how to calculate infiltration

[bigjohnsons34]

hi, i just purchased the load calc program and I'm trying to figure out how to estimate the number of air changes per hour, it comes pre-set at .5, and when i was done with the house the numbers did not jive. i was just wondering if there was a formula or a setting that you guys used. thanks

[Phasewolf]

Best of my know there is no way to guess on that number. You need to have a blower door test done.

[larobj63]

Right, a blower door test is the scientific way to do it (and still not 100% accurate).

Infiltration rates are almost always determined by an educated guess, based on the building construction and all aspects of the envelope - the windows, doors, insulation type (spray foam really slows down ACH rates drastically).

0.5 is a "normal" or "average" house. Higher might be older construction, lower might be brand new with careful sealing of window joints and all plumbing and electrical penetrations.

But, the age alone does not dictate the ACH rate. An old house could have been more carefully crafted than a new one. Or, one specific area, like an attic hatch or a single pane, steel frame basement window, etc, can really tank an otherwise tight house.

AN IR camera can help identify leaks, but doesn't directly measure infiltration rates in any way.

Sadly, ACH can be a major component in a load analysis. And you must make a leap of faith educated guess at it. Consider big commercial buildings where you can't even think of doing a blower door test...

[WhoIsThat?]

http://en.wikipedia.org/wiki/Blower_door

You need to know the fan curve
http://www.greenheck.com/media/articles/Product_guide/perf_basics.pdf
of the fan that you are using, and you need to measure ~0.2" of water.

Build it [use a 1 hp motor] or lease it
http://www.trutechtools.com/Q46-Automated-Blower-Door-40wHard-Case41_p_862.html

[bigjohnsons34]

that machine looks nice, but how many people are really using one. and lets say all that you have is a set of blue prints to go off of, ( new house, addition, etc ) the load that i did, it called for 4.5 tons for a 4400 sq ft house with the infiltration set at .5, which would never keep up,

[Kevin O'Neill]

We use a blower door on a regular basis. We also use a flow hood on a regular basis. How can you do air conditioning properly if you don't measure air?

My blower door measures exhaust air flow using pressure drop across an orifice, not using the fan curve. A computer program calculates infiltration from that. Yours may be different.

[Phasewolf]

Also just because a house is new does not mean it was build correctly. My mother in law home is brand new and I would not even want that house if it was giving to me. 2 door walls both of witch will not close all the way or latch for that matter she has to put 2x4 to keep people out. All the windows feel drafty and the doors don't seem to be sealed too well. Outside wall plugs leak air like crazy how it passed inspection know one knows. From seeing the inspector and home builder talk they were best friends and they could be part of it.

[Carnak]

Blower door tested R2000 homes were about 0.07 ACH, typical Canadian Home built to current codes you would be conservative at 0.35 ACH, house that needs a humidifier probably 0.7 ACH or more

LBL had some ACH charts back in the day, sort of looked at construction quality (tightness), exposure to wind ( wind effect), and number of stories (stack effect) to come up with a conservative ACH value to assume. Something no more than two stories, in a suburban exposure with unselaed vapour barrier probably be 0.5 ACH

I think blower doors are great for finding the leaks, what ever air change number it gives you will be a conservative best guess, I believe once a house is truly tight the blower door numbers break down.

[mbarson]

A blower door is not the holy grail of infiltration but it does standardize a procedure that quantifies an ACH number compared to the size of the building being measured when square foot, cu ft of volume, and surface area is entered.

The interesting thing about infiltration and load calcs is how much an effect it has on the load outcome. This shows how important it is to take infiltration into account when doing load calcs (and the importance of air sealing). I think this is why equipment is over sized so often... Infiltration is an unknown variable.

If you don't test then it is just a (bad) guess, especially in retrofit. With all of the talk of the importance of doing a load calc on this web site I wish more emphasis was put on infiltration, testing for it, and using actual numbers for the load calcs. I do realize this takes a dollar investment, an understanding of the procedure, and an added cost to doing business that most contractors won't bother with. And yes, blower doors are great for building diagnostics, especially when used with IR.

[energy_rater_La]

ducts leak also. if you 'guess' at infiltration rate of house, you will also have
to 'guess' at duct leakage. return air chases contribute to duct leakage as does
return framing for ceiling mounted R/A

lack of themal barriers also contrubute to load of house.
common thermal barrier inadequacies are fireplaces open to
attic, dropped ceilings, over shower units, boxing above cabinets
in baths and kitchens, just to name a few.

best of luck.

[Carnak]

A blower door is not the holy grail of infiltration but it does standardize a procedure that quantifies an ACH number compared to the size of the building being measured when square foot, cu ft of volume, and surface area is entered.

The interesting thing about infiltration and load calcs is how much an effect it has on the load outcome. This shows how important it is to take infiltration into account when doing load calcs (and the importance of air sealing). I think this is why equipment is over sized so often... Infiltration is an unknown variable.

If you don't test then it is just a (bad) guess, especially in retrofit. With all of the talk of the importance of doing a load calc on this web site I wish more emphasis was put on infiltration, testing for it, and using actual numbers for the load calcs. I do realize this takes a dollar investment, an understanding of the procedure, and an added cost to doing business that most contractors won't bother with. And yes, blower doors are great for building diagnostics, especially when used with IR.

A lot has to do with the regional codes, the enforcement level/inspections and the typical workmanship.

Now I have done countless homes back in the day, equipment sized for for ambients like-24 to -30F.

Sometimes they need just a little more than what a 60K furnace could do so they got a 75. Other times right on the money.


In my opinion, there are some conservative values in load calcualtions, in addition to assumed air change rates, there is also below grade losses that are conservative. Other factors such as internal gains etc are ignored but they do play a part.

Then we hit two weeks of extreme weather and it was down below -40 every night. Surprisingly enough, I was not getting phone calls that people were freezing, and I really expected it .

Typical furnace size, gas, 60 to 75K, 80% to 90% AFUE.

Homes built to earlier code revisions were predictable as well when upgrading. Now yes you are guessing on an infiltration, but you also know what the existing heating system is so its not like you are going to come up with a size that freezes them.

Now if the region has poor construction quality, or poor code enforcement, it is going to be another matter.

If the homes were really dry in the winter and they were running humidifiers that was a sure sign to me that they leaked like swiss cheese.

Would not have ducts in an uncondioned space in a cold climate like where I came from too often.

In a humid location, and you suspect the chronic high relative humidity they experience in summer is because the unit is over sized, most likely they have a big problem with outdoor air moving through the building at a high uncontrolled rate and it could be very possible that leaking attic ducts, or a bad central return situation is causing this, with a greater impact than a bad envelope

for about $700 you can get a telaire CO2 meter, a data logger and some software. Can pretty much give you the infiltration info you are looking for, can tell you when there is a big problem of too much outside air moving through the building. It does not find the leak source like a blower door does, but can give you a much more realistic idea of how much air moves through the building

[Kevin O'Neill]

An air advice will tell much the same thing, although at a much higher cost. A blower door with pressure pans will show you if the problem is duct leakage, which can then be fixed.

Often, determining the leakage is not enough. You must fix the problems as well. Or show the homeowner what needs fixed.

[Carnak]

This thread is about infiltration rates and it is pretty hard to run a blower door test on a set of prints before the place is built.

Then it shifted to what is the infiltration rate of an exisiting building and the blower door came up. If you show up at the right time it takes one minute for the telaire to warm up and you know what the rate is, otherwise leave it in place for a few days with the data logger and you know the rate.

I think the blower door is valuable for finding the leaks, the root cause of most HVAC problems is a poor envelope.

I know what my own home leaks, and according to the math that is programmed into that blower door software, my ears should pop like I am going up in altitude when my wife dries a load of laundry, bit it does not happen.

[paul42]

that machine looks nice, but how many people are really using one. and lets say all that you have is a set of blue prints to go off of, ( new house, addition, etc ) the load that i did, it called for 4.5 tons for a 4400 sq ft house with the infiltration set at .5, which would never keep up,

I found HVAC Calc to be quite accurate. I am heating & cooling 4,000 sq. ft. with a 2 ton heat pump - and it has no trouble keeping up.

Put the duct work in conditioned space, shade the windows in the summer, make the house air tight and put in a fresh air duct to the return on the air handler.

[yourairman]

that machine looks nice, but how many people are really using one. and lets say all that you have is a set of blue prints to go off of, ( new house, addition, etc ) the load that i did, it called for 4.5 tons for a 4400 sq ft house with the infiltration set at .5, which would never keep up,


A company I worked for in the past dealt with the issue you are talking about. How to know what it will be before the house is built. To address this situation you simply put it into the contract. The contract for the heating and cooling system stated what tolerance there would be for duct leakage. If the ductwork did not meet the criteria than the contractor was responsible for fixing it. You could do the same thing for a new home. Require in the contract the home be build to a specific standard. Test it after the home is built and make the general contractor be responsible if it does not meet the standard. Also the cost for the testing should be in the price of the contract and be performed by an independenct contractor who specializes in blower door tests and building efficiencies.

[yourairman]

ducts leak also. if you 'guess' at infiltration rate of house, you will also have
to 'guess' at duct leakage. return air chases contribute to duct leakage as does
return framing for ceiling mounted R/A

lack of themal barriers also contrubute to load of house.
common thermal barrier inadequacies are fireplaces open to
attic, dropped ceilings, over shower units, boxing above cabinets
in baths and kitchens, just to name a few.

best of luck.


This is absolutely true as well as proper duct design. Just because you put in a 5 ton unit does not mean that is what you are delivering to the conditioned space.

[energy_rater_La]

nation wide average of duct leakage is 30%
although they don't specify how much is duct leakage
and how much is return leakage, I think based on my testing,
that this is a good average. some leak more, but
most don't have less leakage.
over the years I've learned how to achieve 5%, but it is a LOT of
sealing! in my area about the best is 10% for companies specializing
in this level of sealing.
best of luck.

[udarrell]

A lot has to do with the regional codes, the enforcement level/inspections and the typical workmanship.

Now I have done countless homes back in the day, equipment sized for for ambients like-24 to -30F.

Sometimes they need just a little more than what a 60K furnace could do so they got a 75. Other times right on the money.


In my opinion, there are some conservative values in load calcualtions, in addition to assumed air change rates, there is also below grade losses that are conservative. Other factors such as internal gains etc are ignored but they do play a part.

Then we hit two weeks of extreme weather and it was down below -40 every night. Surprisingly enough, I was not getting phone calls that people were freezing, and I really expected it .

Typical furnace size, gas, 60 to 75K, 80% to 90% AFUE.

Homes built to earlier code revisions were predictable as well when upgrading. Now yes you are guessing on an infiltration, but you also know what the existing heating system is so its not like you are going to come up with a size that freezes them.

Now if the region has poor construction quality, or poor code enforcement, it is going to be another matter.

If the homes were really dry in the winter and they were running humidifiers that was a sure sign to me that they leaked like swiss cheese.

Would not have ducts in an uncondioned space in a cold climate like where I came from too often.

In a humid location, and you suspect the chronic high relative humidity they experience in summer is because the unit is over sized, most likely they have a big problem with outdoor air moving through the building at a high uncontrolled rate and it could be very possible that leaking attic ducts, or a bad central return situation is causing this, with a greater impact than a bad envelope

For about $700 you can get a telaire CO2 meter, a data logger and some software. Can pretty much give you the infiltration info you are looking for, can tell you when there is a big problem of too much outside air moving through the building. It does not find the leak source like a blower door does, but can give you a much more realistic idea of how much air moves through the building
Carnak, the GE telaire 7000 CO2 is a lot more affordable, & IMO would provide the data needed to locate general infiltration areas needing to be addressed.

I also believe that building codes should require that needed infiltration data be made a permanent record of every residential & small business building.

I personally don't believe that all those requirements including a manual J load calc should be piled on the HVAC contractor; they simply are not doing all those requisite energy efficiency things, & most won't do them. The building envelope should go more to the builder's & inspector's responsibilities.

The future is wide open for the contractors that will do all the requisite things including the airflow & ductwork testing & retro work.

All of our HVAC organizations should be pushing these Energy Conservation initiatives to the media, & in the media.

We should have our own programs on cable & satellite systems! The time is now & the time is right!

I get sick watching real estate & home remodel programs that only focus on the aesthetics & nothing on the practical monthly money savings home comfort & health aspects of their investments.

Watched a recent TV program where the real estate agent was showing a home in Vermont with electric baseboard heat all around the walls in every room & not a single question or a word about the heating costs in that climate.

Burlington, Vermont is a -12F at 99%; also, nothing said about the insulation, or past record of heating bills, etc.! - Darrell

[Carnak]

............double post

[Carnak]

telaire price included a data logger, a cable some software and some UPS shipping.

I have 3 of them

[susan2010]

UK Building Regulations 2006 Part L2A
Building leakage of 10 m³/hr.m² @ 50pa
(19.5 m² (area) x 10 m³/hr.m² (air tightness)) / (19.5 m² (area) x 4m (height)) = 2.5 ac/hr Infiltration rate
Hevacomp 2.5 ac/hr Infiltration for room 19.5m² = 1465 watts heat loss
Rule of thumb = 19.5 m² x 70 w/m = 1365 watts heat loss