Baro and manual dampers

Dave's is more proof of how the situations can vary. Even in the same house.

Now that I'm using two chimneys, each with a mano connected to it, during wind gusts, when the baro was operational for the chimney in the center of my house, the mano showed easily double the amount of reading change as the chimney at the back of the house.

I suspect the wind gusts hitting the large cross-gabled roof with that central chimney near the cross of those gables, causes greater pressure changes across the top of that chimney. And that was with an 8 inch baro connected in that chimney system. One other difference is that chimney does not have a slate cap on it like the others

Oddly though, since I blocked off that baro, the mano readings have been more stable. Not sure why, yet.

Paul

scalabro wrote: ↑

Tue. Feb. 13, 2018 9:12 pm

Can someone please explain why (physics please) all three of these devices can’t be used together to maximize efficiency?

(Lightning eagerly raises his hand with a look of enthusiasm written on his face, "pick me! pick me!" The class flueologist rolls his eyes with a look of reservation and says,"okay Mr. Lightning, please come up to the chalk board and explain.....")

Well first let's define the function of each.
Metallic thermostat - holds set stove temperature steady by controlling primary combustion air volume, responds to stove temperature
Baro damper - holds draft steady at set pressure
MPD - flue gas exhaust choke, limits flue gas by reducing flue pipe volume capacity

Can all of these be used to increase efficiency? I would like to add/modify that question to ask, "Can all of these be used to increase efficiency AND keep reliable heat output?" I will say yes, and will attempt to demonstrate how.

So in this scenario we will use a run of the mill batch fed coal stove on the first floor of the living area. It's connected to an interior brick and mortar chimney that runs up thru the center of the house to the peak at a height of 30 feet. The gas configuration path is metallic thermostat - stove - baro damper - MPD - chimney. I see the eye brows rising with the MPD above the baro, but I will explain.

On a cold day our stove is running hard keeping me toasty warm with radiant heat as I lounge beside it in my recliner. I look to the manometer and notice it's reading -.04" which is a little higher than I like for cruising pressure which is closer to -.03. With a glance at the baro I see the baro door is wide open using quite a high volume of warm room air in its attempt to hold the draft at it's set pressure. I'd like to pause here and say that some people think that this warm room air going into the chimney is a waste. Maybe it is. Some people think it creates more cold air infiltration, maybe it does. My personal thought is that it's using air infiltration that would occur regardless. So, for now let's assume the worst that it's wasting warm room air up the chimney and creating extra cold air infiltration. Here is where the MPD above the baro comes in. I slowly twist the MPD from its full open position while watching the baro door. As the volume capacity of the pipe is reduced, the baro door starts to swing towards it's closed position. But I don't want to continue twisting the MPD until the baro door closes completely, I just want to reduce the amount of room air it's using so it can do it's job more efficiently and effectively to keep draft pressure at it's set of -.03. I look to the mano to see that is the case now.

While I was standing up to adjust the MPD I notice the pine tree outside swaying in the wind. I look at the baro door and see it rocking just slightly, tamed by the partially closed MPD above it. The mano is holding -.03 with the now effortlessly functioning baro.

I lay back down in the recliner and fall asleep. It's morning now and my stove has been keeping me warm all night. It's starting to ash up a bit but still holding 450 degrees. I glance at the metallic thermostat and see that it has opened some. Also, I realize thru the night that the stove didn't need to yo yo it's heat output at all to force the metallic thermostat to control the stove's heat output nor did excessive secondary air get pulled in due to fluctuating draft pressure.

Here my friends, is the perfectly controlled stove in its most efficient configuration.

Edit - fixed typos

Ok Lee, but the question still remains,.... will it actually happen like that ? Theory or fact?

Paul

oliver power wrote: ↑

Wed. Feb. 14, 2018 2:26 am

... The bi-metallic damper controlled the HITZERs. If set up/adjusted correctly, the bi-metallic damper does respond instantly to wind gusts. When the wind draws on the chimney, the tin flapper door closes.

The Hitzer bi-metal damper is different from some others -- larger surface area and fairly light in weight. So yes, it can be pulled shut fairly easily by strong chimney draw. I have never seen that happen with my DS Machine intake. Also the Hitzer intake is fitted with a magnet so when the wind draws it shut, it is more likely to STAY shut after a wind gust has passed, drawing minimum air through the ash door vents. Very clever design, all in all, and I can see why it might need no MPD or baro.

Sunny Boy wrote: ↑

Wed. Feb. 14, 2018 9:18 am

Ok Lee, but the question still remains,.... will it actually happen like that ? Theory or fact?

Paul

Due to the experimentation of the MPD above the baro I've done and based on knowledge of how a metallic thermostat works, I believe it would happen exactly how I described it

Dr. Lee, please move to the front row of the class, well done! As you know I prefer the MPD before the baro, simply because an overnight weather change could possibly kill draft easier, causing a reversal with the MPD “choking” down the chimney. And this could happen while you were resting comfortably in your chair.

You should write a “Coal Christmas Story”

Hahahahaha

Too bad the barometrically controlled MPD was never developed

scalabro wrote: ↑

Wed. Feb. 14, 2018 9:42 am

Too bad the barometrically controlled MPD was never developed

I could use such a piece on my exhaust pipe.

scalabro wrote: ↑

Wed. Feb. 14, 2018 9:42 am

Dr. Lee, please move to the front row of the class, well done! As you know I prefer the MPD before the baro, simply because an overnight weather change could possibly kill draft easier, causing a reversal with the MPD “choking” down the chimney. And this could happen while you were resting comfortably in your chair.

You should write a “Coal Christmas Story”

Hahahahaha

Too bad the barometrically controlled MPD was never developed

Thanks Scott, I understand the concern with the MPD above the baro. If weather changes occurred to force draft pressure to weaken below the set pressure of the baro (-.03) it would also lessen combustion air entering the stove. This would cause the stove to cool slightly and the metallic thermostat would respond by opening. With more combustion air entering the stove now, it would continue it's set heat output and force the draft to comply with it's set pressure of -.03. The metallic thermostat would actually act as safety net to prevent a draft failure until the stove ran out of fuel.

As long as your pausing, I'd like to clear up one thing.

" ............. I'd like to pause here and say that some people think that this warm room air going into the chimney is a waste. Maybe it is. Some people think it creates more cold air infiltration, maybe it does. My personal thought is that it's using air infiltration that would occur regardless. ..............."

Baros using warmed room air and causing more cold air infiltration to make up for it is not opinion, it is easily proven fact.

And for the sake of this we'll stick to exhaust side control choices, which eaves out bi-metal flapper dampers.

Lets pick some letters for ease of an equation to illustrate.

Lets say a stove needs "X" amount of air to maintain a specific heat output that you want to keep it at. If it climbs above that output it's because it is burning more room air. We'll call that "X+M". So we have a few ways to help prevent that "X+M" increase on the exhaust side of the system.

With using a baro for stove output control, we know it takes in room air to reduce exhaust temps, thus reducing draft strength which causes "X+M". So lets call that amount, "B" air.

We know an MPD works by causing resistance to exhaust gas flow thereby slowing it's speed through the stove pipe and chimney system, thus reducing draft strength by resistance. To keep the stove at "X" room air usage with a MPD, it needs no additional air. So, only "X" amount of air is taken from the room and needing to be replaced by a cold air infiltration source.

To keep the same stove at "X" air usage with a baro, it will still need X amount of air to maintain the same heat output, but it will need the addition of "B" air to control the draft to keep the stove at "X"air usage. That additional "B" air has to be made up for, which is also from an outside, cold air source.

So, simply put,....

1. An MPD equals "X" amount of air use and therefore "X" amount of cold air infiltration to make up for that.
2. A baro equals "X+B" amount of air use and therefore "X+B" amount of cold air infiltration to make up for that increased air needed for "B" to work.

So, with a baro, your now getting more like "X+M", which is what we wanted to prevent in the first place.

Paul

Hahahahaha Sunny.....excellent point!

This is why the baro controlled MPD must be developed

scalabro wrote: ↑

Wed. Feb. 14, 2018 10:21 am

Hahahahaha Sunny.....excellent point!

This is why the baro controlled MPD must be developed

I'll get right on it.

Paul

Sunny Boy wrote: ↑

Wed. Feb. 14, 2018 10:14 am

Baros using warmed room air and causing more cold air infiltration to make up for it is not opinion, it is easily proven fact.

I'll need further review to get a grip on your algebra lol. But for the statement above, I'd like to respond by saying it's a little more complicated. There is house stack effect to consider and what effect an operating baro has on the neural pressure plane. For cold air infiltration to occur, warm air must leave the house at the top level. It's possible that some of that warm air destined to leave the house at the top level is rerouted thru the baro door, keeping any extra cold air infiltration that would be thought to be caused by the baro very minimal. That's why I believe it's debatable, but likely unable to be proven.

Edit - that is why I would choose the MPD above the baro, to keep room air loss minimal while also allowing the baro to do it's job more effectively without being overwhelmed in its effort to maintain the set draft pressure.

No, it really is quite simple. People who don't understand what's actually happening are only confusing the issue. Stack effect pressure has nothing to do with how which draft control works on the exhaust side.

"Stack effect" effects both intake and exhaust sides of the stove equally, therefore it is not a factor and only serves to confuse the issue

There is no way you can feed air to both the stove and the baro without making up that additional air usage that the baro needs from outside the house. Baro's can not "create" air inside the house. What they do is bypass the excess air the stove would have used to burn hotter. But they still need that additional air to come into the house or they could not work.

This is not based on opinion, it is provable science. If you isolate the air feeds to the stove and to the baro, you can then actually measure and see the air needed for each to do their job.

Here's a simple test of a baro's increased air need. Cover the baro over so you know for certain that it can't take additional air from inside the house. Guess what happens.

Paul

I hate to say it Lee, but sometimes I think you could complicate a PB & J sandwich. Hell, you're getting right up there with Larry. .>) PS--that's why I added that 6" pipe running from the outside to my oil furnace to create the air the Baro needs.

For whatever its worth I am not going to recommend a MPD above the baro for safety reasons. One of those "dont try this at home" statements. We dont need to read in the paper about someone getting CO poisoning from following this advice..... I do realize you all have CO detectors and know what you are doing. Many people dont.

OK, I said that. Carry on now if you must Interesting theories.