Negative pressure in house after winterizing

[Greg Bernhardt]

I sealed my attic door and a set of 3 old windows downstairs with plastic. When everything else is closed up the two sets of plastic become extremely tight and you can see/feel the pressure pushing the plastic into the house. Almost to the point of ripping the tape off holding the plastic. Today was a nice day so I opened a downstairs door and as expected the pressure on the plastic was just about gone. So the question is how do I shore up these two massive air exchange areas but not create a negative pressure issue, which I assume is causing issues elsewhere.

 

[OmCheeto]

What's the difference in plastic "tightness" when your furnace is running compared to when it's not running?

 

[Greg Bernhardt]

What's the difference in plastic "tightness" when your furnace is running compared to when it's not running?

I have a water boiler and rad setup.

 

[russ_watters]

I have a water boiler and rad setup.

Same question applies. Or, to expand: does the boiler use outside air for combustion air (via a duct next to or concentric with the exhaust) or does it pull air in room air from the basement or wherever it is located?

Also, do you notice a difference with bathroom exhaust fans on or off?

If it isn't fans, then it is probably stack effect. Are there any significant penetrations between your upper floor ceiling and attic? Can they be sealed better? May include: light fixture cutouts, power outlet and light switch cutouts (can buy gasketed covers), attic stair hatch, whole house fan louver.

 

[OmCheeto]

I have a water boiler and rad setup.

Coal fired boiler?

 

[Greg Bernhardt]

Coal fired boiler?

gas

 

[OmCheeto]

gas

Model number?

 

[Greg Bernhardt]

Same question applies. Or, to expand: does the boiler use outside air for combustion air (via a duct next to or concentric with the exhaust) or does it pull air in room air from the basement or wherever it is located?

Also, do you notice a difference with bathroom exhaust fans on or off?

If it isn't fans, then it is probably stack effect. Are there any significant penetrations between your upper floor ceiling and attic? Can they be sealed better? May include: light fixture cutouts, power outlet and light switch cutouts (can buy gasketed covers), attic stair hatch, whole house fan louver.

I think it must use the chimney. The fans don't seem to make a difference. There doesn't seem to be any openings or gaps to the attic other than the door. I guess light fixtures though. The windows are on the 1st floor btw. Does that make a difference in stack effect? In any case if stack effect should the attic plastic be pushing out instead of in?

 

[russ_watters]

I think it must use the chimney.

Is there a metal duct going into the chimney (and sealed around it) or do you just have a wide open chiney opening into your basement? A wide open chimney could cause this: do you feel cold air dumping down out of it?

There doesn't seem to be any openings or gaps to the attic other than the door. I guess light fixtures though. The windows are on the 1st floor btw. Does that make a difference in stack effect? In any case if stack effect should the attic plastic be pushing out instead of in?

Stack effect is when the warm, less dense air inside your house forces its way out the top of your house, to be replaced by cold air forcing its way in in the bottom. So the inward suction would be visible in the entire envelope, but worse the lower you get.

Is your attic finished and heated and relatively tight? Semi-finished but unheated and not very tight? Or unfinished and intentionally open to outdoors?

Either way, sealing around the attic door might help a lot. You might try feeling around the door from above to see if you can feel warm air from the house going up into the attic. You can use a tissue to find soft air movement. Or better yet an infrared temperature gun or camera to identify where air is going in/out.

 

[Tom.G]

does the boiler use outside air for combustion air (via a duct next to or concentric with the exhaust) or does it pull air in room air from the basement or wherever it is located?

That's the most likely, the heating system using indoor air for combustion. Normal in older houses. Even when it's not combusting, you get to contend with the stack effect.

Try the tissue test that @Russ watters suggested around the boiler and/or the room it is in. Do it with an outdoor window or door open for maximum airflow. If you don't mind playing with fire, a candle works, and so does some newspaper tightly rolled/crumpled, ignited, then blown out; it smolders for quite some time with lots of smoke. Being easy to see and track, the newspaper smoke is good for large-area surveillance without trying to keep a candle lit!

EDIT: If it is indoor combustion air being used, install a duct to use outdoor air. It will probably pay for itself in one heating season; especially in snow country.

 

[jim mcnamara]

EDIT: If it is indoor combustion air being used, install a duct to use outdoor air. It will probably pay for itself in one heating season; especially in snow country.

@Tom.G or @russ_watters
...not had enough coffee yet. Assuming this is because convection is moving air in both directions (up/down) the chimney, essentially sucking in cold air.
And heating the outside. Akin to the reason you keep a damper in a fireplace closed when not using the fireplace. I tried to look up a link for convective loss from heating systems and heat energy contribution to urban heat islands. Found none, or I messed up somehow.
Edit:
Found items like this - mostly mentioning effects of using AC, a secondary source of heat, nothing about wintertime convective heat loss - https://www.epa.gov/sites/production/files/2014-06/.../basicscompendium.pdf

 

[russ_watters]

Some links:

http://www.greenbuildingadvisor.com/stack-effect-when-buildings-act-chimneys

http://www.myhomescience.com/understanding-stack-effect/

https://www.angieslist.com/articles/seal-your-home-prevent-stack-effect.htm

Cutouts for light fixtures and receptacles are a surprisingly significant part of the problem.

 

[Greg Bernhardt]

Today I woke up and the plastic ripped the tape off the window frame. Something I should maybe note is that currently my boiler is not running and the outside air is only a few degrees cooler than inside during the day and maybe 10 degree different at night.

Model number?

Utica Boiler Type B Vent Model MGB125HID

Is there a metal duct going into the chimney (and sealed around it) or do you just have a wide open chiney opening into your basement? A wide open chimney could cause this: do you feel cold air dumping down out of it?

Yes there is metal duct going into the chimney. Something that may be relevant, is I have gas log fireplace with a pilot light so they fixed the damper slightly open to vent.

Stack effect is when the warm, less dense air inside your house forces its way out the top of your house, to be replaced by cold air forcing its way in in the bottom. So the inward suction would be visible in the entire envelope, but worse the lower you get.

If it were the stack effect wouldn't the 1st floor plastic over windows feel inward pressure but the 2nd floor attic door (regular door) plastic should feel outward pressure? However both experience inward pressure.

Is your attic finished and heated and relatively tight? Semi-finished but unheated and not very tight? Or unfinished and intentionally open to outdoors?

Attic is not finished at all other than it's original wood floor, which is why I seal it. Almost no insulation.

Either way, sealing around the attic door might help a lot. You might try feeling around the door from above to see if you can feel warm air from the house going up into the attic. You can use a tissue to find soft air movement. Or better yet an infrared temperature gun or camera to identify where air is going in/out.

The attic door is sealed with plastic, but perhaps there is still air leakage around the bottom where the floor is. I have wood floors and certainly there are cracks. Maybe air is leaking through the cracks near where I tape the plastic down and going under the floor.

That's the most likely, the heating system using indoor air for combustion. Normal in older houses. Even when it's not combusting, you get to contend with the stack effect.

Looks like it uses indoor air and vents into the chimney. However, like I said, the boiler isn't even on at the moment.

 

[jim mcnamara]

However, like I said, the boiler isn't even on at the moment.

Yes, but the air flow access to chimney is not dampered shut?

 

[jackwhirl]

Stack effect is when the warm, less dense air inside your house forces its way out the top of your house, to be replaced by cold air forcing its way in in the bottom. So the inward suction would be visible in the entire envelope, but worse the lower you get.

If it were the stack effect wouldn't the 1st floor plastic over windows feel inward pressure but the 2nd floor attic door (regular door) plastic should feel outward pressure? However both experience inward pressure.

Does the pressure come and go with the wind? I experienced something very similar last winter and it was just a lot of infiltration (very drafty sliding porch door). I think you're likely going to have to settle for more/better tape or some sort of mechanical solution.

 

[Greg Bernhardt]

Yes, but the air flow access to chimney is not dampered shut?

I'm a little uncertain about the internal structure of the chimney because in the basement obviously the boiler is vented into the chimney but on the first floor there is a fireplace, so obviously there must be a double chamber that meets together further up at some point? I know the fireplace damper is pinned a little open to vent the gas logs.

Does the pressure come and go with the wind? I experienced something very similar last winter and it was just a lot of infiltration (very drafty sliding porch door). I think you're likely going to have to settle for more/better tape or some sort of mechanical solution.

Wind makes no noticeable difference at least the past few days since putting up the plastic, there is been little wind.

 

[Nidum]

Fit a spoiler valve ? Flap of plastic over a hole would do the job .

 

[Greg Bernhardt]

Fit a spoiler valve ? Flap of plastic over a hole would do the job .

What is this in reference to? :)

 

[OmCheeto]

So basically, you have 100 years worth of technology, all duct taped together.
Interesting problem.

My somewhat naive answer, as I doubt there is an off the shelf solution to this problem, to your question:

So the question is how do I shore up these two massive air exchange areas but not create a negative pressure issue, which I assume is causing issues elsewhere.

would be to install a vent into your basement.

As far as I can tell, the design of your house, and your two heat sources, are acting like a vacuum cleaner, with your hand over the end of your intake hose.
Everything is trying to suck air out of your house, and there's no place for air to come in, so, you've created a vacuum.

ps. MBH = 1000 BTU/hr
Lots of unfamiliar acronyms in the pdf for your furnace.

 

[Greg Bernhardt]

As far as I can tell, the design of your house, and your two heat sources, are acting like a vacuum cleaner, with your hand over the end of your intake hose.
Everything is trying to suck air out of your house, and there's no place for air to come in, so, you've created a vacuum.

That makes sense for when they are on, but this is happening but the boiler nor fireplace (outside of pilot light) is on.

 

[OmCheeto]

That makes sense for when they are on, but this is happening but the boiler nor fireplace (outside of pilot light) is on.

In that case, I would research Russ's suggestion:

If it isn't fans, then it is probably stack effect.

Since I live in a single story house, with no basement, I'm afraid I can't do the experiments for you, to determine if this is the cause.

ps. Houses have lots of variables, and make for some of the best thermodynamic experiments ever.

 

[Greg Bernhardt]

In that case, I would research Russ's suggestion:

But if it was stack effect why would the attic door plastic be pushing inward. Wouldn't it push outward from the warmer inside air?

 

[OmCheeto]

But if it was stack effect why would the attic door plastic be pushing inward. Wouldn't it push outward from the warmer inside air?

As I said; "lots of variables".
I'm guessing, that like most houses, your attic is not air tightish, while the rest of your house, is.
Hence, your attic is basically an outside air source.

ps. DO NOT try and air seal your attic. I did that last winter, forgot about it, and created a roof destroying sauna this last spring. Fortunately, I discovered the sauna before my roof collapsed.

 

[Greg Bernhardt]

Hence, your attic is basically an outside air source.

Indeed, which why I need to seal the door because cold air rushes down.

 

[OmCheeto]

Indeed, which why I need to seal the door because cold air rushes down.

But if you solve the attic air problem, your two downstair window problems will get worse.
And if you solve those, then your house will become too air tight, and your furnace may kill you.

 

[Greg Bernhardt]

But if you solve the attic air problem, your two downstair window problems will get worse.
And if you solve those, then your house will become too air tight, and your furnace may kill you.

So pretty much I should stop wasting my time and just deal with the energy bill?

 

[Tom.G]

Indeed, which why I need to seal the door because cold air rushes down.

So pretty much I should stop wasting my time and just deal with the energy bill?

No! you need to find where the air is exiting. When you find that you can decide what the most appropriate fix is; be it sealing some leaks or giving an alternate source to the exit point.

But if it was stack effect why would the attic door plastic be pushing inward. Wouldn't it push outward from the warmer inside air?

The stack effect is driven by both altitude difference and temperature difference. So the distance between the lowest chimney opening (probably the boiler burner) and the top of the chimney is relevant. Here is a calculator to give you an idea of the flow rate.
https://www.chimneysheep.co.uk/how-to-use/stack-effect-calculator/

And here is a more detailed calculator to find flow rate, velocity, and pressure difference.
https://www.engineeringtoolbox.com/natural-draught-ventilation-d_122.html

Don't give up before the root cause is located, it's not rocket science, just a bit of sleuthing. (unless, of course, you have money to burn. )

 

[Nidum]

Spoiler valve (in this case) = improvised self acting excess pressure difference release valve .

A simple device which is closed most of the time but which opens occasionally to prevents the pressure difference between attic and either outside or lower part of house from getting too great .

Means that your sealing up remains effective but problems of pressure difference causing possible damage are eliminated .

 

[OmCheeto]

Spoiler valve (in this case) = improvised self acting excess pressure difference release valve .

A simple device which is closed most of the time but which opens occasionally to prevents the pressure difference between attic and either outside or lower part of house from getting too great .

I've reread the thread a couple of times, looking for things I might have missed, and I found one:

(outside of pilot light) is on.

I think this precludes sealing the chimney up tight, based on what I found out about pilot lights: "You need to understand that most Gas Fireplaces have pilot’s which use about 900-1100 BTU/hr." [ref]

Doing a bit of maths, as I have no sense of what a BTU/hr is:
1000 BTU/hr = 16.7 BTU/min = 293 watts

So, about an hour ago, I stuck a 250 watt heating lamp into my wood stove, along with a temperature detector.
I shut the flue damper, and the front doors, and the flue temperature rose from ambient (67°F) to 98°F.

My conclusion was, that I still don't know enough about Greg's setup to make a conclusion.
His flue damper is probably[?] set up such that his chimney can vent via natural convection.

@Greg Bernhardt , do you have the model number of your "gas log fireplace" thingy?
Wondering if it's glass covered or open.

ps. Anyone know how flame angle corresponds to wind speed? I googled it, and couldn't find anything. (Google asked; "Do you mean 'candle flame angel?" To which I thought, but could not respond; "No! I'm not looking for higher powers to answer my question, you IDIOT machine!")

Anyways, after temperatures stabilized, I removed the heat source, and opened everything wide open.
I put a candle in front of the opening, and the flame angle appeared to be at ≈45°.

From which I determined: Stack effect is real.

 

[256bits]

and the flame angle appeared to be at ≈45°.

Remarkable.
To find the wind speed we could

Rather than calling up NASA to acquire access to their wind tunnel and supercomputer in order to solve the Navier Stokes equation and model testing, which might takes weeks, we could pick up the candle and walk with it, all the while recording our walking speed and flame angle.
My test came to 1 foot/sec velocity, with a xmas candle.
A very slow walk.
Of course, the experiment should be repeatable and verified by independent sources.
I am not sure if Feynman would have actually done that, if not, then Galileo.

 

[Evo]

Maybe this blog will help? They seem to be touting this "blower door" testing, but maybe the other information will be helpful.

https://www.energyvanguard.com/blog/53609/The-3-Rules-of-Air-Leakage-Plus-a-Bonus

another link https://www.energyvanguard.com/diagnostic-performance-testing/airtightness-blower-door

https://www.energyvanguard.com/blog/33369/Hidden-Air-Leakage-Sites-in-Your-Attic

 

[Greg Bernhardt]

Wondering if it's glass covered or open.

Open. In the end by sealing up everything else, it could cause the chimney to back-draft right? I do have carbon monoxide detectors on each floor.

 

[OmCheeto]

Open. In the end by sealing up everything else, it could cause the chimney to back-draft right? I do have carbon monoxide detectors on each floor.

That was my worry. But I have a friend with a natural gas fire place log thingy, and it vents INTO the house. I didn't really look into it until yesterday as to how they work, without killing the occupants:

ventless-fireplaces-what-you-need-know

...These safety devices automatically shut off the fireplace if the carbon monoxide level in the room rises above 25 parts per million, and/or the oxygen level falls below 18%...​

[ref]​

Looking through the manual for your boiler, it appears to have a powered damper(page 13), so I think we can eliminate that as a problem, when it's not in operation.

The instructions also mention, on page 6, that exterior air needs to be supplied.
One of several options mentioned:

Mechanical Air Supply. Provide minimum of 0.35 cfm per Mbh for all appliances located within space.
Additional requirements where exhaust fans installed.
Interlock each appliance to mechanical air supply system to prevent main burner operation when mechanical air supply system not operating.​

Unfortunately, I doubt your gas fireplace has such an interlock.
And it also sounds like most of your house is very well sealed.

If I were you, I'd add an intake duct adjacent to the fireplace intake.
Not sure if this is feasible.
If not, you might try leaving the door to the basement open, and see if that stops the attic door, and downstairs window drafts.

btw, did you ever find the model number for your fireplace?

 

[OCR]

Anyone know how flame angle corresponds to wind speed? I googled it, and couldn't find anything.

I'm not looking for higher powers to answer my question...

I must take strong exception to your assessment of my ability to answer questions... I will, however, offer some gentle guidance.

Consequently, of course, you must independently... determine the relevance . .

 

[OmCheeto]

I must take strong exception to your assessment of my ability to answer questions... I will, however, offer some gentle guidance.

Consequently, of course, you must independently... determine the relevance . .

It would appear that "candle" is the culprit for summoning wannabe deities.

Looking at the sources in your google search, I've decided flame angle is too complicated, and I'm going to ignore it.

But back to the problem.
@Greg Bernhardt , do you have a gas fired water heater hooked up as shown in your boiler manual(page 13)?

God knows, we need another variable here...

 

[Greg Bernhardt]

@Greg Bernhardt , do you have a gas fired water heater hooked up as shown in your boiler manual(page 13)?

Water heater is vented directly outside through basement wall. I have a humidifier running in the basement but that just cycles inside air right?

 

[OmCheeto]

Water heater is vented directly outside through basement wall. I have a humidifier running in the basement but that just cycles inside air right?

I would think so.

So, did we ever determine if you have an outside air source to your basement?
The water heater is going to be drawing air into your house.
So, although it may not be adding to the "stack effect" of your chimney, it's definitely a pertinent variable.

[edit: I think we can ignore the humidifier as a variable in this problem. Not to say that humidity levels aren't a problem, but that's another thread, IMHO.]

 

[dlgoff]

... question is how do I shore up these two massive air exchange areas but not create a negative pressure issue, ...

from https://fixhomeenergy.com/2010/11/02/solution-basics-pressure-balancing/

Ideally, the pressure difference between inside and out is near zero, just like it is with an air leaky house. Mechanical ventilation works well only when there is a pressure difference between inside and out. Therefore, it’s unrealistic to expect a tight house be at neutral pressure with respect to outside at all times.

bold by me

 

[russ_watters]

But if it was stack effect why would the attic door plastic be pushing inward. Wouldn't it push outward from the warmer inside air?

Maybe. In a perfect stack all the air goes out the top and in the sides. In a house that has a tight enough roof, it might go out the top floor. But it is tough to know.

The air has to be coming from somewhere though, and there are only a few possibilities; fan forced, stack effect and wind are pretty much it.

 

[Tom.G]

The air has to be coming from somewhere though

It is trying to come from the great outdoors. Assuming there is not a continuous wind blowing on those plastic sheets, the question is where is it leaving to create the partial vacuum?

p.s. Incense sticks also create enough smoke to help track the air movement.

 

[russ_watters]

It is trying to come from the great outdoors. Assuming there is not a continuous wind blowing on those plastic sheets, the question is where is it leaving to create the partial vacuum?

p.s. Incense sticks also create enough smoke to help track the air movement.

Yes, I said the problem backwards.

 

[Dr. Courtney]

My bet is on the stack effect. Does it seem more pronounced on sunny days than on overcast days or on cooler nights? That would seem to support the stack effect.

 

[Greg Bernhardt]

My bet is on the stack effect. Does it seem more pronounced on sunny days than on overcast days or on cooler nights? That would seem to support the stack effect.

But again wouldn't that make the plastic on the attic door push outwards?

Something else I just thought of was that I have a radon exhaust fan but the pipe goes from the basement floor (sealed) to the outside.

 

[Dr. Courtney]

But again wouldn't that make the plastic on the attic door push outwards?

Something else I just thought of was that I have a radon exhaust fan but the pipe goes from the basement floor (sealed) to the outside.

The typical flow in the smokestack effect is inflow at the lower levels and outflow at the higher levels, but there can be other things going on.

Hard to be sure with limited information. The house I am picturing in my mind is like older homes we lived in in the NE, but the actual home in question might be much, much different.

 

[Bystander]

(sealed)

Whole new ball game.

 

[WWGD]

Good deal, I read this before having my coffee: " Negative Pleasure in the Attic". Wow, this Greg is into pretty cool, avant-garde stuff. That one I could try to answer, but I can't help with the negative pressure one, sorry.

 

[Greg Bernhardt]

Whole new ball game.

From what I can see it takes air from under the house and sends it outside.

 

[OmCheeto]

From what I can see it takes air from under the house and sends it outside.

Is the following close to an accurate doodle of your house?:

By "under the house", do you mean "basement"?

ps. I think the mentors should all conspire to threaten to resign unless you start using the "Homework template" with these problems...

Homework Statement

Problem: The pressure in my living area is less than in the attic and outside. Why is that?
Variables: Boiler, water heater, and radon gas extractor are in the basement. Fireplace is in the living area.
Data:

Chimney cross sectional area is: ?
Chimney height is: ?
Fireplace maximum BTU/hr output is: ?
Fireplace idle BTU/hr output is: 1000
Boiler maximum output is: 125,000 BTU/hr
Radon gas extractor flow rate is: ?
Fan supplying outside air to basement flow rate is: ?​

Homework Equations

Not a clue.

The Attempt at a Solution

I don't know where to begin.

 

[Greg Bernhardt]

Is the following close to an accurate doodle of your house?:

That's pretty good!

By "under the house", do you mean "basement"?

The pipe goes into the basement floor and sucks air from under the basement floor

 

[jim hardy]

Is the following close to an accurate doodle of your house?:

I hope the water heater vent goes clear up to the roof - else taller chimney draft can overwhelm it and suck combustion products in backward.