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Blower door test & Combustion analysis done today...1st stage more efficient

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#61 ·
hearthman said:
Teddy makes a great point that all testing, no matter how comprehensive, is still just a snapshot in time. Stack effect is minimal in summer and pronounced in winter. Wind effect as Teddy noted. Operational conditions within the home..., etc.

To reiterate: passive MUA is very unreliable. ASHRAE did a study proving it. If you want Ventiation, your best bet may be a HRV or ERV. These guys can better discuss those options than me. Yes, you need to seal the thermal envelope and yes, you need to ventilate. Unless air is moving both in and out, you ain't ventilating.
BTW, the ASHRAE std. is 0.35 ACH as a min. ventilation rate and that is for people--not to ensure against backdrafting. Only powered MUA properly balanced can do that. Typically, these fans are wired with a slave switch, such as a current sensing switch to the two largest exhaust hogs in the home. Typically, this means the clothes dryer and kitchen hood. The new ASHRAE 62.2 now calls for powered MUA for ALL exhaust devices in new construction, though it is seldom done.
BTW, in order to qualify as a MUA grille, your door would need to be undercut a min. 3"!
HTH and glad to see someone who is educating themselves on this stuff.
Hearthman
Click to expand...
Sometimes stacks invert, I have measured it myself.

If you feel you need the constant source of fresh air the HRV and ERV are your best choices with respect to energy efficiency. An HRV balanced and running at 0.35 ACH or even half that rate will make your house so dry in the dead of winter your lips will split open unless you add a humidifier. You ventialte to stop winter time window condensation then you humidify because it is too dry. I sort of prefer to ventilate on a rise in RH myself to keep the windows clear. I figure your windows tell you in the winter if you are getting enough air or not.

I would not be overly worried about intermittent exhausts like clothes dryers etc, unless it had an impact on venting of combustion products. When there are no combustion problems, the intermittent exhaust of the magnitude of a clothes dryer are not a big problem.

What can be problematic in really tight homes, and we are talking less than 0.1 ACH in winter, are Italian Stainless Steel Kitchen Hoods and Jenn Airs trying to pull 300, 600 or even 1200 CFM out of a house. For one, these appliances will sure let you know if your plumbing traps are primed.

300 CFM, I have seen a passive interlocked motorized damper work fine to allow make up air in -- 600 and 1200 CFM you are into the realm of a make up air fan and most likely an electric duct heater to temper the air up above freezing so you do not freeze water pipes in a basement.

I think a system that can do 0.3 to 0.35 ACh intermittently when needed is fine myself, but I tend to make stuff up as I go along.

You need a system to ventilate.

You need a system for combustion air, i prefer direct vent

You can also need a make up air system for the big exhausts.

If you need all three you need three systems. One system does not serve all.
 
#62 ·
Carnak said:
You need a system to ventilate.

You need a system for combustion air, i prefer direct vent

You can also need a make up air system for the big exhausts.

If you need all three you need three systems. One system does not serve all.
Click to expand...
I think we all know this. But this thread is not about those parameters. Design conditions.
 
#63 ·
energy star said:
I think, or rather feel the test is flawed and will give no exact information. It is extracting data and using that data in an extrapolation type of procedure to get an answer. This answer is elusive and can not be one that is a constant. The results will never be the same.
Click to expand...
I whole heartedly agree and know where you are going. However, HVAC is my profession and we extrapolate a lot (cannot have best conditions each and every time trying to alleviate a problem.) Ode to the labratory where we can set the ideal! :D

To borrow from another, we seek to be accurate, not precise.
 
#64 ·
stack effect, hot air rises goes to the top floor , pressurizes ceiling and walls windows above the neutral plane. So air escapes high and the lower area goes negative. Then theoretically all the infiltrating air comes in around basement window frames etc, other places below the neutrral plane.

What other forces can also make a basement negative?

How about when you use joist lining or panning as some call it to make your return branch ducts. Probably half the return air the furnace draws in is in the basement and it is unintentional. Leaks right on the unit, and from those floor joists. Maybe the return system even pulls stuff down from an attic.

So this kind of depressurized basement or wall cavity leaks do not care if it is summer or winter. You get a pressure differential year round.

I would also say in the cooling climates, where they run all the ducts in the attic, that most of the infiltration is caused by duct leaks and this again does not care if it is summer or winter.

And when you have all your supplies and returns in the ceiling, cold air falls to the floor and pressurizes low. This is an inverted stack. Cold air falling down from the second floor to the ground floor will also suck air out of an attic and in backwards through exhaust fans
 
#65 ·
energy star said:
I think we all know this. But this thread is not about those parameters. Design conditions.
Click to expand...
So what is it exactly about now, dividing ACH 50 numbers by 20 to come up with my house will leak at 0.33 ACH?

Splain it to me Lucy
 
#66 ·
Carnak said:
So what is it exactly about now, dividing ACH 50 numbers by 20 to come up with my house will leak at 0.33 ACH?

Splain it to me Lucy
Click to expand...
I simply saying you are tossing more parameters into this equation. If we have a "Jenn-air" with a killer exhaust we know a make up air system will be necessary. We realize or rather I realize what you are saying, but what you have described is not in the OP original post. It appears that it is justification for more number crunching and abbreviation in an equation that does not merit it.
 
#67 ·
the original post was about combustion numbers at low fire and high fire. Perhaps you would like to moderate and nudge everyone on this thread back to this topic?
 
#69 ·
okay how about this. A blower door is good for finding where your leaks are, but is basically as useful as tits on a bull when trying to figure out the leak rate of a tight home?
 
#70 ·
Yo, dude chill out, The test was not done in a fashion that would produce an accurate result. It was done in a manner to appease the home owner in a VERY basic manner. He has a leak at his hot water heater flue. He has a leak at his basement door. and who knows where else. The furnace he has, I believe has a combustion air intake. So he has a water heater in his """""CAZ zone""""" the basement leakage and sq footage covers that. You really think this homeowner needs to heat or cool outside air for ventilating? That would negate the savings from all this high efficiency equipment and effect the payback time and the money spent on the initial investment in the first place.
 
#71 ·
Actually guys, and please do not flame me for this, this is a new thread from a post of whether the HO would add a Hepa filter to aid in allergen control. The bigger picture is that as a consensus, building science won out in fixing an IAQ problem. Because the HO is a very active, knowledgable, and very much part of this process, we are able to take things to a very different level. Makes us all smarter in the end, doesn't it?
 
#72 ·
I am not trying to be the thought police here so I do not really need to chill.

You either directly or indirectly heat/cool ventilation air.

Now if you are worried about a water heater, then perhaps you add a combustion air system for it, but then again you said you already knew this and I was being off topic by mentioning it.

Passive intakes not a guarantee, there are powered intakes for this purpose. A better choice would be to go with a power vented water heater since he already has a condensing furnace.

What colour should he paint his basement?
 
#73 ·
energy star said:
I simply saying you are tossing more parameters into this equation. If we have a "Jenn-air" with a killer exhaust we know a make up air system will be necessary. We realize or rather I realize what you are saying, but what you have described is not in the OP original post. It appears that it is justification for more number crunching and abbreviation in an equation that does not merit it.
Click to expand...
usually when you quote someone, it implies you are talking to the person you quoted, or you wish to discuss something the person you quoted just wrote.

Sort of like you did when you quoted me here. I do not really get why something I was saying to hearthman has your panities in a knot.

So I am sorry if what I say is not what you want to discuss, but you are free to ignore me. Or you can buy the site and maybe control me herr furhur.
 
#74 ·
Funny with the basement color. I mean really thats very funny, I'm laughing also. But you of all people "negative pressure sucks" would understand. You can pull a vacuum on an entire basement (John Tooley). But I won't get into to that. A power vented water heater would be a better choice.
 
Discussion starter · #76 ·
OK gentlemen (and ladies).
I am all for helping to increase the knowledge base of the industry if I could.
Let's say we take this to the next level.

For those on the sidelines that are still a little unclear, I am attaching what I believe is a key (no pun intended) document to the entire discusion. It is how I learned to calculate my own numbers and in conjuction with the posts in this thread, have given me the insight I needed to make some informed decisions. It is 17 pages but well worth the reading to help further your understanding.
Good Reading.

Key
 
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#77 ·
key1cc said:
Not being a patient man...I could not wait for my report so I ran the numbers myself :).

As stated earlier the calculated minimum CFM50 number is 2864 as done by the pro. I remeasured everything myself and re-ran the calculations and got a calculated minimum CFM50 of 2772 (which I figure is close enough since I spent some time to be as accurate as possible and I took into consideration the different ceiling height in the family room.) When I convert my minimum CFM50 number to ACH50 (air changes per hour at -50 pascals) I get 5.4. This is the minimum recomended ACH50 for my home. When I plug in the actual blower door CFM50 number of 3400 my actual ACH50 number becomes 6.6 which converts to 0.33 ACHnat. I interpret this as meaning my home naturally exchanges the total volume of air once every 3 hours. I do not know if that is good or bad for air quality or for efficiency in NJ. Any insight here would be much appreciated.
Thanks
Key1
Click to expand...
I think you may have miscalculated somehow. If you use the LBL method [which is considered more accurate] to calculate ACHn [natural air exchanges per hour] the formula is ACHn=CFM50 * 60 / (n*V)
So the n-factor for 2 story above grade normally shielded in NJ is 14.8
Volume would be 4100sqf x 8’ = 32800, I used 8’ but know you said something about a vaulted ceiling. I also included the basement since the basement walls are almost always the pressure boundary.
I come up with your existing ACHn at .42, if your goal is .35 which is a good recommended goal your CFM50 would be 2832, pretty close to the number you have been given.
 
Discussion starter · #78 ·
stvc said:
I think you may have miscalculated somehow. If you use the LBL method [which is considered more accurate] to calculate ACHn [natural air exchanges per hour] the formula is ACHn=CFM50 * 60 / (n*V)
So the n-factor for 2 story above grade normally shielded in NJ is 14.8
Volume would be 4100sqf x 8’ = 32800, I used 8’ but know you said something about a vaulted ceiling. I also included the basement since the basement walls are almost always the pressure boundary.
I come up with your existing ACHn at .42, if your goal is .35 which is a good recommended goal your CFM50 would be 2832, pretty close to the number you have been given.
Click to expand...
It is possible that you may be correct but as my teacher alway said....show your math. Here is mine. The actual more precisely measured sq feet including basement is 3745sqf. Considering the one vaulted ceiling the total cubic feet is 30918 CF (The 4100sqf you used was the analysts estimate which was based on measuring the basement and making assumptions for the upper floors. I actually measured the upper floors to get the exact values although both are so close they come out to the same value in the end). Also according to page 5 of the the BPI document that I attached in my previous post the N-factor for NJ is the same as that for NY which is 15.4 not 14.8. The measured blower door CFM50 was 3400 with basement included. Plug those numbers in and you get a ACH50 of 3400x60/30918 = 6.6. Divide that by 20 for your ACHnat and you get an existing ACHnat of 0.33.
According to page 4 of the document I attached in the previous post, I interpreted that the N-factor is only considered when calculating the BAS minimum CFM50 not the actual measured value of your home. It is a standard not a measurement. (That part I am not 100% clear on).

Lets look at the LBL calculation you referenced.
The difference is that I would take my numbers and include the N-factor:
3400x60/30918x15.4 = 0.42

Which is the ACHnat you referenced.

That value has different implications because it suggest that I do not require mechanical ventilation whereas the 0.33 implied that I did.

Hmmmm, any BPI analyst out there know for sure if the n-factor is considered on the actual measurement? Or just on the standard.

I think STVC is actually correct as it makes more sense to me and a few of us may have just reached a new level of enlightenment :)

I love quoting the one pro here who's tag line is

"we never stop learning until we are dead"

Key1
 
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#79 ·
BPI model

I have not taken the BPI course nor read fullly through its protocols but based upon the document presented, I do have a few observations:
ASHRAE 62.2-89> There is now a 2007 Revision of this document, which has been revised every three years. Not sure why they are basing this on a very old revision of this std.
UL 2034 CO alarms> Has been well discussed the flaws with these alarms. Do not offer adequate protection on the low end, as stated on their packaging and are very unreliable. The BPI protocol calls to halt the test if >35ppm CO but you would die first if you were relying on one of these alarms to protect you. Should use unlisted low level CO monitors: CO Experts or NSI 3K
Worst Case Conditions> very disjointed but appears to turn of all appliances at one time then point test. A worst case test is just that. You won't know when you're reached it until you turn on all exhausts and mechanical ventilation individually then collectively. Ususually, when I encounter houses with multiple forced air systems, one actually improves the CAZ pressure profile while others hinder. For instance, in a house with 3 systems, you are running them individually then collectively. This means you draw up a matrix to cover the combinations
Spillage guidelines> It says to test for spillage but does not reference how this is determined. For instance, it discusses using chemical smoke or mirror to test for spillage at a draft hood??? Now that's quantitative and reliable (not). At what point? It talks about spillage after one minute but the ANSI Stds. allow spillage for up to 10 minutes. Few water heaters cycle that long. That means it can legally backdraft for an entire firing cycle.
This test requires closing the fireplace damper> A burning open hearth can exhaust 400-600cfm up the chimney and is probably the most sensitive combustion appliance for spillage, yet it is not being tested? How do you know the WH won't backdraft when the Fp is burning under Worst Case? Will the Fp spill smoke under Worst Case?

Still, I feel they are on the right track. Over time, we learn more. That's why we have code and std. revisions. It ain't perfect but we do need to be alert to defects in our logic and fight to ensure we are not making false assumptions in our test methodologies.
Hearthman
 
#80 · (Edited)
key1cc said:
It is possible that you may be correct but as my teacher alway said....show your math. Here is mine. The actual more precisely measured sq feet including basement is 3745sqf. Considering the one vaulted ceiling the total cubic feet is 30918 CF (The 4100sqf you used was the analysts estimate which was based on measuring the basement and making assumptions for the upper floors. I actually measured the upper floors to get the exact values although both are so close they come out to the same value in the end). Also according to page 5 of the the BPI document that I attached in my previous post the N-factor for NJ is the same as that for NY which is 15.4 not 14.8. The measured blower door CFM50 was 3400 with basement included. Plug those numbers in and you get a ACH50 of 3400x60/30918 = 6.6. Divide that by 20 for your ACHnat and you get an existing ACHnat of 0.33.
According to page 4 of the document I attached in the previous post, I interpreted that the N-factor is only considered when calculating the BAS minimum CFM50 not the actual measured value of your home. It is a standard not a measurement. (That part I am not 100% clear on).

Lets look at the LBL calculation you referenced.
The difference is that I would take my numbers and include the N-factor:
3400x60/30918x15.4 = 0.42

Which is the ACHnat you referenced.

That value has different implications because it suggest that I do not require mechanical ventilation whereas the 0.33 implied that I did.

Hmmmm, any BPI analyst out there know for sure if the n-factor is considered on the actual measurement? Or just on the standard.

I think STVC is actually correct as it makes more sense to me and a few of us may have just reached a new level of enlightenment :)

I love quoting the one pro here who's tag line is

"we never stop learning until we are dead"

Key1
Click to expand...
the calculation procedure based on a blower door test has evolved somewhat from dividing the ACH50 by a fudge factor of 17 to 20.

The net result from the blower door test, besides locating where your leaks are is to give you a conservative infiltration value that if you use it to size your heating equipment, you will not be undersizing your heating equipment.

Now I brag about my own home but with normal winds maybe I leak 5 CFM. Scale that up by a factor of 20 and that is 100 CFM, which is probably 55% what my clothes dryer exhausts. So what I have noticed is my ears do not pop like I have instantly been depressurized by 50 Pa when my wife dries a load of clothes.
 
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