Power Outage and LOTS of Smoke From Harman P38

TheGeneralLee · Oct 23, 2014

I was running the Harman last night when we lost power at our house for a few hours. The stove had a good fire going and all the hot embers and unburnt pellets smoldered once the power went out, creating a thick smoke inside the stove.

The problem is that smoke started leaking out of the bottom door where the ash bin goes and also leaked some out of the upper glass door. This tells me that the smoke is able to exit past the white rope gasket on both doors, which is disappointing considering the stove is not even two years old.

To give you an idea of setup, the stove does have an OAK and the exhaust pipe goes out the wall, then up about 4-5 feet outside. When I installed the stove, I made sure to add that vertical run on the exhaust, hoping it would create a natural upward draft for when the power does go out.

The only solution last evening was to quickly open the stove, scrape the hot embers into the pan, and throw them outside to prevent more smoke from building up in the stove. If this had happened later in the evening when we were asleep, I'm very concerned that the house would have filled with smoke to a dangerous level.

What's going on here, do all Harman's smoke some when the power goes out? Or do I have to replace my gaskets already? Any advice is really appreciated, thank you.

jdinny · Oct 23, 2014

We have our P43 plugged into a battery back up for a PC.
When power goes out, it cycles the exhaust fan till the fire goes out. Not sure if the P38 does it or not, but I would check it out.
Works great

TheGeneralLee · Oct 23, 2014

jdinny said:
We have our P43 plugged into a battery back up for a PC.
When power goes out, it cycles the exhaust fan till the fire goes out. Not sure if the P38 does it or not, but I would check it out.
Works great

Thanks, I am looking into that and from what I found on the forums, it sounds like most people start with at least a 1500 UPS.

I will do this, but I still am very curious if smoke coming out of the gaskets is normal or if I need to replace gaskets.

jdinny · Oct 23, 2014

We have ours plugged into a Cyberpower 825.
Mine has never smoked from the doors, but I would check on that if I were you.
The gaskets are probably inexpensive to replace anyway

jackman · Oct 23, 2014

TheGeneralLee said:
I still am very curious if smoke coming out of the gaskets is normal or if I need to replace gaskets.

Mine does the same. If you don't smell smoke when it's running normally I'd say your gaskets are fine. I have an APC SmartUPS 750 on my stove to keep it going long enough to shutdown in the event of a power outage.

TheGeneralLee · Oct 23, 2014

jackman said:
Mine does the same. If you don't smell smoke when it's running normally I'd say your gaskets are fine. I have an APC SmartUPS 750 on my stove to keep it going long enough to shutdown in the event of a power outage.

Thanks, and I should have mentioned before: when the stove is running, we do not have any smoke issues. It's only when the power goes out and there is a large amount of smoldering pellets in the pot, that's when it starts leaking smoke.

roadking88 · Oct 23, 2014

jackman said:
Mine does the same. If you don't smell smoke when it's running normally I'd say your gaskets are fine. I have an APC SmartUPS 750 on my stove to keep it going long enough to shutdown in the event of a power outage.

i have the same unit...shuts down with no smoke at all in the house..

Harvey Schneider · Oct 23, 2014

TheGeneralLee said:
The problem is that smoke started leaking out of the bottom door where the ash bin goes and also leaked some out of the upper glass door. This tells me that the smoke is able to exit past the white rope gasket on both doors, which is disappointing considering the stove is not even two years old.

Makes me wonder if the vent is (partially) obstructed.

TheGeneralLee · Oct 23, 2014

roadking88 said:
i have the same unit...shuts down with no smoke at all in the house..

When you say "shuts down" do you mean just turning the stove off? Mine also won't smoke when I turn it off and it has time to vent itself clean but last night was different because we lost power while the stove was burning.

TheGeneralLee · Oct 23, 2014

Harvey Schneider said:
Makes me wonder if the vent is (partially) obstructed.

Good thought but I checked the entire pipe and there are no obstructions. It also vents perfectly fine when there is power, this problem only occurred when power went out in the middle of a burn.

TimfromMA · Oct 23, 2014

I'm guessing your vent has little or no vertical rise. Mine doesn't either so I too use an APC battery backup. I've wired in bigger batteries to run for an extended time on battery power.

TheGeneralLee · Oct 23, 2014

TimfromMA said:
I'm guessing your vent has little or no vertical rise. Mine doesn't either so I too use an APC battery backup. I've wired in bigger batteries to run for an extended time on battery power.

Should have plenty of rise, it goes up 4-5 feet outside.

DMKNLD · Oct 23, 2014

What type of vent termination end cap do you have, and was the wind direction possibly causing down drafting in your vent? We have had strong NE winds in New England with the Nor'easter currently going on, and depending on the type of end cap you have this could have caused your smoke issues.

Harvey Schneider · Oct 23, 2014

TheGeneralLee said:
Good thought but I checked the entire pipe and there are no obstructions. It also vents perfectly fine when there is power, this problem only occurred when power went out in the middle of a burn.

Convection from the heat of the vent should have kept a small negative pressure in the firebox. If smoke was leaking out the bottom of the stove, the pressure in the firebox is higher than that in the room. Low room pressure could be cause by a competeing appliance such as a clothes dryer, kitchen or bath exhaust fan, water heater or furnace/boiler. Another cause of low house pressure could be air leaks cause by convection pulling air up around things that pass through the ceiling like light fixtures and vents.
Air won't go where it's not being pushed or pulled. The smoke just goes along for the ride. Under normal conditions your combustion blower can overwhelm the pressure differences. I think convection in the vent just wasn't up to it.

mepellet · Oct 23, 2014

A vent configuration of up and out is better than out and up. Too late now though unless you want to poke another hole in your wall.

Yardbird · Oct 23, 2014

Unless it's on a power backup, pretty much all stoves will allow smoke to seep out if there is a power loss. Natural draft doesn't work with pellet stoves. No power means no place for the smoke to go

TheGeneralLee · Oct 23, 2014

Thanks for the feedback everyone. For the questions on my vent, it's the standard DuraVent Pellet Vent Pro kit like this one: http://www.homedepot.com/p/DuraVent-3-in-Pellet-Stove-Vent-Kit-3PVL-KHA/100195128

DMKNLD said:
What type of vent termination end cap do you have, and was the wind direction possibly causing down drafting in your vent? We have had strong NE winds in New England with the Nor'easter currently going on, and depending on the type of end cap you have this could have caused your smoke issues.

DMKNLD, now that I think of it, I believe you nailed it on the head. We had strong northern wind gusts last night and that is the side of the house the stove intake/exhaust is on. I suspect that my gaskets may not be bad after all and the issue could have simply been due to the winds force smoke in rather than out.

Bottom line is it sounds like I need to invest in a UPS to help prevent this next time. Thanks again everyone.

Harvey Schneider · Oct 23, 2014

Yardbird said:
Unless it's on a power backup, pretty much all stoves will allow smoke to seep out if there is a power loss. Natural draft doesn't work with pellet stoves. No power means no place for the smoke to go

My experience says otherwise.
I've checked both my stoves by pulling the plug while they were at full fire. I didn't see smoke at all. The MVAE has 23 feet of hot vertical to help it draft. The PVDC has about 8 feet of vertical (basement dweller). Both stoves have OAK's.
Draft can pull air through the combustion blower even if it isn't running and hot air rises.

DMKNLD · Oct 23, 2014

TheGeneralLee said:
Thanks for the feedback everyone. For the questions on my vent, it's the standard DuraVent Pellet Vent Pro kit like this one: http://www.homedepot.com/p/DuraVent-3-in-Pellet-Stove-Vent-Kit-3PVL-KHA/100195128

DMKNLD, now that I think of it, I believe you nailed it on the head. We had strong northern wind gusts last night and that is the side of the house the stove intake/exhaust is on. I suspect that my gaskets may not be bad after all and the issue could have simply been due to the winds force smoke in rather than out.

Bottom line is it sounds like I need to invest in a UPS to help prevent this next time. Thanks again everyone.

It's tough for vent convection alone to overcome 35 - 45 mph wind gusts we've had blowing from an atypical direction like we've had, especially if your EVL is close to 15 using the 3" vent piping. To test your door gaskets you should do the 'dollar bill' test to make sure they hold the bill with a good bit of resistance. Would also be interesting to test your stove draft when there isn't a Nor'easter blowing like stink by pulling the stoves power plug for a bit to see if it back drafts - when you can plug it back in if it starts to smoke.

All that said , X2 on the value of a UPS - it will also help protect the longevity of your sensitive control board if you get frequent power surges like we do. A deep cycle battery back-up system will give you multiple hours of operation if your power goes out when your stove is running and no one is home to trouble shoot it.

Good luck, and stay warm today !!!

richkorn · Oct 23, 2014

Harvey Schneider said:
My experience says otherwise.
I've checked both my stoves by pulling the plug while they were at full fire. I didn't see smoke at all. The MVAE has 23 feet of hot vertical to help it draft. The PVDC has about 8 feet of vertical (basement dweller). Both stoves have OAK's.
Draft can pull air through the combustion blower even if it isn't running and hot air rises.

Agree. Have 25' vertical rise and no smoke if power goes out.

alternativeheat · Oct 23, 2014

Harvey Schneider said:
My experience says otherwise.
I've checked both my stoves by pulling the plug while they were at full fire. I didn't see smoke at all. The MVAE has 23 feet of hot vertical to help it draft. The PVDC has about 8 feet of vertical (basement dweller). Both stoves have OAK's.
Draft can pull air through the combustion blower even if it isn't running and hot air rises.

Ya my P61 doesn't smoke either in an outage, it's on a 26' run of 4" vertical liner. We lost power and the flame just went all lazy ( natural looking vs forced air) until the pellets burned out. In fact I can clean my P61, scrape/brush ash down and with the door open and the ash just goes away. The only amount that might get in the room a bit is when brushing the header over the door. So I have negative draw in my stove without the stove running with that rise.

thundercracker · Oct 23, 2014

so if i get a new battery back up like the APC BE-750G, i just plug the stove into the APC, then the APC into the outlet?

if power goes out, i'll have a couple minutes on the APC to shut down the stove? i really want to minimize smoke into the house.

jdinny · Oct 23, 2014

From the Harman P43 manual:

Addendum
Minimizing Smoke During Loss of Power Using Battery Back-up
HarmanTM strongly recommends installing battery back-up to minimize entry of smoke into the

room in the event of power loss.
Your pellet/biomass burning appliance relies on a combustion blower to remove exhaust. A power failure
will cause the combustion blower to stop. This may lead to exhaust seeping into the room. Vertical rise
in the venting may provide natural draft. It is, however, no guarantee against leakage.
There are two HarmanTM approved battery back-up options for your appliance:
Uninterruptible Power Supply (UPS) UPS battery back-ups are available online or at computer and
office equipment stores. Your HarmanTM appliance with Rev E or later software available beginning in
November 2010 may be plugged directly into a HarmanTM approved UPS:
• The APC (American Power Conversion) model #BE750G and the TrippLite model
INTERNET750U are tested and approved. Other brands or models may not be compatible.
When power is lost, a fully charged UPS will power a safe, combustion blower only shut-down. Your
appliance will pulse the blower every few seconds to clear exhaust until the fire is out. NOTE: The UPS

provides safe shut-down only. It is not intended for continued operation.
Your appliance will recognize when power is restored. What happens depends on ESP temperature
and whether it is equipped with automatic ignition:
• In “Automatic” setting, units equipped with automatic ignition will respond to the set point
and ESP temperature and resume normal operation.
• In “Manual” setting or for units without automatic ignition:
• If the ESP is cool, the appliance will remain shut down.
• If the fire is out and the ESP is still warm, the feeder may restart. Since the fire is out, the
ESP temperature will not rise. The unit will then shut-down, and may flash a six-blink status
error. (See ESP error codes)
• If the fire is still burning, it will resume normal operation.
Contact your dealer if you have questions about UPS compatibility with your appliance.
Harman Surefire 512H Battery Back-up The 512H connects to a 12 volt deep cycle battery that will

run your appliance for up to eight (8) hours. It includes a trickle charge feature that keeps your battery
charged when power is available. NOTE: If the power is out for longer than battery life, smoke

leakage may still occur unless your stove has been safely shut down.
CAUTION! Always keep appliance doors and hopper lid closed and latched during operation
and during power failures to minimize risk of smoke or burn-back.
CAUTION! Use only HarmanTM approved battery back-up devices. Other products may
not operate properly, can create unsafe conditions or

roadking88 · Oct 23, 2014

thundercracker said:
so if i get a new battery back up like the APC BE-750G, i just plug the stove into the APC, then the APC into the outlet?

if power goes out, i'll have a couple minutes on the APC to shut down the stove? i really want to minimize smoke into the house.

yes plug in the wall then stove to apc .. when you lose power the stove will run of and on until there it is safe to shut itself down..mine runs probably 30 minutes going on then off.
no smoke and no vertical rise at all ..

jdinny · Oct 23, 2014

roadking88 said:
yes plug in the wall then stove to apc .. when you lose power the stove will run of and on until there it is safe to shut itself down..mine runs probably 30 minutes going on then off.
no smoke and no vertical rise at all ..

Same here, no smoke, and no vertical rise either.
Vent pipe goes straight outside

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