Last month's gas bill

Re: Last month's gas bill

Lee Dodge wrote: »

Yes, over the last two weeks of December and first two weeks of January we had a large number of nights that had lows between -10 F (-23 C) and -5 F (-21 C), and that spiked the gas usage. My ceiling is R-60, the walls about R-29 (including thermal bridging), while the crawl space walls have R-19 insulation. In addition, this house is fairly well sealed, with a blower door test giving 2.4 air charges per hour (ACH) at 50 Pa differential pressure.

Wow. That's a lot of insulation.

Size of the house matters. Window area is very important. Our house is rather small, but we have several big windows and two patio doors. We have an unheated barn, which is insulated just the same as a house, but there are only very small windows. It never gets colder than -10C, even if it's -40C outside.

Re: Last month's gas bill

ChrisOlson wrote: »

Sealing houses up too tight is what causes condensation - a house that can breathe will not have condensation problems in the attic or walls.

A house that doesn't have insulation doesn't need vapor barrier. That's why poorly insulated houses do not have condensation problems.

If you have a good insulation (such as thick faberglass batts), it will be very cold on one side and very warm on another. When warm air moves through and hits a cold plywood on the other side, all the moisture condenses on it. Things get worse with time because plywood (and much worse OSB) doesn't have pores in it to let the water evaporate to outside.

Once we built a new room in our house and put fiberglass batts between studs. When we came to install vapor barrier two days later, there was a lot of water behind the batts, and in some places up to 1/4 inch ice. Since then, I believe in vapor barrier.

Other example. There was an internal wall in our house and it had a wire coming through 1 inch hole in the top plate. A warm air coming through that relatively small hole was hitting cold roof and caused condensation - there was 3 inch thick ice covering the entire bay between trusses. When it melted in spring, there was water dripping through the soffit. When we closed the hole, there was no problem any more.

Re: Last month's gas bill

ChrisOlson wrote: »

Moisture will condense when you have warm air that can hold more moisture meeting cold air, and the temperature of the warm air reaches the dew point. In winter time it is common in cold climates (where the air is very dry because it can't hold much moisture) to humidify the inside of the house so the RH is around 30-35%. Insulation is nothing but loose fibers that traps air and inhibits its migration from a warm place to a cold place. Over-insulating the ceilings merely causes a stratification where warm air from the living quarters makes a transition to cold air in the attic, and at the point in that stratification where the moisture in the warm air reaches the dew point the water will condense, wet your insulation, reduce its effectiveness, and cause mildew and molds in the insulation. In extreme cases of over-insulating, the insulation will become wet enough to cause water stains in the ceiling, or if there's a vapor barrier the water will collect on top of the barrier and rot the rafters out.

A properly insulated ceiling will let the warm air thru at the proper rate, and leave the attic warm enough, so the water doesn't condense. The roof or attic vents then let the warm moisture laden air out and the water in it condenses where it leaves the attic or roof vents instead of condensing in the attic.

People who live in a cold climate and insulate to ridiculous levels like R60 are doing themselves a disservice, living in a house that is harboring molds in the attic and insulation, and the insulation will become "dusty" from the molds with time. As contractors and HVAC engineers have learned that over-insulating is not good, they have even gone to eliminating the vapor barrier in new construction to allow the building to "breathe" better and prevent the mold problems and mold dust in the attic insulation.
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Chris

You are free to have your own theories, but they are not in agreement with what most building scientists currently think. For example, from GreenBuildingAdvisor.com, "In reality, air leaks mean you’ve lost control of air movement. Air and moisture can be forced into wall and ceiling cavities where water vapor condenses and fosters the growth of mold. Warm air exiting the top of the house can draw in cold air to replace it, wasting heat and energy. In many ways, uncontrolled air movement wastes energy and increases the risk of long-term damage to building components." NorthGuy has provided an example of a small hole causing significant ice and moisture accumulation in a house that he lived in. In the GreenBuildingAdvisor.com article referenced above, the title is "Can Houses be 'Too Insulated' or 'Too Tight'?," and they answer that question with, "No. Green homes are insulated well, tightly built, and well ventilated."

Max Sherman, who probably has as many technical publications as anybody on the subject of air infiltration in residential buildings, asks the question, "Houses Need to Breathe...Right?" in this article. In that article, he goes on to title one section with "Leaky houses are not the answer." He explains how heat recovery ventilation systems (HRV) remove stale air, bring in an equal amount of fresh air, and recover most of the energy from the stale air and add it to the fresh air, conserving energy. The HRV that I have in my house does exactly that. It transfers about 70% of the sensible heat from the stale air as detailed here.

The use of air barriers and moisture barriers are two different phenomena. For example, Tyvek house wrap is an air barrier, and a liquid water barrier, but it lets water vapor penetrate the membrane. The issue with moisture is to limit moisture penetration into the structure, but then to allow some amount of drying to let moisture that does penetrate the structure to leave the structure. This is typically accomplished with Class III vapor retarders (greater than 1 perm, less than 10 perm) like latex paint used on the interior and exterior of the assembly, from buildingscience.com. This Building Science Corp. article has good information about the control of moisture in building assemblies. You are correct that Class I vapor retarders like plastic sheeting is now not recommended in the U.S., as it does not allow moisture that gets into the building assembly to easily dry out.

Another example of excellent thermal resistance without moisture condensation problems is the walls of my house. The walls are conventional 2x6 studs sealed to the OSB with foam and filled with wet-sprayed cellulose, followed by Sheet Rock covered with latex paint. Then outside the OSB is covered with 2" of XPS rigid foam. Moisture that does penetrate the latex paint does not reach the condensation temperature until the midway into the rigid foam, which is unaffected by condensation. So it remains as mostly as water vapor in the structure until it has a chance to dry, typically to the interior, or the small amount condensed in the foam can dry to the interior or exterior. The 2" XPS rigid foam has a permeability for water vapor of about 0.55 (from Building Science Corp.), so it is a class II vapor retarder that allows limited moisture movement.

It takes a little planning to get a tight, well-insulated, energy-efficient house with good moisture control and good indoor air quality, but it is certainly possible by paying attention to what is already explained in the home building literature.

Re: Last month's gas bill

Having just gone through some of these issue with some classes I have taken, and working with some retro fit insulation contractors, vapor barriers are a true double edge sword. The reality can change over the course of the annual year. For example, the old days rule was to provide a vapor barrier on the heated side. The problem there is that the heated side changes changes over the course of the year. The problem is that with modern sheeting, like ply or OSB, the sheeting can act as a good VB, so now you have a situation where inevitable moisture from either outside the structure or inside, can be trapped in the wall (or ceiling) assembly leading to rot issues.

There are a number of often conflicting assemblies now in the field. It seems that spray foam in new work, and dense packed cellulose are a couple of the better alternatives. Proper dense pack cellulose serves as a very effective air barrier, which in turn reduces the need for a vapor barrier. Like so many things, many solutions create their own problems.

Old, leaky structures seldom rotted, new modern tight ones, while being energy efficient have issues that need to be addressed.

Back on the subject,

Tony

Re: Last month's gas bill

Cariboocoot wrote: »

Air conditioning is the culprit in reverse-flow conditions. Without a temperature difference between inside and out you don't get the vapourized moisture condensing at some point. So if all you do in Summer is open the windows, there's no problem. If you keep the house closed up and crank up the A/C then the interior becomes the cold spot relative to the exterior, and you've just turned the wintertime problem around. In areas where heating & cooling are used they will sometimes put a vapour barrier on both sides of the wall to stop the transmission in either direction.
...snip...

Note from the Building Science Corp. writeup on "Understanding Vapor Barriers":

Avoidance of using vapor barriers where vapor retarders will provide satisfactory performance. Avoidance of using vapor retarders where vapor permeable materials will provide satisfactory performance. Thereby encouraging drying mechanisms over wetting prevention mechanisms.

Avoidance of the installation of vapor barriers on both sides of assemblies – i.e. “double vapor barriers” in order to facilitate assembly drying in at least one direction.

Avoidance of the installation of vapor barriers such as polyethylene vapor barriers, foil faced batt insulation and reflective radiant barrier foil insulation on the interior of air-conditioned assemblies – a practice that has been linked with moldy buildings (Lstiburek, 2002).

Avoidance of the installation of vinyl wall coverings on the inside of air-conditioned assemblies – a practice that has been linked with moldy buildings (Lstiburek, 1993).

Enclosures are ventilated meeting ASHRAE Standard 62.2 or 62.1.

So rather than a vapor barrier (perm < 0.1) like poly film on both sides of an assembly that would trap water in the assembly, the current recommendation is to use a vapor semi-permeable material (1.0 < perm < 10) on both sides of the assembly to limit propagation of water vapor into the assembly, but to still allow it to dry. That is the reason for recommending latex paint on both the interior and exterior of an assembly.

Re: Last month's gas bill

ChrisOlson wrote: »

That's what we did - put in a bigger furnace - 200,000 BTU for 2,100 sq ft. But the only caveat is that we heat with wood so the energy is basically free (wood harvested from our own land) and carbon neutral, with the power for the forced air blower provided by wind and solar.

The only real downside to the wood heat is that it is the only source of heat we have. We can leave and go someplace in the winter for 2-3 days with no problem and it just gets cold in the house. But longer than that time we have to have somebody babysit the house to keep the furnace going because it will get too cold in the house.

We also burn wood from our land. We have lots of pines infested with mistletoe. They often die and provide endless supply of wood. However, our main heat is from our gas furnace.

It's funny, but with the gas furnace we cannot leave for too long too. It's a new 98% efficient kind which produces few gallons of condensate every day, which is dripping into the septic tank. The supply is so slow that the syphon doesn't flush, but the water slowly drips through the system. This is not a problem if we live in the house and use water because the syphon does get flushed often. But, if left unattended, the slowly dripping water freezes at the end of the pipe, the septic tank eventually overflows and we get a sewer backup. I'll have to do something about this.

Re: Last month's gas bill

icarus wrote: »

A question might be, why are you taking the condensate drain to the septic, rather than just to daylight? I don't beleive that it is required to go to septic or sanitary sewer, just to daylight, (and be prevented from freezing.)

It simply goes to the floor drain, which eventually leads to the septic tank.

Taking it outside will definitely help. It may freeze by itself at -40C, but it may be easier to deal with than the septic. I'll need to think about that. Thank you Tony.

Re: Last month's gas bill

Typically a floor drain shouldn't go to the sewer/septic, especially if it doesn't hve a trap. Floor drains typically run to weeping tile drains and footing drains, out to daylight. It is possible to have one Plumbed to the sewer, but that would be rare. I have seen folks put thier condensate drains on a small pump to pump to daylight. If you wish to keep it simple, drain it into a five gallon bucket, with a Rule bilge pump to pump automatically. Proper pitch and higher volume would eliminate freezing.

Tony

Re: Last month's gas bill

icarus wrote: »

Typically a floor drain shouldn't go to the sewer/septic, especially if it doesn't hve a trap. Floor drains typically run to weeping tile drains and footing drains, out to daylight.

We don't have a storm drain. Everything goes to the septic tank. Of course, there's a trap on every drain. I think it's typical for rural houses.

Re: Last month's gas bill

NorthGuy wrote: »

We don't have a storm drain. Everything goes to the septic tank. I think it's typical for rural houses.

That has been my experience, for everything but a sump pump which would be too much water for the septic system and avoids freezing problems by being a pump-driven "drainback" system.
I suppose you could put in a reservoir and a pump to daylight for your gas furnace condensate. Or just a reservoir that tipped into the floor drain whenever it got above a certain level. The reservoir would be have to be large enough to trigger the siphon.

Re: Last month's gas bill

ChrisOlson wrote: »

...snip... but at all costs avoid using what has been proven over hundreds of years because it's too simple.

And then we would all need 250,000 Btu/hr furnaces like you are using. Can you imagine the impact on natural gas and oil supplies, carbon footprint to the atmosphere, and air pollution? Or if we all used wood, can you imagine the loss of forests?

The technologies required to build efficient, tight homes have been developed. Why not take advantage of them? The old technologies were the best available in their day, but the inhabitants did not try to heat their homes to 72 F (22 C) on those cold winter nights like people often want nowadays. If you want to live in a leaky house, fine, open the windows and enjoy the fresh air. Just don't waste the earth's resources trying to heat it to today's comfort standards.

A house is just like a human. If you were forced to wear one article of clothing all year round, 24 hours a day, what would it be? A rubber rain suit poly barrier under your clothes, or a waterproof breathable Tyvek jacket over your clothes?
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Chris

If you are implying that I was suggesting using polyethylene vapor barriers on the inside of houses, you need to reread the posts above, in particular the exchanges with Cariboocoot, and all the links that I provided to the reference materials on control of water vapor in house structures. There is no suggestion about using polyethylene vapor barriers by me, or in any of the reference material. What I did suggest is using class III vapor retarders, also known as semi-permeable materials, like latex paint on the interior, and latex paint and/or Tyvek on the exterior. These materials limit the transport of liquid water and water vapor into the assembly since the perm rating for most latex paints is less than 10, but still allow some drying of the assembly, which is roughly analogous to your "breathable Tyvek jacket."