Anyone swap their proof of fire switch for a lower range switch?

[Snowmobileaddict]

I am currently running a BOSCA 500 Classic with OAK on a programmable thermostat in on/off mode.

Because the proof of fire (POF) switch tells the main board how long the exhaust blower will run during a normal shut-down sequence I am considering going to an adjustable type switch or at minimum going to switch that will actuate at a lower temperature, thereby letting the exhaust blower run a little while longer during normal shutdown.

I’d like to do this in order to reduce the chance of having any smoldering pellets remaining in my burn pot after a normal shutdown sequence is complete.

Because I am using an OAK, cold air is being drawn in across the burn pot during a shut-down sequence. My thinking is that this cold winter air could lower exhaust temps to the point that my stock POF switch thinks that the fire in the burnpot is completely out and snap open, thereby telling the main board to complete the stove shutdown sequence and turn off the exhaust blower. However, if there happens to be a small amount of smoldering pellets in the burnpot, a smoke-back situation could occur into the house.

All in all, I’m just seeking some extra exhaust blower time during a normal shutdown.

Thoughts comments appreciated!

 

[jtakeman]

I wouldn't go too much lower than 120ºF. I know the POF closes at 120º on most stove, But I think it doesn't open until the temp drops to 110ºF. Adjustable is a good ideal. What switch are you thinking of?

Interesting and hopefully it works for you. Keep us posted.

 

[SmokeyTheBear]

I am currently running a BOSCA 500 Classic with OAK on a programmable thermostat in on/off mode.

Because the proof of fire (POF) switch tells the main board how long the exhaust blower will run during a normal shut-down sequence I am considering going to an adjustable type switch or at minimum going to switch that will actuate at a lower temperature, thereby letting the exhaust blower run a little while longer during normal shutdown.

I’d like to do this in order to reduce the chance of having any smoldering pellets remaining in my burn pot after a normal shutdown sequence is complete.

Because I am using an OAK, cold air is being drawn in across the burn pot during a shut-down sequence. My thinking is that this cold winter air could lower exhaust temps to the point that my stock POF switch thinks that the fire in the burnpot is completely out and snap open, thereby telling the main board to complete the stove shutdown sequence and turn off the exhaust blower. However, if there happens to be a small amount of smoldering pellets in the burnpot, a smoke-back situation could occur into the house.

All in all, I’m just seeking some extra exhaust blower time during a normal shutdown.

Thoughts comments appreciated!

You can have smoldering pellets in the burn pot even if you had a 90 low limit.

The smoke back situations can be prevented by having a natural draft. This forces the exhaust gases to exit through the vent until you do something like open the stove's door.

 

[Snowmobileaddict]

I wouldn't go too much lower than 120ºF. I know the POF closes at 120º on most stove, But I think it doesn't open until the temp drops to 110ºF. Adjustable is a good ideal. What switch are you thinking of?

Interesting and hopefully it works for you. Keep us posted.

White Rogers adjustable 3F05-1. 90-130f adjustable actuation range.

 

[SmokeyTheBear]

According to the specifications that snap disc has a 20 operating differential and if set for 90 it will open at 70 .

There are a number of folks on here that have used those kinds of switches to extract more of the heat that might have gone up the flue before the convection fan starts or before that fan stops.

 

[chamas]

Is that the snap disc that is located on the combustion blower housing?

 

[Snowmobileaddict]

Is that the snap disc that is located on the combustion blower housing?

Proof-of-Fire (Low Limit) snap disc is located on my combustion blower housing

 

[Hellfire]

However, if there happens to be a small amount of smoldering pellets in the burnpot, a smoke-back situation could occur into the house.

One option.


Wire a toggle switch (a lighted style to remind you to switch off)to manually bypass the P.O.F. ?

Just don`t forget to set it back off to resume normal operations retaining the P.O.F

Still wondering what you are trying to gain

 

[SmokeyTheBear]

He is worried about the stove shutting down with smoldering pellets in the burn pot because of winter time outside combustion air temperatures possibly faking out the low limit switch, perhaps causing smoke back into the house.

 

[Don2222]

Hello

I have rebuilt a few stoves now.
I find that some stoves do not have the best snap disc for the location it is mounted in. So if I were you I would try changing it for better results. If you have a standard 3/4" airstream mount low limit switch that is close on rise, try changing it to one of these Selco switches. They are the best quality I have found and are quite accurate too.

http://catalog.selcoproducts.com/vi...-disc-se-series-airsteam-mount-close-on-rise?

They also have the surface mounts too.

I know people who went to the 100 or even 90 Deg F switch to achieve what you want with no problems.

 

[Hellfire]

He is worried about the stove shutting down with smoldering pellets in the burn pot because of winter time outside combustion air temperatures possibly faking out the low limit switch, perhaps causing smoke back into the house.

I just got confused on what the actual problem (possible smoke?)< i would worry more Vs.(just some extra heat extraction)
Either way their covered.

could occur into the house.

All in all, I’m just seeking some extra exhaust blower time during a normal shutdown.

Another viable option:


Wire it through a digital timer ,setting it`s shut down with the delay time you choose

 

[Snowmobileaddict]

My objective is to give longer ΔT between when the T-Stat is satisfied and when the low limit switch opens and signals the stove to turn off the exhaust blower. I only want to do this to give any burning pellet remants in the burnpot liner more time to burn out and help to prevent smoke-back after a normal shut down.

I understand that natural draft will help prevent smoke back on many stoves and I am within spec for max EVL on a 3" pipe and I do have a 60" vertical rise. However, not all fireboxes are identical. For example, like may stoves, my unit does have a small opening into the firebox for the heat exchanger tube cleaner rod to pass through the front of the stove. Also, my unit has 7 excahnger tubes that are not sealed to the firebox. There is a small unsealed annular space around each of them as well as an air-wash gap along the top edge of the ceramic viewing glass.

These gaps are all engineered into the stove and do not present a problem when it is running and the firebox is well within intended negative pressure specs. However, these openings are all at the top/front of the firebox and my strove directs the combustion gases up then back then slightly down through the comustion blower fan blades and then finally up and out the 3" vent.

When the stove shuts down, even with a mild natural draft working in my favor, the path of least resistance on my stove can unfortunatley be out and into our living space (especially when someone upstairs is running bathroom fan and the gas dryer is running. It is under these condtions that I have expericed one mild smokeback after a normal shutdown.

I might add however, that this occured after about 3 days of running the stove on on/off T-Stat mode ( appx 18 cycles) without cleaning off the burnpot liner. What had happend was the burnpot liner holes were partially obstructed with something in between clinker and ash and the stove completed it's normal shut down sequence before a small piece of smoldering pellet had completely burned out. This partially obstructed burnpot liner was likely impeding combustion air flow through the burn pot preventing the smoldering pellet piece from completly burning out.

My stove doesn't have an agitatior or an automated burnpot scraper, so the burnpot liner does need to be checked/cleaned daily. I recognize that and that having a different low-limit switch does not replace daily stove maintenance. Lesson 1 is 99% of all stove problems come from a dirty stove.

 

[SmokeyTheBear]

If you have issues with negative pressure in your house you might want to look into that all by itself as it isn't a good thing in general.

As I said earlier having the low limit run the blower for a longer period of time does not guarantee the absence of smoldering pellets in the burn pot.

Just about every pellet stove has an air gap somewhere around its window glass and most tube scrapper rods penetrate the firebox.

If there is sufficient natural draft the smoke goes out the vent this requires that the natural draft be able to overcome the negative pressure in your house where the stove is.

My stove has a scrapper rod penetration and air wash, it is also in a lower level room (basement) and subject to any chimney effect fans in the house can cause, it is OAKed, I clean my stove once a week, I've had enough mess in the pot to qualify as a hazardous waste dump and under these conditions it has smoldering pellets, my vent is 3" my evl is 14.5 no smoke back into the room.

You can change the low limit switch just remember that it is possible that the low limit will keep the stove blowers running even when you might not want them to if it is set too low.

 

[saladdin]

My objective is to give longer ΔT between when the T-Stat is satisfied and when the low limit switch opens and signals the stove to turn off the exhaust blower. I only want to do this to give any burning pellet remants in the burnpot liner more time to burn out and help to prevent smoke-back after a normal shut down.

I understand that natural draft will help prevent smoke back on many stoves and I am within spec for max EVL on a 3" pipe and I do have a 60" vertical rise. However, not all fireboxes are identical. For example, like may stoves, my unit does have a small opening into the firebox for the heat exchanger tube cleaner rod to pass through the front of the stove. Also, my unit has 7 excahnger tubes that are not sealed to the firebox. There is a small unsealed annular space around each of them as well as an air-wash gap along the top edge of the ceramic viewing glass.

These gaps are all engineered into the stove and do not present a problem when it is running and the firebox is well within intended negative pressure specs. However, these openings are all at the top/front of the firebox and my strove directs the combustion gases up then back then slightly down through the comustion blower fan blades and then finally up and out the 3" vent.

When the stove shuts down, even with a mild natural draft working in my favor, the path of least resistance on my stove can unfortunatley be out and into our living space (especially when someone upstairs is running bathroom fan and the gas dryer is running. It is under these condtions that I have expericed one mild smokeback after a normal shutdown.

I might add however, that this occured after about 3 days of running the stove on on/off T-Stat mode ( appx 18 cycles) without cleaning off the burnpot liner. What had happend was the burnpot liner holes were partially obstructed with something in between clinker and ash and the stove completed it's normal shut down sequence before a small piece of smoldering pellet had completely burned out. This partially obstructed burnpot liner was likely impeding combustion air flow through the burn pot preventing the smoldering pellet piece from completly burning out.

My stove doesn't have an agitatior or an automated burnpot scraper, so the burnpot liner does need to be checked/cleaned daily. I recognize that and that having a different low-limit switch does not replace daily stove maintenance. Lesson 1 is 99% of all stove problems come from a dirty stove.

You afraid the stove is going to get out of its cage and run amuck?

I've never seen that setup. Great idea.

 

[Hellfire]

I might add however, that this occured after about 3 days of running the stove on on/off T-Stat mode ( appx 18 cycles) without cleaning off the burnpot liner. What had happend was the burnpot liner holes were partially obstructed with something in between clinker and ash and the stove completed it's normal shut down sequence before a small piece of smoldering pellet had completely burned out. This partially obstructed burnpot liner was likely impeding combustion air flow through the burn pot preventing the smoldering pellet piece from completly burning out.

IMO & also my preference i do not use a t-stat at all (manual operation only)

Just more problems.

? have you ever run manually on a high heat setting prior to shut down (vs. shut down in t-stat mode),thus obtaining a (better)full & complete burn prior to shut down?
+ the bonus of a cleaner stove loading up with byproducts because of a less than optimum burn (T-stat mode is more for comfort for you ,not sure on the stove though) seems like the culprit to me.

 

[SmokeyTheBear]

You afraid the stove is going to get out of its cage and run amuck?

I've never seen that setup. Great idea.

He did nice job there especially for the little one.

 

[Hellfire]

Maybe he`s a pellet pig.

No escape.

Now we don`t want an epidemic ,can only feed one pig at a time seeing times are tough.

 

[Snowmobileaddict]

Maybe he`s a pellet pig.

No escape.

Now we don`t want an epidemic ,can only feed one pig at a time seeing times are tough.

Ha!

No pig here, We do have a 21month old daughter and our second daughter is due any day now. thats why I opped for the KidCo Hearth gate and put our Bosca in "Jail"

 

[SmokeyTheBear]

Ha!

No pig here, We do have a 21month old daughter and our second daughter is due any day now. thats why I opped for the KidCo Hearth gate and put our Bosca in "Jail"

If I had little ones around my stove would be in jail as well.

 

[Hellfire]

Bosca in "Jail"

So your pig`s named Bosca.

No parole till spring.

An occasional grooming i mean cleaning once in a while is all that`s needed.

Keep warm.

 

[Snowmobileaddict]

IMO & also my preference i do not use a t-stat at all (manual operation only)

Just more problems.

? have you ever run manually on a high heat setting prior to shut down (vs. shut down in t-stat mode),thus obtaining a (better)full & complete burn prior to shut down?
+ the bonus of a cleaner stove loading up with byproducts because of a less than optimum burn (T-stat mode is more for comfort for you ,not sure on the stove though) seems like the culprit to me.

The whole reason we chose pellet heat for our application is because it is T-Stat capable technology and was way cheaper than adding a second zone to our existing forced air system just for our newly finished basement. We got our stove brand new on the pallet for $1000 cash out the door. Add on another $300 for vent and $150 for the hearth gate and we saved better than $2K over the zone addition (low bid was $3500 to add a zone to our forced air system).

This unit is in a finished, insulated basement with a bedroom off of one end of it. Total space to heat is 700 sf. When its gets colder this winter I may try going to Hi/Lo stat mode but I suspect that it won't work for us without overheating the basement. We have natural gas and a newer furnace to heat the rest of the house so, we aren't trying to save money by subbing pellets for nat gas and using our stove to heat the rest of the house.

 

[Snowmobileaddict]

So your pig`s named Bosca.

No parole till spring.

An occasional grooming i mean cleaning once in a while is all that`s needed.

Keep warm.

Well, Bosca the brand name. I haven't gone so far to name my stove yet.

http://www.woodlanddirect.com/Wood-Stove-and-Accessories/Wood-Stoves-Brand-Bosca

 

[Hellfire]

(low bid was $3500 to add a zone to our forced air system).

Ouch!

When its gets colder this winter I may try going to Hi/Lo stat mode but I suspect that it won't work for us without overheating the basement

Won`t hurt to try ,the worst that will happen is you will break a little sweat.

Good luck

 

[SmokeyTheBear]

Talk to us about the flow rate on your forced hot air furnace (large air mover) and where the ducting runs relative to your stove room.

 

[Snowmobileaddict]

I don't have specs for our furnace with me regarding CFM. I do know that it could have handled the extra zone no problem all 3 HVAC contractors that came through confirmed that.

Furthermore, because pellet fuel is more expensive per them than natural gas, we decided against trying to use a pellet stove for the basement as a whole home heat solution. From a total cost of operation standpoint if you try to figure in kwh for running distribution fans it’s probably a wash between the two. We decided that any heat that happens to make its way up the stairwell and into the family room would simply be a bonus

As such, when we chose pellet heat for the basement we eliminated all supply and return air fixtures in the basement. The main trunk does run through the middle of the room as shown below but it is sealed, framed and sheetrocked over.