every wood furnace I've ever owned. The other thing is that 250* plenum temp is awful high! Is it adjustable?
No way would I want my ducts over 200*...wood (house framing) can spontaneously combust as low as 190* if it goes through pyrolysis long enough...and even many duct insulations are only good to 200*.

I can't adjust it without violating the warranty. If it comes to that, maybe I would consider lowering it, but I would rather try to get this solved the right way first. However, to note - the temp switch is located low in the plenum - just above the heat exchanges. However, hot air rises - the top of the plenum and the ducts connected up high heat up first presumably through convection. I can feel the heat come down lower and lower in the plenum until it gets to level of the switch. I would guess the top of the plenum gets above 250F. However, there's decent spacing from combustibles, and the connected ducts cool down quickly as you travel away from the plenum (prior to the blower engaging).

Just order a Dwyer Mark II model 25 manometer and check your own draft...all the time...just leave it hooked up. They can be bought for $30-40 on fleabay and others.

Your finding of the thermostat holding the damper open way too long for good efficiency is common among almost all wood furnaces that are T-stat capable. That's why a bunch of us have installed DIY temp controllers on our furnaces.
It can be read about in the Everything Tundra thread...link at the bottom of my post. A glossary of the thread is permanently at the top of the listings in the boiler room forum.

Thanks! I'll look into those recommendations. I just don't like that I may have to go down that route to have a 'safe' furnace.

 

[NaturalCauses]

Ok, sounds like a combination fan and high limit switch, that is why there are more than 2 wires going to it, what you are hearing close is the fan switch, not the high limit switch.

I was just going to say this, it's how my Caddy is set up as well.

Sent from my Pixel using Tapatalk

 

[Caydel]

Ok, sounds like a combination fan and high limit switch, that is why there are more than 2 wires going to it, what you are hearing close is the fan switch, not the high limit switch.

Hmm, ok, that may be... However, I've never seen the primary air control close regardless of how hot the firebox gets (nor the exhaust stack). Plus, the support person I talked to maintains that the primary air control is *only* controlled by the thermostat, which lines up with what I've observed.

I don't think it's just me not letting it get hot enough.

 

[3fordasho]

Ok, sounds like a combination fan and high limit switch, that is why there are more than 2 wires going to it, what you are hearing close is the fan switch, not the high limit switch.

Hmm, ok, that may be... However, I've never seen the primary air control close regardless of how hot the firebox gets (nor the exhaust stack). Plus, the support person I talked to maintains that the primary air control is *only* controlled by the thermostat, which lines up with what I've observed.

I don't think it's just me not letting it get hot enough.

The high limit may kill power to the 24vac transformer. That is how it is done on the Tundra. I was hoping the wiring diagram would show me that but not enough info there.

The Tundra is set up with two different snap switches, a 120F that turns on the blower fan, and a 180F snap limit switch that kills 120VAC to the 24vac transformer that powers the air damper motor. Any way it takes quite a bit to trip the 180f switch on the tundra, and if yours is 250f it will take sometime with no blower running to trip that depending on where that switch is actually located on the furnace.

 

[brenndatomu]

I can't adjust it without violating the warranty

Really? The high limit temp maybe...but the blower on/off temp should be fully adjustable if it is a combo switch. This would be a common Honeywell switch

I just don't like that I may have to go down that route to have a 'safe' furnace.

As far as checking the draft...that is a requirement on many/most solid fuel furnaces.
Do you have a damper in the flue pipe...manual or barometric?

However, to note - the temp switch is located low in the plenum - just above the heat exchanges.

That's kinda strange...they are usually high in the plenum...Kuuma even tells you to move them there if you are having issues.

 

[Caydel]

The high limit may kill power to the 24vac transformer. That is how it is done on the Tundra. I was hoping the wiring diagram would show me that but not enough info there.

The Tundra is set up with two different snap switches, a 120F that turns on the blower fan, and a 180F snap limit switch that kills 120VAC to the 24vac transformer that powers the air damper motor. Any way it takes quite a bit to trip the 180f switch on the tundra, and if yours is 250f it will take sometime with no blower running to trip that depending on where that switch is actually located on the furnace.

Really? The high limit temp maybe...but the blower on/off temp should be fully adjustable if it is a combo switch. This would be a common Honeywell switch View attachment 222026

As far as checking the draft...that is a requirement on many/most solid fuel furnaces.
Do you have a damper in the flue pipe...manual or barometric?

That's kinda strange...they are usually high in the plenum...Kuuma even tells you to move them there if you are having issues.

Ok, so the switch on mine is a White-Rodgers. The manual is here: (broken link removed to http://www.royallfurnace.com/support/components/fan-limit-switch.pdf)

From what I can see, the fan on is set at 150. The fan off is set at 100. The limit is set at 250. So yes, I am likely seeing the fan switch triggering, but not ever hitting the limit. I'm tempted to pull it, get it to 250, and seeing if it closes the primary air control like it's supposed to in the documentation.

As for height - the install manual specifies 6 1/2" from the base of the plenum. I just measured, and the switch is 28" from the top of the plenum so... by the time the fan kicks on, there is a lot of hot air built up already!

So, it's reasonable perhaps that with the fan running, the plenum never gets up to 250 degrees, and therefore the limit is never hit and the primary control never closes.

Ok, good - at least I think now I understand what's going on.

 

[JRHAWK9]

Here's a link to the manual.....
https://napoleonproducts.com/downloads/hvac/manuals/updated/W415-1504.pdf


OK, I just want to vent a little about manufacturers websites and what they claim and want people to believe. I know the OP is from Canada.

I found this on their website:

As of November's EPA list of certified warm air furnaces, the HMF200 was not even on it. So, as of November 2017, it has not even passed the first phase of the certification, which is required to be able to be currently sold in the US. I also could not find ANY EPA data on their site what-so-ever. Their manual has not been updated per EPA requirements either.

Link to the list of EPA certified warm air furnaces: https://www.epa.gov/sites/production/files/2017-04/usepa-certified-forced-air-furnace-list.xlsx

Maybe it has passed phase 1 and will be on the next updated EPA list. Who knows, but it's obvious the company either doesn't have any real test data or they are trying to hide something.

 

[Caydel]

As of November's EPA list of certified warm air furnaces, the HMF200 was not even on it. So, as of November 2017, it has not even passed the first phase of the certification, which is required to be able to be currently sold in the US. I also could not find ANY EPA data on their site what-so-ever. Their manual has not been updated per EPA requirements either.

Link to the list of EPA certified warm air furnaces: https://www.epa.gov/sites/production/files/2017-04/usepa-certified-forced-air-furnace-list.xlsx

Maybe it has passed phase 1 and will be on the next updated EPA list. Who knows, but it's obvious the company either doesn't have any real test data or they are trying to hide something.

Thanks for the manual link - that's what I've been screenshotting for others! I should have thought to link it myself.

You know - I just assumed it was EPA certified. I mean, it's been so long since I saw a wood appliance for sale that *wasn't*. That said, as I'm finding, it doesn't actually burn with high efficiency 'out of the box' without manual intervention!

 

[maple1]

I think while I was rounding up a Dwyer (yes, you really should have one - you can use it to get your duct pressures right also), I would get a decent temp measuring tool too - a good IR gun maybe (keep in mind they don't measure shiny surfaces well - a blotch of flat black spray paint is needed first). You would have a better handle on things working 'right' or not. And that 250 limit sounds kind of sketchy to me, that's pretty hot.

 

[Caydel]

Another update:

So, I bent a paper clip. If I jump the fan terminals on the fan / limit switch, the fan kicks on as you would expect.

However, if I jump the Limit switch portion, nothing happens - at least, the air damper motor does not de-energise. At this point, it doesn't look like it's a case of the limit switch not being hit. It may not be getting hit, but even if it does, it won't shut down the damper motor. It *may* trip the interlock however - I'll need to confirm that but I expect it's working.

 

[3fordasho]

Another update:

So, I bent a paper clip. If I jump the fan terminals on the fan / limit switch, the fan kicks on as you would expect.

However, if I jump the Limit switch portion, nothing happens - at least, the air damper motor does not de-energise. At this point, it doesn't look like it's a case of the limit switch not being hit. It may not be getting hit, but even if it does, it won't shut down the damper motor. It *may* trip the interlock however - I'll need to confirm that but I expect it's working.

Black #9 on the limit switch is 110Vac hot. I will assume the limit switch opens when it hits 250F. What is blue #5 feeding? I think Blue # 5 looses power when the limit it hit. (again minor assumption on my part).

Page 54 in manual, diagram 7.4.3 did you see the note about "Move wire #5 to terminal #6 for "add on", "stand alone" wood furnace and wood /electric configurations" ?

Lots of diagrams and different combinations to sort through there and real tough to sort out from behind the keyboard, better to be there with a multimeter.

 

[Caydel]

Black #9 on the limit switch is 110Vac hot. I will assume the limit switch opens when it hits 250F. What is blue #5 feeding? I think Blue # 5 looses power when the limit it hit. (again minor assumption on my part).

Ah, you would be correct. I was thinking the limit switch closes when that temp is hit. It actually opens.

Page 54 in manual, diagram 7.4.3 did you see the note about "Move wire #5 to terminal #6 for "add on", "stand alone" wood furnace and wood /electric configurations" ?

In my case, 7.4.2 would be the correct layout as I have the Continental gas furnace, but yes, wire #5 was moved to #6.

Lots of diagrams and different combinations to sort through there and real tough to sort out from behind the keyboard, better to be there with a multimeter.

I wish you were!

 

[3fordasho]

I know you are concerned about warranty - for that reason the manufacturer should fix this.

If I was not concerned about a warranty, the simplest solution would be to add a open on rise snap switch, either adjustable or appropriate fixed temperature, mount somewhere on plenum, wire in series with the thermostat. All low voltage, could be done with thermostat wire.

 

[laynes69]

Here's a link to the manual.....
https://napoleonproducts.com/downloads/hvac/manuals/updated/W415-1504.pdf


OK, I just want to vent a little about manufacturers websites and what they claim and want people to believe. I know the OP is from Canada.

I found this on their website:
View attachment 222031

As of November's EPA list of certified warm air furnaces, the HMF200 was not even on it. So, as of November 2017, it has not even passed the first phase of the certification, which is required to be able to be currently sold in the US. I also could not find ANY EPA data on their site what-so-ever. Their manual has not been updated per EPA requirements either.

Link to the list of EPA certified warm air furnaces: https://www.epa.gov/sites/production/files/2017-04/usepa-certified-forced-air-furnace-list.xlsx

Maybe it has passed phase 1 and will be on the next updated EPA list. Who knows, but it's obvious the company either doesn't have any real test data or they are trying to hide something.

What's the meaning to this post? Canada does not have to have an EPA certification, but they test to CSA B415.1-10, which would be their clean burn testing. I don't see them advertising EPA certified. They do meet phase one standards per EPA rules. I would assume as long as they meet tested requirements with CSA B415.1-10 they are perfectly legal to be sold in the US. With a 5 cu ft firebox and a rating of 4.5 grams an hour, that's pretty damn good. The poster didn't come on here to figure out whether his furnace is EPA certified or not, he came here for some help.

As for the OP, you are correct. The high limit should trip if there's an over abundance of heat in the plenum. Our Caddy (similar design) I think was set at 200 before the limit (high)would close. I think thats too hot myself, and I've lowered mine down to much lower to around 150-160. I can trip the high limit when I have a fresh load in the furnace, and it will close and open back up when its cooled. I wouldn't be comfortable at 250, but that's me. I'm going to say, it could very well be wired correctly, but at 250 degrees it would be impossible to trip the high limit with the blower running. The way we run our furnace ( I don't have any non factory mods), I open the damper and once the furnace is hot I close the damper and set the thermostat. Only when the fire is dying down, or it's super cold and there's a call for heat will it open. By me adjusting the high limit, it can bounce off the high and open and close the damper if there's a heavy call for heat. This way it burns much more efficient. As for the original 200 degree high limit for us.....I never hit it when it was there and the furnace would go nuclear before it even would come close!

 

[JRHAWK9]

What's the meaning to this post? Canada does not have to have an EPA certification, but they test to CSA B415.1-10, which would be their clean burn testing. I don't see them advertising EPA certified. They do meet phase one standards per EPA rules. I would assume as long as they meet tested requirements with CSA B415.1-10 they are perfectly legal to be sold in the US. With a 5 cu ft firebox and a rating of 4.5 grams an hour, that's pretty damn good. The poster didn't come on here to figure out whether his furnace is EPA certified or not, he came here for some help.

To provide some help to the OP with a link to the owners manual.

.....and to vent on a website that's useless as tits on a road grader for those who actually want to compare furnaces apples to apples. AFAIK, if it was legal to sell in the US it would be on the EPA's certified list. As soon as I saw "200,000 BTU's" I began the search for the real data behind their claim, which I found none. The OP DID mention "EPA" a handful of times in his original post, so one would assume being EPA certified was at least somewhat on his mind.

 

[Caydel]

To provide some help to the OP with a link to the owners manual.

.....and to vent on a website that's useless as tits on a road grader for those who actually want to compare furnaces apples to apples. AFAIK, if it was legal to sell in the US it would be on the EPA's certified list. As soon as I saw "200,000 BTU's" I began the search for the real data behind their claim, which I found none. The OP DID mention "EPA" a handful of times in his original post, so one would assume being EPA certified was at least somewhat on his mind.

In all fairness, I did assume it was EPA certified, but aside from that, I really more meant 'EPA style stove' in terms of the secondary gassifying burn.

In other news, I set the limit switch to 180 and did run a load. I'm not sure the limit switch every got hit even though the fire burnt at nuclear levels (I smelled the 'paint curing smell' for the first time in months). I did, however, monitor flu temps with an IR gun through the run. I saw surface temps on my single wall pipe up to 400 degrees 18" away from the collar at peak, which would correspond to 550-650 internal flu temps, but it dropped off from that.

In this run, the flu temps didn't get into 'danger' territory despite the primary damper being open the whole time. Firebox temp was very high (which would indicate a very complete burn).

 

[brenndatomu]

Man, no way I would put up with that...unhook the T-stat wires at the furnace and wire in a simple spring wound bathroom fan timer...at least then the damper will close at some point (of your choosing) and allow some of that heat to be put to the house instead of all up the chimney!
What's your burn time like? 2-3 hours?

 

[BradZ]

Caydel I tried to send you a message but thinking since I just joined it won’t let me.
I have never met anyone with this unit and I feel I am happy with it but also at time especially warmer outside temps I burn a lot of wood. Using the procedure you described, I take it your blower fan only kicks on when the the fan switch is tripped (150 I believe).

What’s your house sqft and cord consumption if you don’t mind me asking, I’m also from Ontario. Feel free to soon me a PM,
Cheers