Negative pressure in house after winterizing

[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.

 

[OmCheeto]

That's pretty good!

Yay!

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

I'm going to go out on a limb here, and call this "radon destroyer" device a "non-significant" variable.

My guess as to the "most significant variable" would be: Fireplace maximum BTU/hr output...

This would lead to an inferred minimum opening for your chimney flue damper.

 

[Greg Bernhardt]

This would lead to an inferred minimum opening for your chimney flue damper.

The damper is pinned open about an inch.

 

[Bystander]

I'm going to go out on a limb here, and call this "radon destroyer" device a "non-significant" variable.

..., so long as it was "proper retrofitting." How many cracks in the basement floor?

 

[Greg Bernhardt]

..., so long as it was "proper retrofitting." How many cracks in the basement floor?

None, it was sealed with epoxy paint a few years ago

 

[Bystander]

None, it was sealed with epoxy paint a few years ago

Including all water, sewer, gas line, et cetera, ... "hokay."

 

[NTL2009]

The damper is pinned open about an inch.

Seems that would be sucking air from that floor, and that would also draw air from the attic door, causing the plastic to be sucked into the room.

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.

I'd expect the water heater has a powered vent, that is typical of a through-the-wall exhaust. Probably PVC?

 

[Nik_2213]

Does the effect vary with wind direction ? Along vs across the ridge-line ?? Or relative to any eave gaps ?? Harking back to something I read long ago on storm resistance, specifically venting 'attic pressure' lest it help remove your roof, I'm thinking 'aerodynamics'...

 

[matt621]

My opinion: Everything in the house creates heat. People, stove, water boiler, oven, TV, etc. That has to go someplace. So it's found a way out. Chimney, holes for the lights, wall outlets, door jams etc. That creates a current of air that is creating an negative (with relation to outside) vacuum. So the air is trying to come by the windows to equalize the house pressure.I found this out when I put a cooler in the attic. I had an evap cooler in the attic and it did a great job. Problem was it also pushed all the humid air into the house. It took me years to patch all the air gaps and there were hundreds. I've got it pretty close now, but there is a still a slight breeze when the cooler is running. (Enough to push a door closed to the garage if it's slightly ajar. Before I did all the patching and plugging it would slam that same door closed!) Your case is the opposite, but it's still probably the same thing. And as others have said any course of heat that burn something has to pull it's air from someplace. But even if you had them all vented with their own intakes, you, your TV, your stove, etc being in the house will generate heat that is trying to find a way out. Once it does, you create the vacuum you are seeing.

Once you plug all those leaks you'll probably see positive pressure in the house.

HTH

 

[Greg Bernhardt]

Small update: I found evidence of mice in my basement but couldn't figure out where they were coming in from. Then I crawled under my deck which has very low clearance and saw there is essentially a missing brick in the lower outside wall. Obviously that is how they are getting in and I wonder if that hole was contributing to my pressure issue. I mean literally there is a brick size hole leading into my basement. I never saw it from the inside because there is dry wall down there.

 

[Nik_2213]

Well spotted ! Was there an old pipe or something before ?
Whatever, at this time of year, expanding foam is your friend...

 

[Greg Bernhardt]

Well spotted ! Was there an old pipe or something before ?
Whatever, at this time of year, expanding foam is your friend...

No it appears to just have just crumbled away. God knows how many years it's been like that! Should be above 40F on tuesday which is apparently required for foam or mortar. I was thinking of just doing it right with mortar instead of using foam. I've heard mice can chew through it. Will be awkward though since the clearance is like 12in

 

[jim hardy]

I'm a fan of mortar. You might toss in a few handfuls of Portland to make it stronger.

There's a product called "Hydraulic Cement" that sets up in about five minutes and gets hot to the touch. I used it around my septic tank entrance, it's amazing stuff.
You could use it like mortar . Get a bucketful of stones and build a mini rock wall where that missing brick is.
Mix just a little at a time, though.

 

[nitsuj]

Does the effect vary with wind direction ? Along vs across the ridge-line ?? Or relative to any eave gaps ?? Harking back to something I read long ago on storm resistance, specifically venting 'attic pressure' lest it help remove your roof, I'm thinking 'aerodynamics'...

I think it's probably ghosts, I don;t understand how with higher temp inside than out that there could be lower pressure through out the house when nothing is on...of course presuming it's not the weather outside it must be ghosts right?

 

[Greg Bernhardt]

We are having a windy day with gusts of 60mph. What I'm noticing is that our two bathroom fan vents are drafting some cold air. Both exhausts to the outside have flaps, but perhaps they aren't effective enough. Are there brands where the seal is tight? This seems like an obvious huge heat drain.

 

[OmCheeto]

...windy day with gusts of 60mph...

hmmm... Cold weather + wind + reality = "Homework problem template", IMHO.

One thing I know: Air has a very low heat capacity.

Until we determine the:

1. surface volume of your house
2. its R-value, and
3. the mass or volumetric flow rate of your vents

we can't really determine if it's obvious.

 

[russ_watters]

We are having a windy day with gusts of 60mph. What I'm noticing is that our two bathroom fan vents are drafting some cold air. Both exhausts to the outside have flaps, but perhaps they aren't effective enough. Are there brands where the seal is tight? This seems like an obvious huge heat drain.

The technical name for what you want is a "backseat damper". The fan itself probably has a gravity closed but unsealed plastic flap. If it isn't doing the job for whatever reason, you can buy a better one (metal, sealed, balanced and spring loaded) at Home Depot, connect it to the existing duct with zip ties and break the plastic one off.

 

[russ_watters]

hmmm... Cold weather + wind + reality = "Homework problem template", IMHO.

One thing I know: Air has a very low heat capacity.

Until we determine the:

1. surface volume of your house
2. its R-value, and
3. the mass or volumetric flow rate of your vents

we can't really determine if it's obvious.

With an unsincere apology to SI adherents, a standard residential exhaust fan is 50 CFM and air has a heat capacity of 1.08 BTU/hr/cfm. Let's guess 10% leakage on average and a 30F average winter outdoor temperature (70F room temp). That's 216 BTU/hr. Gas costs something like $6 per million BTU so at 80% efficiency for his boiler, that's $1.17 per month of lost energy. If he can save that 3 months of the year (not including summer savings as well...) and do the install himself with an $11 part, it'll pay back in 3 years.

Not sure what you were after with R-Value, but Greg is asking about direct air leakage...

 

[Greg Bernhardt]

The technical name for what you want is a "backseat damper". The fan itself probably has a gravity closed but unsealed plastic flap. If it isn't doing the job for whatever reason, you can buy a better one (metal, sealed, balanced and spring loaded) at Home Depot, connect it to the existing duct with zip ties and break the plastic one off.

Maybe I need a better outside vent?
https://www.amazon.com/dp/B004VZ2XT6/?tag=pfamazon01-20

Or are you talking more like this?
https://www.houzz.com/product/41883...st-ducts-4-contemporary-bathroom-exhaust-fans

Or both? Problem is my upstairs bath fan is vented through the roof. I don't really want to go up there.

 

[gmax137]

air has a heat capacity of 1.08 BTU/hr/cfm

? I think heat capacity needs a temperature dimension in the units

 

[russ_watters]

Maybe I need a better outside vent?
https://www.amazon.com/dp/B004VZ2XT6/?tag=pfamazon01-20

Or are you talking more like this?
https://www.houzz.com/product/41883...st-ducts-4-contemporary-bathroom-exhaust-fans

Or both? Problem is my upstairs bath fan is vented through the roof. I don't really want to go up there.

I was referring to this:
https://www.homedepot.com/p/VENTS-U...gclsrc=aw.ds&dclid=CPC2952b9tcCFei4swodPecDaQ

If you have a side discharge you might try replacing the whole hood/damper unit.

That was for a dryer though an I was thinking your damper might be on the fan. That's common: