To Barometric Damper or Not To

[morningwood]

This is for the wood furnace guys.

I recently put an addition on my house. The HVAC company installed a PSG Caddy furnace inline with our geothermal furnace in our basement. I live in Central Ohio and things are starting to get cold so I would like to fire up the Caddy for the first time. I have 14' of double wall stainless and approximately 4 feet of black pipe.

<a href="https://picasaweb.google.com/lh/photo/N_dFkaJgsYoMHtG7nyOjJtgUGniCDQuuCQm1bLnJPmM?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-hybKcifqoes/Ts2jTLxHlYI/AAAAAAAAAJk/n7FMr_vqMzE/s144/photo%2525201.JPG" height="144" width="108" /></a>

<a href="https://picasaweb.google.com/lh/photo/d8CnI7m2DluQPM_LbYkSOtgUGniCDQuuCQm1bLnJPmM?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-DPWDTk2mSKc/Ts2jShulUCI/AAAAAAAAAJc/gIFzojkNHPE/s144/photo%2525202.JPG" height="144" width="108" /></a>

The poorly written and illustrated PSG manual quotes the following:

DAMPER

If the draft exceeds -0.06 w.c., a barometric damper must installed. The barometric damper must be adjusted so
that the maximum draft measured at the furnace outlet is limited to -0.06 in. w.c. Please note that a draft higher than
-0.06 w.c. will reduce efficiency and could result in an uncontrollable fire. On the other hand, the minimum draft
to be respected is -0.04 in. w.c. in the evacuation pipe on the solid fuel side, no matter what type of furnace
(WOOD, WOOD / ELECTRIC OR WOOD / OIL)."

My question is, how do I test the draft and where ? Do I test it in front of the damper or within the chimney.

Thanks,

Scott

P.S. - Please no PSG vs Yukon bantering and no "the caddy is not a EPA certified wood furnace".

 

[laynes69]

I think the manual is very specific. If during the install the draft tests over .06" then a baro would be required. With a 14' chimney, I would not worry about running one. You may exceed that draft from time to time, but 14' is a fairly small chimney. Installing a baro would do more harm than help with a chimney that size. If you wanted to test, a simple 1/4" hole drilled in the flue pipe at the exhaust of the furnace would allow for an insertion of a manometer. Fire it up!

 

[Whitespider]

My personal opinion on the Barometric Damper is "NOT!"
I'd go with a manual flue damper (with any wood-burning appliance) because I like complete and total control.

 

[laynes69]

I'd agree with you Whitespider, but the damper controls for the Caddy are automatic via thermostat. Because of this a manual damper is not recommended. If the furnace was controlled by hand then I think a manual damper would be fine.

 

[Whitespider]

Hmmmm....... guess I'm just not up on all these new-fangled wood burners. Automatic dampers, intake blowers, thermostats, baro-dampers, stainless flues/chimneys, cats, secondary burn thingys, glass doors... maybe I'll just become a bitter old man that can't let go of the past... No... Wait... I can't do that 'cause I managed to figure out computers... but I still have no clue how to send a text message.

 

[laynes69]

Hmmmm....... guess I'm just not up on all these new-fangled wood burners. Automatic dampers, intake blowers, thermostats, baro-dampers, stainless flues/chimneys, cats, secondary burn thingys, glass doors... maybe I'll just become a bitter old man that can't let go of the past... No... Wait... I can't do that 'cause I managed to figure out computers... but I still have no clue how to send a text message.

Lol, took me a while to get into the new fangled wood furnace's also, but glad I did! Also lining the chimney was a good performance boost. I repair computers and love electronic gadgets, so I figured I might as well upgrade the old furnace. I'm an energy buff, and also a penny pincher. If I can cut my wood consumption, chimney maintenance, etc. why not?

 

[Fyrebug]

This is for the wood furnace guys.

I recently put an addition on my house. The HVAC company installed a PSG Caddy furnace inline with our geothermal furnace in our basement. I live in Central Ohio and things are starting to get cold so I would like to fire up the Caddy for the first time. I have 14' of double wall stainless and approximately 4 feet of black pipe.

<a href="https://picasaweb.google.com/lh/photo/N_dFkaJgsYoMHtG7nyOjJtgUGniCDQuuCQm1bLnJPmM?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-hybKcifqoes/Ts2jTLxHlYI/AAAAAAAAAJk/n7FMr_vqMzE/s144/photo%2525201.JPG" height="144" width="108" /></a>

<a href="https://picasaweb.google.com/lh/photo/d8CnI7m2DluQPM_LbYkSOtgUGniCDQuuCQm1bLnJPmM?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-DPWDTk2mSKc/Ts2jShulUCI/AAAAAAAAAJc/gIFzojkNHPE/s144/photo%2525202.JPG" height="144" width="108" /></a>

The poorly written and illustrated PSG manual quotes the following:

DAMPER

If the draft exceeds -0.06 w.c., a barometric damper must installed. The barometric damper must be adjusted so
that the maximum draft measured at the furnace outlet is limited to -0.06 in. w.c. Please note that a draft higher than
-0.06 w.c. will reduce efficiency and could result in an uncontrollable fire. On the other hand, the minimum draft
to be respected is -0.04 in. w.c. in the evacuation pipe on the solid fuel side, no matter what type of furnace
(WOOD, WOOD / ELECTRIC OR WOOD / OIL)."

My question is, how do I test the draft and where ? Do I test it in front of the damper or within the chimney.

Thanks,

Scott

P.S. - Please no PSG vs Yukon bantering and no "the caddy is not a EPA certified wood furnace".

If I may... Your warm air plenum is non-standard and you may have some issues with it. The manual recommends for it to be sized the same as the furnace for a minimum of 18". Have you taken a static pressure reading? Because the way it's set up it looks as if you would have too much static pressure and overheating the furnace. Because of the plenum design, It also looks as if the fan limit control might not be at the right place, which would also impact the performance of the unit.

I'm not saying it wont work, just saying that there's a chance you might not get the best performance out of the unit until the plenum is designed to spec.

 

[morningwood]

Laynes,

Thanks for the information. I wish PSG would include that information in the manual.

I am planning on firing up the furnace up next week so I will see how it draws.

Thanks,

Scott

 

[morningwood]

If I may... Your warm air plenum is non-standard and you may have some issues with it. The manual recommends for it to be sized the same as the furnace for a minimum of 18". Have you taken a static pressure reading? Because the way it's set up it looks as if you would have too much static pressure and overheating the furnace. Because of the plenum design, It also looks as if the fan limit control might not be at the right place, which would also impact the performance of the unit.

I'm not saying it wont work, just saying that there's a chance you might not get the best performance out of the unit until the plenum is designed to spec.

Fyrebug,

Kinda of a long story. I will give you the abbreviated version. :wink:

Our existing house does not have basement and our addition did. The only way that we could tie the wood burning furnace into the new duct work and have it feed both the addition and new house was to pipe it into the plenum of the new geothermal furance which limited the height on the PSG plenum. We also had to work around where the flue came into the basement.

I believe the existing plenum is 8" or 9" tall. The pipe coming out of the top of the PSG plenum is 14" which is rated for 700CFM. I do not have a manometer to measure water column. I do have a friend who is a commercial HVAC tech and I am sure he has one.

What should the height of the PSG plenum be ? I could have one built and tie the 14" pipe into the side of it ?

Attached is a close up pic of both plenums.

Thanks,

Scott

 

[laynes69]

Morning, did they install a backdraft damper below the woodfurnace's duct into the plenum of the geothermal? I built a reduced plenum for clearances on our woodfurnace, but did a take off for a smooth run into the trunk. Our static pressure tested okay.

 

[morningwood]

Morning, did they install a backdraft damper below the woodfurnace's duct into the plenum of the geothermal? I built a reduced plenum for clearances on our woodfurnace, but did a take off for a smooth run into the trunk. Our static pressure tested okay.

Laynes,

In order to keep the hot air off of the geo coil I am just going to run the geo's fan when the wood furnace is running. The geo fan is set to run at around 800CFM and I have the wooburner's fan set at the lowest speed.

We thought this was the best compromise $$ wise and this also allows us to set the geo at a lower temp than the wood burner. So if the wood burner were to go unexpectidly go out our house would at least stay x degrees.

I installed a 14" electrically contolled zoning damper that keeps the AC and heat from the geo out of the woodburning furnace.

Thanks,

Scott

P.S What part of Ohio do you live in ? I am about 20 miles north of Cbus. I read in one of your other posts that you work on computers. That is what I do for a living also. Small world.

 

[laynes69]

Columbus is about 1 hour south of here. I work on computers here and there, I'm a trainer for a laboratory. Don't know if I'd have the patience for full time computer repair lol. I would put a backdraft damper in there, not sure how the fan from the geo will work.

 

[Fyrebug]

Laynes,

Thanks for the information. I wish PSG would include that information in the manual.

I am planning on firing up the furnace up next week so I will see how it draws.

Thanks,

Scott

Which information would you like us to include? The manual is quite specific on this matter but if there is a better way to do it, please let me know and we'll make the changes. Right now this is what is says...

If draft exceed –0.06 in. W.C a barometric damper should be installed on the smoke pipe.

Never install a manual damper.

The barometric control must be adjusted so that the maximum draft measured at the furnace outlet does not exceed -0.06 in. w.c. Please note that a draft exceeding -0.06 in. w.c. will reduce the efficiency and could produce an uncontrollable fire. On the other hand, the minimum draft required is -0.04 in. w.c. in the evacuation pipe on the wood side, no matter what type of furnace (WOOD, WOOD / ELECTRIC OR WOOD / OIL).

 

[Fyrebug]

Fyrebug,

I believe the existing plenum is 8" or 9" tall. The pipe coming out of the top of the PSG plenum is 14" which is rated for 700CFM. I do not have a manometer to measure water column. I do have a friend who is a commercial HVAC tech and I am sure he has one.

What should the height of the PSG plenum be ? I could have one built and tie the 14" pipe into the side of it ?

Scott

What you should do is have your friend take the static pressure when the furnace is running and see what your getting.

When furnaces are designed, it goes through extensive testing to ensure maximum efficiencies. The manual is not a 'wish list' but rather specifications to follow to meet the stated performance. Any deviations from it might compromise your performance. As per my previous post, you 'may' encounter issues with your current set up. That's why you should test it first to make sure you meet the static pressures.

If you look on page 6 of the manual, you'll see the recommended plenum size. Let me know how it goes.

Basically, if your take-off is flush with the top of the plenum you can go as low as 18". If your take off is below, then you must allow at least 24" height.

 

[CrappieKeith]

not to bud in but...knowing barometric draft regulators like the ones Field Controls make....the T in the pipe is facing the wrong way for a BDR to be mounted.

As to the other thing of the coil from the pump....you really need to have a back flow damper that will fail closed if the pump blower does not run. For whatever the reason...if the pump blower is not on you couldstart a fire in your ducting that could spread through the home or melt the condensate pan if it is constructed of plastic which most are these days...unless the hvac contractor made it of metal which code says all ducting should be made of metal...including condensate pans when a high heat (wood) appliance is attached.

 

[Fyrebug]

Just to explain why you need more plenum volume in a wood burning furnace.

Static pressure basically acts like a damper. If you have too much air flow ('damper' fully open) past the exchanger, the air does not have time to pick up enough heat. It also cools down the fire box too fast and affects your efficiencies and may cause condensation (creosote).

If you have too much static pressure ('damper' is closed or partway closed) heat builds up within the unit. This causes a few problems. 1) your furnace was not designed to operate beyond certain temps. You may shorten the life of the furnace or its components 2) If the power goes out, the fire does not. Under this condition, you no longer have a blower to cool down and recuperate the heat. You may end up with a massive heat build up which again may damage your furnace.

That is why it is good to always follow the MFG recommendations.

 

[morningwood]

Thanks for all of the replies. Sorry it took me awhile to get back to you guys but I have spent the last few days painting and chasing / hauling Amish around.

I fired up the furnace a few days ago for a few hours. Then yesterday for about 6 hours. I will say the furnace is pretty impressive even with my hokey setup. I was able to easily keep the house ( pretty well insulated 2200 sq ft ranch ) when the temps outside were around 30F with only three pieces of split maple in the firebox. I looked outside at the stove pipe a few times and could hardly see any smoke coming out. My last stove had a catalytic converter, so not having to deal with that and being able to have high efficiency is a win-win for me. :msp_biggrin:

Fyrebug,

I talked to my HVAC friend and he said next time he is in the area he will let me borrow his menometer or stop over and take a pressure reading for me.

I am not sure why the HVAC contractor did not build the wood burning furnace plenum to the recomended size. I gave him the owners manual so he could get the correct information. $$$ I would say is probably the driving factor.

As time permits I will send you a PM with some of the issues that I found with the owner's manual. I have written my fare share of documentation so I know how hard it is write.

Thanks,

Scott

 

[morningwood]

CrappieKeith,

All of the HVAC piping is metal except for hot / cold air returns that are in the crawl space underneath the house. These are insulated metal flex duct. We used these since they are in a unconditioned space. The flex duct is rated for propane / gas furnaces which can produce temps of 150F.

I agree that running the geo fan is not the best solution since if it does go out I could possibly ruin the coil on the geo unit. I found a anti backdraft damper that will fit the geo plenum. As the $$$ become available I am going to invest in one.

Thanks,

Scott