I have a 93 year old house that I've owned for two years. It's small under 800 sq feet and one level (bungalow). A year ago I had an energy audit done with the camera and the blower door and I was leaking almost 6 times the min ventilation amount. After having my attic floor sealed off, the rim joists spray-foamed, and some caulking around my windows and doors, I have a pretty tight house! I had the test out procedure done yesterday and it said I was leaking about 945 cubic feet at 50 pascals. I'm at around 1.1 ach which my auditor told me it's in the top 3 best improvement he's had.

Tomorrow I'm taking my insulation in the attic all the way up to R-60 with blown-in fiberglass. My heating bills were cut in half by about 50%. Some of that can be attributed to the mild winter we had, but the improvements I made are a big part as well and I can feel the difference in how much more comfortable the house is. I'm hoping that my air conditioning bills will drop quite a bit after the attic is insulated tomorrow.

I have a question for those who care to chime in.

When do I want to think about mechanical ventilation? I've read a little bit about it, but I'm not sure if my house is so tight that it needs it. The reason I have been thinking about this is because lately I've been thinking a lot about indoor air quality. I'd like to install some type of whole house air filtration system, but I have heard that there are ERV's or HRV's that also filter the air killing two birds with one stone.

Anyone have any thoughts?

At 1.1ACH/50 you definitely need a ventilation strategy. Given your high summertime latent cooling loads an ERV is preferable to HRV.

The house is small enough and has a reasonably open floor plan, you may be able to do it with a pair of the little Panasonics (see: http://shop.panasonic.com/shop/model/FV-04VE1 ) rather than a bigger deal ducted ERV system. Putting one in the bathroom and one in the kitchen could be reasonable approach since those are usually the biggest indoor humidity and air-pollution sources in non-smoking households.

Congratulations- 1.1ACH/50 is a truly difficult level to achieve in a retrofit- it takes careful planning & implementation even on new construction!

With a house that tight you may want to monitor the indoor relative humidity in winter. If it's consistently above 35% RH @ 70F (dew point ~40F) in mid-winter, adjust the ventilation rates higher (or run a dehumidifier). High wintertime humidity can load up the sheathing on the exterior with moisture. On plank-sheathed 1920s bunglows the risk of rot related to that is a lot less than with modern OSB-sheathed construction, but keeping the interior in the 30-35% RH range is good insurance- healthy for the humans, healthy for the building materials. The type & condition of the siding affects that as well.

In summer you want to back off the ventilation rates a bit to avoid taking on moisture from the outdoor air, once average outdoor dew points are north of ~55F or so.

Low density R60 fiberglass won't help the air conditioning as much as R60 cellulose would, but if you were starting out at R19 batts or something it'll still do a LOT. Fiberglass is somewhat translucent to infra-red, under a hot roof deck the insulation 2" below the top of the insulation ends up being several degrees hotter than the attic air temp, so you're in effect insulating against a higher temp with ~R6-7 less insulation. With cellulose the top of the insulation is the hottest part of the insulation layer, and only modestly higher temp than the attic air when the roof deck temps are peaking.

It's not worth quibbling about at this point, but if the fiberglass settles very much over the next several years (as sometimes happens), over-topping it with 3-6" of cellulose to bring it back up to R60 would improve both the winter & summer performance by more than the increased ASTM C 518 rated R value would imply.

The plan for ventilation should have been made before the air sealing was done. Get this done before beefing up your insulation. If you go with an exhaust only approach you will be in the attic distrubing insulation.

I suggest you use cellulose. It is less air pourous which makes it perform better.

Also do you have power vented appliances. In a tight house you have to worry about appliances back drafting.

Posted By strategery on 05 Apr 2012 06:33 PM
I have a 93 year old house that I've owned for two years. It's small under 800 sq feet and one level (bungalow). ...snip...  I had the test out procedure done yesterday and it said I was leaking about 945 cubic feet at 50 pascals. I'm at around 1.1 ach which my auditor told me it's in the top 3 best improvement he's had.

This would be a very good number for tightness, especially for a 93-year old house.  I am having trouble coming up with the number that your auditor got, unless I am guessing your house dimentions incorrectly, or am doing the calculations incorrectly.  If your ceiling height is 8', and the floor area is 800 ft^2, then the house volume is 8 ft x 800 ft^2 = 6,400 ft^3.  If you have a conditioned full basement that is 8' below the first floor, then that volume is doubled, but you did not mention a conditioned basement.  You have a leakage rate of "945 cubic feet," which I will assume is cubic feet per minute.  So the leakage rate at 50 Pa would be 945 ft^3/min x 60 min/hr = 56,700 ft^3/hour.  If I divide that leakage rate by the 6,400 cubic feet assumed house volume, I get 8.9 air changes per hour (ACH_50), not an unreasonable number for an old house that has been made reasonably tight.  This would correspond to a normalized natural ventilation rate of roughly 0.45 NACH, which probably would not require mechanical ventilation.  If there is a conditioned basement that doubles the house volume, then the leakage rate is 4.4 ACH_50Pa. 

Perhaps I have guessed the house volume wrong or have messed up the calculation?  

I really don't know very much about this I'm just now starting to learn about it. I saw the blower door results and it said 50 pascals and 945cf per minute. My basement is not conditioned. My house is 768 square feet to be exact. Maybe Dana can chime in?

strategery-

What is your ceiling height?

It's 8 feet.

So,
Volume = area x height = 768 ft^2 x 8 ft = 6144 ft^3.
Leakage rate = 945 ft^3/min (cfm)
Leakage rate = 945 ft^3/min x 60 min/hr = 56,700 ft^3/hr
Normalized leakage rate = leakage rate per hour / volume = 56,700 ft^3/hr / 6144 ft^3 = 9.23 air changes per hour (ACH) @ 50 Pa differential pressure

Data from Fig. 5 of "Air Tightness of U.S. Dwellings," by Max Sherman and Darryl Dickerhoff, LBL-35700 (http://epb.lbl.gov/publications/lbl-35700.pdf):
Natural leakage rate for 100 year old house = 1.12 NACH (@ ~4 Pa)
Approximate conversion factor from natural leakage to leakage at 50 Pa = 20 x NACH, so, 
20 x 1.12 NACH = 22.4 ACH @ 50 Pa

So the average 100-year old house has a leakage at 50 Pa of 22.4 ACH, while your retrofitted house at 9.2 ACH_50 is only 41% of that leakage rate, or 59% lower than average, a good value.   

I don't understand how your energy rater got 1.1 ACH_50 Pa out of that.  You might forward this information to him and ask that question. 

You do not need mechanical ventilation as your natural ventilation is sufficient.

I really don't know, but I'll call him and ask. Maybe I got something wrong? I was looking at the blower door's cpu myself and it said 945. Does that usually mean per cubic foot? He used two different numbers that I know about when calculating my house' square footage. He took both with and without the basement.

Strategery -

Agree with Lee's numbers.

Please feel free to post the printout if you received one.

Lee - this document by the same author as the one you reference

(http://www.buildingscience.com/documents/guides-and-manuals/gm-review-residential-ventilation-technologies)

says that the minimum ventilation is "3 cfm per 100 sq. ft plus 7.5 cfm per additional occupant"

Why is the recommendation based so heavily on number of occupants?

For 4 people in a 1000 sq foot home the required ventilation would be (3 cfm X 10) + (7.5 x 4) = 30 + 30 = 60 cfm

In this case the formula requires as much ventilation for the people as for the house.

As long as they are non-smokers and the humidity is fine then why care about # occupants?

If strategery has 945 cfm at 50 Pa then (assuming this is roughly linear) he would have 945/17.5 = 54 cfm at 4 Pa.

The 17.5 comes from page 6 of your reference describing the ratio between ACH50 and natural leakage rates.

So if strategery has 4 occupants at home then it seems to me ASHRAE 2004 says he needs (3 cfm x 9.4) + (7.5 cfm per occupant x 4) = 28 + 30 = 58 CFM of ventilation.

So with 4 occupants he might be slightly under ideal ventilation (if you accept that ventilation should depend on occupants which I questioned above).

Todd-

I do not serve on the ASHRAE ventilation committee, but the reasons that I can think of for a ventilation standard include:
1.  Remove humidity created from showers, cooking, etc.
2.  Remove contaminants from household items like volatile organic fraction (VOF) from floor finishes, plastics, paints, adhesives, etc.
3.  Remove contaminant from human activities like CO2 from breathing, fireplace smoke, fingernail polish, adhesives, passing gas, bathroom odors, etc.
4.  Remove contaminants from cooking including both combustion products from natural gas and food odors.
5.  Remove radon in those areas where radon is a problem.

Some of these are house size dependent, and some are dependent on the number of inhabitants.  For example, more people would imply more showers, more cooking, more bathroom visits, etc.  Therefore a standard based on both house size and number of people sounds reasonable. 

I think that you have misinterpreted ASHRAE 62.2-2004, which is quoted in the link that you provided as "3 cfm per 100 sq. ft plus 7.5 cfm per additional occupant which includes a 2 cfm per 100 sq. ft allowance for infiltration"  What does this mean?  I think that it means that they were assuming that houses leaked with a natural infiltration rate of at least 2 cfm per 100 sq. ft. of floor space, and that additional mechanical ventilation needed to be added to achieve the remaining 1 cfm per 100 sq. ft. plus 7.5 cfm per occupant.  The 7.5 cfm may have meant per occupant beyond the first occupant.  One reason that I interpret it this way is knowing how engineering committees work, with small changes to the process. 

Compare three different ASHRAE 62.2 standard:
1.  "Traditional" 62.2 or 0.35 air changes per hour (ACH).
2.   ASHRAE 62.2-2004, with the interpretation that it means add mechanical ventilation to achieve 1 cfm per 100 sq. ft. plus 7.5 cfm per occupant.
3.  ASHRAE 62.2-2007, ([number of bedrooms + 1] times 7.5 cfm plus [0.01 cfm/ft2 of conditioned space]) cfm.  (I assume this replaced the 2004 standard since nobody knew what the 2004 standard meant.)  

Apply these three standards to four houses:
House dimensions
Floor area     sq ft   1000    1500    2000    3000
Wall height    ft             8          8          8          8
Volume         cu ft   8000   12000 16000  24000
No. of bedrooms          3          3          4          5
No. of inhabitants         3          3          4          4

Stand.#1      cfm        47        70        93      140  
                   ACH      0.35    0.35      0.35    0.35  
Stand.#2     cfm       32.5     37.5      50        60
                   ACH      0.24     0.19     0.19    0.15 
Stand.#3     cfm        40        45       57.5     75
                   ACH      0.30     0.23     0.22    0.19

If you use the other interpretation for standard #2, ASHRAE 62.2-2004, then those ventilation rates are way out of line with the rates for the other standards.  At any rate, the ASHRAE 62.2-2004 has been replaced by ASHRAE 62.2-2007, so let us not worry about what they meant to say.  The normalized natural air changes per hour for Stratergy were higher than the values shown above, so he should not need mechanical ventilation unless he misread or misinterpreted the flow rate measurement during the blower door test.

Posted By strategery on 14 Apr 2012 09:21 PM
I really don't know, but I'll call him and ask. Maybe I got something wrong? I was looking at the blower door's cpu myself and it said 945. Does that usually mean per cubic foot? He used two different numbers that I know about when calculating my house' square footage. He took both with and without the basement.

You should ask the person who performed the test. 

This is a little bit more technical than I'm able to understand. I need to get better educated before I can comment on any of this.

All that I know is that I spent some money foaming my attic and my rim joists, replacing 4 basement windows, and I personally spent many hours re-caulking every window and door. I FEEL a dramatic difference. My natural gas usage is down by 2/3 (again, some of that due to milder winter as compared to last year).

I notice in the kitchen I get condensation on the inside of the windows. Is that because of vapors trying to escape? When I open those windows to ventilate the kitchen the condensation goes away.

strategery-

Sorry that it got so technical, but we were just trying to sort through the confusing spec given in the ASHRAE ventilation spec that they came up with in 2004. That spec was replaced in 2007 anyway, so it does not matter.

Your house appears to be tight for a 100-year old house, being less than 1/2 of the leakage that the average house of that age has. It might even be much tighter than that, but we are unable to get agreement between the air flow rate that you reported and the air changes per hour that your rater came up with. Only the rater can answer that question. If you have a written report from the rater and could scan it and post it, then we could take a look at that.

You have dramatically reduced your natural gas usage, and made the house more comfortable, and that is really the bottom line. Your efforts have paid off handsomely!

Condensation occurs when the inside temperature of the glass surface is below the dew point temperature of the air. As the house gets tighter, it will increase the likelihood of condensation on the windows. Using a kitchen exhaust fan when cooking might help reduce the condensation.

It would be a good idea to get a hygrometer (to detect humidity levels) or two in the house to measure relative humidity. I know the folks here would say the only real effective way would be a wet bulb, but a couple of 2 to 3 dollar thermometers with a humidity gauge from Lowe's or Home Depot (Accurite makes them) will at least give you a general idea of how humid the inside of the house is. The condensation on the windows is a good indicator that the relative humidity in the house is too high, and you need to ventilate and/or dehumidify.

-Rosalinda

I actually have one by accurite in my basement that measures humidity down there. I keep my basement humidity around 50% this time of year by running my dehumidifier. My indoor humidity is usually around 50-55% upstairs. I am surprised if that is too much. Could it also be that the windows are old and maybe the seal has failed?

Lee

Thanks for a detailed and very helpful clarification.

Removing radon and VOC's seems important and these are related to building size.

I'm having trouble seeing the importance of removing CO2.

I'm aware the CO2 poisoning may occur from rebreathing air in a very confined space (mine shaft - ship hold) but I'm not aware of this from a house or building.

Todd-

Don't you remember Apollo 13? The buildiup of CO2 was one of many concerns during that mission after the service module had an explosion. The use of lithium hydroxide cannisters from the lunar module in the command module air circulation system allowed the guys to control CO2 levels enough to make it back alive. (I think the ones in the lunar module were square, and the holder in the command module was round, so it took some duct tape to bring those guys home! That was a true story...I was working at NASA at the time.)  Of course, that capsule was a lot smaller and tighter than a house.

Some people monitor CO2 levels and use that as one of the control parameters for turning on ventilation systems.  Others use humidity.  Most fresh air ventilation systems do not include any sensors.   

From: http://www.dhs.wisconsin.gov/eh/che...ioxide.pdf

WILL EXPOSURE TO CARBON DIOXIDE RESULT IN HARMFUL HEALTH EFFECTS?

Exposure to CO2 can produce a variety of health effects. These may include headaches, dizziness, restlessness, a tingling or pins or needles feeling, difficulty breathing, sweating, tiredness, increased heart rate, elevated blood pressure, coma, asphyxia to convulsions and even frostbite if exposed to dry ice. The levels of CO2 in the air and potential health problems are:
• 250 - 350 ppm – background (normal) outdoor air level
• 350- 1,000 ppm - typical level found in occupied spaces with good air exchange.
• 1,000 – 2,000 ppm - level associated with complaints of drowsiness and poor air.
• 2,000 – 5,000 ppm – level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present.
• >5,000 ppm – Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma and even death.

Posted By strategery on 16 Apr 2012 10:05 PM
I actually have one by accurite in my basement that measures humidity down there. I keep my basement humidity around 50% this time of year by running my dehumidifier. My indoor humidity is usually around 50-55% upstairs. I am surprised if that is too much. Could it also be that the windows are old and maybe the seal has failed?

An indoor relative humidity of ~50-55% @ 70-75F is perfectly fine for a summertime or shoulder-season value, but if it's that humid in January there is serious potential for condensation/rot conditions in the walls or ceilings.  Any ex-filtration path would be at a more acute risk, but even vapor-diffusion through wall paint could load up the structural sheathing to mold-risk levels.  That wintertime risk factor plummets if you keep it at 30-35% instead.

Lee: If your house is as small and as tight as Apollo 13 you have a real CO2 risk.  In most houses it would take days-WEEKS even to run into SERIOUS CO2 issues, even it were hermetically sealed, assuming the door was open for at least 30 seconds per day.  CO2 is never an indoor air quality risk the way CO or VOCs can be.

[edited for spelling & grammar]