negative pressure issues

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.
BLIMP said:
any exterior chimney is a poor drafter & the house itself has a chimney effect but if u can crack a window near the fireplace & it works then...
if u had a neg. pressure prob i'd guess your cellar fireplace would stink during the summer when vents are running & windows aint open?
FYI= old wisdom sez NEVER TRY TO HEAT A HOUSE FROM THE S SIDE , this is because the prevalent N winds of winter result in N-S airflow in a house.
u have complicated scenario though interesting

the fireplace never stinks during the summer unless i run the whole house fan with out enough windows open
my house pretty much faces north.. the large over hang was to allow for thermal heating in the winter and cooling in the summer .. my stove (summit) are all in the house facing east .. same as my fireplace in the basement.. the pellet stove is on the east side of the house pointing west?

so do you think cracking the windows will solve it? and how will that effect the temp of the house.. in the winter

dont know if it matters but my chimney is interior not exterior.. could that be adding to the problem?
 
Semipro said:
Can you get make-up air from the roof? I once had a direct vent gas stove that pulled air from a rooftop fitting and exhausted there also.

can you post a link that would prolly help me alot
 
iceman said:
BLIMP said:
any exterior chimney is a poor drafter & the house itself has a chimney effect but if u can crack a window near the fireplace & it works then...
if u had a neg. pressure prob i'd guess your cellar fireplace would stink during the summer when vents are running & windows aint open?
FYI= old wisdom sez NEVER TRY TO HEAT A HOUSE FROM THE S SIDE , this is because the prevalent N winds of winter result in N-S airflow in a house.
u have complicated scenario though interesting

the fireplace never stinks during the summer unless i run the whole house fan with out enough windows open
my house pretty much faces north.. the large over hang was to allow for thermal heating in the winter and cooling in the summer .. my stove (summit) are all in the house facing east .. same as my fireplace in the basement.. the pellet stove is on the east side of the house pointing west?

so do you think cracking the windows will solve it? and how will that effect the temp of the house.. in the winter

dont know if it matters but my chimney is interior not exterior.. could that be adding to the problem?
my bad! u got interior chimney which does have a lot of mass above the roof which stays cold with the weather so insulated liner would help fireplace? I'd try cracking window in cellar when fp is smoking just to see if prob is solved, be4 making holes in the house
 
BLIMP said:
iceman said:
BLIMP said:
any exterior chimney is a poor drafter & the house itself has a chimney effect but if u can crack a window near the fireplace & it works then...
if u had a neg. pressure prob i'd guess your cellar fireplace would stink during the summer when vents are running & windows aint open?
FYI= old wisdom sez NEVER TRY TO HEAT A HOUSE FROM THE S SIDE , this is because the prevalent N winds of winter result in N-S airflow in a house.
u have complicated scenario though interesting

the fireplace never stinks during the summer unless i run the whole house fan with out enough windows open
my house pretty much faces north.. the large over hang was to allow for thermal heating in the winter and cooling in the summer .. my stove (summit) are all in the house facing east .. same as my fireplace in the basement.. the pellet stove is on the east side of the house pointing west?

so do you think cracking the windows will solve it? and how will that effect the temp of the house.. in the winter

dont know if it matters but my chimney is interior not exterior.. could that be adding to the problem?
my bad! u got interior chimney which does have a lot of mass above the roof which stays cold with the weather so insulated liner would help fireplace? I'd try cracking window in cellar when fp is smoking just to see if prob is solved, be4 making holes in the house


you can put a liner in an open fireplace??????
 
No liner for open fireplace. Are all of the flues terminating at approximately the same height in this big chimney?
 
iceman said:
BeGreen said:
What is curious is that you feel air flow when the system is off. That's why I asked about make up air. Normally an hvac system is a closed loop. If the power is off to the system, there is normally no airflow.

The house definitely sounds like it is experiencing the stack effect. Is there a whole house vent or attic fan? Are there an upstairs window open? Are there a lot of unsealed recessed ceiling cans in some rooms?

whole house fan yes... but i fill it with insulation (up in the attic) and cover the front with shrink plastic.... upstairs windows are closed... there are some recessed lights that do have the holes in them but should be covered with insulation...
that was my thought before (lights.. ) but if they were sealed wouldnt air still be getting sucked in from somewhere else?
some recessed lights cant be insulated, they specify clearances
 
BeGreen said:
No liner for open fireplace. Are all of the flues terminating at approximately the same height in this big chimney?

yes they are all level with each other ... maybe off by couple inches or less
 
BLIMP said:
iceman said:
BeGreen said:
What is curious is that you feel air flow when the system is off. That's why I asked about make up air. Normally an hvac system is a closed loop. If the power is off to the system, there is normally no airflow.

The house definitely sounds like it is experiencing the stack effect. Is there a whole house vent or attic fan? Are there an upstairs window open? Are there a lot of unsealed recessed ceiling cans in some rooms?

whole house fan yes... but i fill it with insulation (up in the attic) and cover the front with shrink plastic.... upstairs windows are closed... there are some recessed lights that do have the holes in them but should be covered with insulation...
that was my thought before (lights.. ) but if they were sealed wouldnt air still be getting sucked in from somewhere else?
some recessed lights cant be insulated, they specify clearances

these are older ones that have the rating for blown in insulation to be covered
 
iceman said:
BeGreen said:
No liner for open fireplace. Are all of the flues terminating at approximately the same height in this big chimney?

yes they are all level with each other ... maybe off by couple inches or less

I'm not sure it that is root of the issue. It definitely could be in the wintertime. There should be a difference in heights. Here is a quick link to a solution our webmaster came up with: http://www.extendacap.com/main.html

Tom has a pretty good article on the stack effect on his website.

http://www.chimneysweeponline.com/hosmell.htm
 
If there is a problem with the stack effect, it does occur in the summer months but as colder weather hits it gets worse. We have a large 2 story home that suffered horribly with the stack effect in the wintertime and summer. We air sealed our attic and basement and have almost eliminated it. We always had cold drafts. One thing we found that was a big cause of pressure differences in our home was the hvac. You said yours is sealed, ours wasn't. I followed around the home with incense sticks and found alot of stray air paths through the home. If you are having some problems, I would consider having an energy audit done on the home. The can do a blower door test and measure the rate of leakage of the home and find if there are any thermal gaps or bad spots in the home. Here is a link to a good read. Its a larger file, but its worth it.

http://www.efficiencyvermont.com/stella/filelib/TBC_Guide_062507.pdf
 
laynes69 said:
If there is a problem with the stack effect, it does occur in the summer months but as colder weather hits it gets worse. We have a large 2 story home that suffered horribly with the stack effect in the wintertime and summer. We air sealed our attic and basement and have almost eliminated it. We always had cold drafts. One thing we found that was a big cause of pressure differences in our home was the hvac. You said yours is sealed, ours wasn't. I followed around the home with incense sticks and found alot of stray air paths through the home. If you are having some problems, I would consider having an energy audit done on the home. The can do a blower door test and measure the rate of leakage of the home and find if there are any thermal gaps or bad spots in the home. Here is a link to a good read. Its a larger file, but its worth it.

http://www.efficiencyvermont.com/stella/filelib/TBC_Guide_062507.pdf
he's got a built in blower door with the whole house fan= plug the chimneys & do the incense?
 
That would work for a diy test. The reason to have a certified energy audit is they can measure the air loss in a home. They pressurize the house to 50 pascals then do the tests. I believe it simulates a 20 mph wind from all sides of the home. From that point they can tell you yes you have a high or low reading. There are normal places that will allow for alot of air loss. Those being chases that lead from the basement or first floor to the attic, electrical wiring, plumbing, chimneys, etc. Even carrying out tests with the whole house fan would give you ideas on air loss. Wherever you find a leak, caulk it or seal it. Our comfort has been much greater during the winter and summer months.
 
here's a little trick i learned from a rep we have in canada.

if you cannot directly connect an OAK but need makeup air and do not want just an unregulated open hole , make a simple airlock with some PVC and a 5 gallon bucket.

go through the basement wall (aboveground) and insert your PVC (3 inch would be preferrable but 2.5 will still work) after coming in through the wall elbow down and carry the pipe to about 3 inches off the floor INSIDE the 5 gallon bucket.

here's how it works, the negative pressure in the house will pull the air in and being as the air will be colder than the air in the basement the bucket will "trap" it and only allow enough out to satisfy the pressure difference in teh summer it will not trap as much air as the temp differential is not present but in winter when you do not want a big air "leak" the colder it is outside the lesser amount of air is pulled out unless you are running the stoves/fireplaces which increases the draft and pulls more make up air out. it really works.
 
This is very frustrating, some good ideas though... I think I will call for the audit and see what they suggest, for now well until I fet an affordable solution I will be leaving a window cracked, for the pellet stove gonna try to make something to stick in the window and have a 3 inch pipe run from it to the stove since its only about 2-3 ft away.... if it works then in the spring I will run outside air to it through the wall.:.
 
Check with your local electric company. I know around here they offer energy audits for free. I doubt they use the blower door or thermal imaging camera, but even then a good visual inspection will help. If you have fiberglass in the attic, look for dirty spots which will indicate air leakage. Good luck!
 
stoveguy2esw said:
here's a little trick i learned from a rep we have in canada.

if you cannot directly connect an OAK but need makeup air and do not want just an unregulated open hole , make a simple airlock with some PVC and a 5 gallon bucket.

go through the basement wall (aboveground) and insert your PVC (3 inch would be preferrable but 2.5 will still work) after coming in through the wall elbow down and carry the pipe to about 3 inches off the floor INSIDE the 5 gallon bucket.

here's how it works, the negative pressure in the house will pull the air in and being as the air will be colder than the air in the basement the bucket will "trap" it and only allow enough out to satisfy the pressure difference in teh summer it will not trap as much air as the temp differential is not present but in winter when you do not want a big air "leak" the colder it is outside the lesser amount of air is pulled out unless you are running the stoves/fireplaces which increases the draft and pulls more make up air out. it really works.





Been thinking the last couple days and I am gonna try this but I am gonna cut some plywood and do it through a window to see if it helps .... if it works great .. if it doesn't. I will pull out the plywood outta the window... I am gonna do this for the area the pellet stove is in as well!
 
madison said:
Have you considered extending the wood stove chimney to improve draft to overcome the negative pressures? The only reason i suggest that is that the OAK connection to the PE stove is not tight, so you will have cold air entering the room as well....





I think I might be wrong with calling it negative pressure..... it seems that I have so many things running in the winter... it draws air from my air exchanger in the attic... I need make up air...to stop air from trying so hard to get in.... if you go back the first page and see my chimney any modification to it is way to expensive.. due to having so many flues
 
sorry iceman,

i just reread post.

Let me guess, your house is on a slab, and there is ducting and/or a heat exchanger for your HVAC in the attic ("unconditioned space")? I believe I can see the refrigerant lines running up the back of the house from the heat pumps to the attic in one of the pictures....

If yes, I can relate to your issues. The ducting exposed in the attic is typically is not very well insulated maybe R8 at best and will often have holes and leaks where it connects to the heat exchanger, and in the winter, it all gets cold and will create a convection loop and you will feel cold air coming out of the ducts in the lower part of the house.... In our case it is not so much air entering the house, but warm air cycling through the A/C ducting in the cold attic, cooling it off, and pouring out the registers in the lower part of the house as cold air. You may also notice snow melt or frost melt on this section of the roof where the ducting located.

In our case, with only the AC ducting is in the attic (hot water baseboard heat) -- It is a royal pain in the a... , in the fall, I remove and stuff with insulation all of our AIR CONDITIONING registers and AC return ducting. Then remove it in the spring. Of coarse, if your attic ducting is for both Heat and A/C the only option is to wrap and seal the attic ducting and heat exchanger. They do make cardboard boxes that fit over the ducting and then you can fill it with loose insulation to insulate the ducting.

In the future, if possible, I would avoid buying a home with any ducting or heat exchangers in an unconditioned space (attic).
 
madison said:
sorry iceman,

i just reread post.

Let me guess, your house is on a slab, and there is ducting and/or a heat exchanger for your HVAC in the attic ("unconditioned space")? I believe I can see the refrigerant lines running up the back of the house from the heat pumps to the attic in one of the pictures....

If yes, I can relate to your issues. The ducting exposed in the attic is typically is not very well insulated maybe R8 at best and will often have holes and leaks where it connects to the heat exchanger, and in the winter, it all gets cold and will create a convection loop and you will feel cold air coming out of the ducts in the lower part of the house.... In our case it is not so much air entering the house, but warm air cycling through the A/C ducting in the cold attic, cooling it off, and pouring out the registers in the lower part of the house as cold air. You may also notice snow melt or frost melt on this section of the roof where the ducting located.

In our case, with only the AC ducting is in the attic (hot water baseboard heat) -- It is a royal pain in the a... , in the fall, I remove and stuff with insulation all of our AIR CONDITIONING registers and AC return ducting. Then remove it in the spring. Of coarse, if your attic ducting is for both Heat and A/C the only option is to wrap and seal the attic ducting and heat exchanger. They do make cardboard boxes that fit over the ducting and then you can fill it with loose insulation to insulate the ducting.

In the future, if possible, I would avoid buying a home with any ducting or heat exchangers in an unconditioned space (attic).



I never even thought about the loop! Just figured to many things sucking air outta the house so it was pulling from the easiest path...will check to see if return is insulated... if it is its about 20ft away from where the cold air comes in...... could the air turn that cold so quick? Hmmm
 
iceman said:
madison said:
sorry iceman,

i just reread post.

Let me guess, your house is on a slab, and there is ducting and/or a heat exchanger for your HVAC in the attic ("unconditioned space")? I believe I can see the refrigerant lines running up the back of the house from the heat pumps to the attic in one of the pictures....

If yes, I can relate to your issues. The ducting exposed in the attic is typically is not very well insulated maybe R8 at best and will often have holes and leaks where it connects to the heat exchanger, and in the winter, it all gets cold and will create a convection loop and you will feel cold air coming out of the ducts in the lower part of the house.... In our case it is not so much air entering the house, but warm air cycling through the A/C ducting in the cold attic, cooling it off, and pouring out the registers in the lower part of the house as cold air. You may also notice snow melt or frost melt on this section of the roof where the ducting located.

In our case, with only the AC ducting is in the attic (hot water baseboard heat) -- It is a royal pain in the a... , in the fall, I remove and stuff with insulation all of our AIR CONDITIONING registers and AC return ducting. Then remove it in the spring. Of coarse, if your attic ducting is for both Heat and A/C the only option is to wrap and seal the attic ducting and heat exchanger. They do make cardboard boxes that fit over the ducting and then you can fill it with loose insulation to insulate the ducting.

In the future, if possible, I would avoid buying a home with any ducting or heat exchangers in an unconditioned space (attic).



I never even thought about the loop! Just figured to many things sucking air outta the house so it was pulling from the easiest path...will check to see if return is insulated... if it is its about 20ft away from where the cold air comes in...... could the air turn that cold so quick? Hmmm

Yes. Been there. The first winter in our home, we were sitting in the living room and I thought there was an open window. I quickly traced the source to the AC registers. The warm air in the second floor rises into the registers, cools, then the cold air sinks and exits the lower registers. I also noticed snow melt etc on that section of the roof where the A/C system was contained. It can be a rather large source of heat loss from your home, as well as cold air cycling into your home. IMHO, Adding an OAK will not help with this problem.

If you go up into your attic, the myriad of flexible ducting is connected to metal distribution ducts by essentially large tie bands. The connections are not perfect many times, and often get moved. All of this is at best, R8 from what I have read. So you have a huge surface area exposed in your "unconditioned space". The flexible ducts can get poked and torn as well. The metal ducts are crimped together and often very leaky, depending on the quality of the parts and installation. Ours was horrible when I actually went up to look at it.

Typically, the shut offs on the registers are not very airtight and will not really alleviate the problem. I have insulation cut to small squares, remove the registers, insert the insulation, and replace the registers. I also tried, but not very well, to lay insulation on top of the flexible and metal ducting in the attic. They do make a wrap insulation for this purpose, but looks like it would be a pain to do the job.

But this is for the winter , but we only have the air conditioner system in the attic. This helped minimize the leaks and cycling in the winter, but I believe this is generally the nature of HVAC systems that are installed in attics.

If your heat and ac is in the attic, you will have to develop another plan.
 
Status
Not open for further replies.