My worst enemy

Is most usually Me, I have been thinking which is probably dangerous for me of a way to speed up and create a faster blower door than simply using in house exhaust fans such as dryers kitchen exhaust and bathroom exhausts.

My question is has anyone ever seen a high cfm fan mounted on a board or plastic that would fit into a standard door frame or window frame considered as portable that one person might carry to the job site to move large volumes of air quickly. I am in the process of pushing energy audits due to the high prices of fuel and or energy and have been thinking about fabricating such a device to move air but thought there might be one on the market already. Anyone have any knowledge of this.


I use one of those window fans that fit in like a window a/c unit. You can “suck” or “blow”.

I’m sure you have a manometer or a magnehelic laying around.

Why couldn’t you use a condenser fan motor assembly off an old outside unit. You would need to replace the motor with one that runs off 115 volts but that should not be a problem. I took the top of an old outside unit to build an attic gable vent fan once. Made the box out of duct board and code tape, mounted it in the gable vent (large round vent). I left the 230 volt motor in, it only pulls 1 amp. Put it on an inline thermostat. It would would dang near blow you hat off if you walked under the gable. It dropped the temp in that attic significantly and my cooling bill dropped along with it. I can go into the attic and work if necessary without too much discomfort whereas before I could not stay but maybe 5 mins. Point is, you can probably find everything you need right now. It already comes with a cage to cover the blades, plus it does not weight that much. I humped it up into the attic by my lonesome and mounted it.

Please let me know what you find Charley. I’m interested in that, too, but I’ve been so busy that time is short.:smiley:

Make the board from coroplast.
A corrugated PVC.
4x8 sheet sells for 8 bucks.

I googled blower door and found some for sale $2K to much for me I will build one. I have an old squirrel cage blower from a furnace that moves a ton of air I may look into Bob the builders Sheet of plastic for a base and cut it down to fit the door. Time is also my problem

I’ll let you know if I come up with any better ideas. :wink:

If its a Minneapolis door, the $2K may be worth it for its compactness and ease of set up.

If you are doing quanitative inspections, a professional door is a must. You don’t just want to create negative pressure, but a certain LEVEL of negative pressure.

I have a door, but I have found it is rarely needed for residential use.

Hope this helps;

I have ready excess to the gages and was considering a 3 speed motor and set it up with switches to manipulate volume of air. To me if one is charging good money for energy audits you should be as professional as possible. Just operating dryers and exhaust fans one has no way to actually determine the level of negative pressure just a guess and a whim.

Without a calibrated blower door and program, you can’t give the client any idea about how his house compares against some standard or norm. What are the Air Changes per Hour (ACH @ 50 pa) or the Equivalent Leakage Area (ELA) or the Normalized Leakage Area (NLA), etc.? You’ve got nothing to gauge the amount of air leakage against to tell the client whether a professional airsealing program (at many $$$) will be a good investment. If you’re using an energy audit program (as a class “A” auditor should), then you’ll need some air leakage data to complete the house picture…other than than it becomes a “garbage in/garbage out” situation

After about 1 year in the airsealing business in the early 1980’s, I was actually telling some homeowners after a blower door test that it wasn’t worth them hiring my services to reduce air leakage…the payback wasn’t there. That sure gets around in a small town!!

I would not even attempt to build or run a blower door without the proper training. Please if any of you build one and are in Southern California please call me when you do you first house with a fireplace!!!


Use a single speed motor and get a router speed controller so you can adjust your pressures more accurately.

[size=2]If you’re going to use a squirrel cage blower, it (the motor) does not have to go into a door or window opening. Leave the blower assembly in the house and connect it with flex duct to a supply air duct boot mounted on an adjustable panel to fit a window opening. You can easily install your magnehelic connections to get your airflow volume if necessary.

Those of you that are damning Charlie for making a blower door, he’s talking about using it to enhance qualitative thermal inspections not to determine quantitative leakage of the house.


As this thread illustrates, there are a lot of ideas that can be throw on the table
as to how to do an energy audit and what methods can be used to get there.

All the post I have read have some merit.

Now if you find out what the client expects vs what you supply, that is the key.

If you are not going to market you energy audit as an exact science, then
perhaps Will’s comments are a practicle middle ground to consider.

Also what does the client want.? Most really want to know where to spend
the bucks that give the most bang in return.

Brians comments come from what he experienced. Please tell us more.

BTW… this post is not bashing anyone.

Router speed controller will not work on a motor unless it is a “universial” motor.

Easy way to tell is it will have brushes

Most blower motors are not of the universial type


For a change John I agree with you;-) not trying to become a scientist just want to remove a little more air than the fixed appliances have the capability of doing.

As for the remark about the fireplace I was born at night but not last night:D

I have already observed the capabilities of these cameras and am wanting to exemplify the images by simply creating a higher degree of neg pressure. And No I don’t want to suck the ashes out of the fireplace.

I am of the opinion that all of us could learn more in this area. My intension is to build a blower door regardless and install it on numerous structures including my own home before I ever charge money for this service.


Thanks Charley good thread caused much thinking by all.
I am sure many got some new information and Ideas from this thread.

What you are talking about is a door fan test. They do them all the time on rooms that have gas systems for fire suppression. You use a manometer to measure pressure in the room obtained by the door fan. Call your local fire alarm company. They sell the fan and the computer program that will tell you how many leaks you have to seal up in the room to contain the agent.

Thanks Gary I was not aware that fire alarms companys also did basic blower doors I will have to check them out see what they have.

I just paid $2,650 for my Blower Door from a company in Canada, It’s called Retrotec. The new MN Blower Door was close to $3,200 with all the bells and whistles. You may find a Blower Door at a low price, but you need the software also, and that is not included in the prices. Every state has a energy standard table that you have to use. You need to find out what your state requires, and let the company know so you can purchase the right software for your tests. Before you buy this system shop around, there are a few companies that manufacture this equipment.