Mechanical ventilation of your home is a good idea. That means a fan running 24 hours a day 365 days a year. It provides a means of reducing indoor air pollutants and improving IAQ. It’s good for you and your whole family. We have a cute saying “dilution is the solution to indoor air pollution”


But aren’t you supposed to show me ways to save money and use less electricity? I don’t get it

True our goal is to save you money and we will show you how to use less electricity. Remember our goal is to address your safety and comfort and using methods of performance contracting and building science and our end result will be a more efficient home. Even though a fan will be running at all times these fans are very efficient and sip electricity rather than guzzle it. The benefit more than outweighs the cost.


Can’t I just open a window?

Sure you can it’s a good idea to open your windows.  We still want to mechanically ventilate your home to ensure it has fresh air at all times. We want to have control over our fresh air and not simply guess. You can open a window whenever you want but we still need ventilation.

Ok so now we have established you need ventilation. What kind and by what standard. The logical answer would be to use ASHRAE 62.2 2007 here in California s a guideline.  It is what the current California new home construction standard uses. There are some rebate programs that require other versions but we will stick with the referenced code.The formula below is watered down version

Let’s take a 2000 square foot four bedroom home as an example

The formula is pretty basic (sq ft * .01) + (bedrooms + 1 * 7.5)

(2000*.01 =)20 +37.5( =5*7.5)

So we need 57.5 cfm for our home.

So let’s get a 60 cfm fan right? Uuuummmmm probably not

The thing is that we want that amount delivered not close. The type of material used for ducting is important. The length of the run is important. How many elbows does it have is important. Proper sealing of ducts is important. Quality of the product is important.  Not accounting for these factors will have our 60 cfm producing 40 cfm or even less.

I would normally recommend that we take that size and add 15 percent and round up to the next available fan. I would recommend a 70 cfm fan in most cases for proper ventilation.


What about using more cfm would that be better?

Yesnomaybe is the answer.

Yes              It is better for IAQ

No               It is wasting Energy

Maybe       Every home is different and occupants are different. If you have 10 100 gallon fish tanks we might want to ventilate a bit more. There are other reasons as well. We call them when we see them.

For the most part we want to size according to the standards that is why they are there. We want size and install the system correctly and test it to make sure it’s providing you with what you need.


What kind of fan?

This is a good question and the answer can vary given different factors.


Balanced system’s which brings fresh air from outside and exhaust stale air from inside. Cost is the biggest issue with this style


Supply only ventilation which brings air from the outside. It puts the home under positive pressure (see does my house suck?) and ensure the air is fresh


Exhaust fans. These are already set up in many homes. The install and parts are more cost effective. However this air will be made up from wherever. Studies have shown that even though there is no control of where the air is pulling from that the air that it pulls in is better than the air in your home. This is the most common strategy not due to performance but due to price.

OK lets seal it tight and ventilate it right!

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Comment by Robert Riversong on September 4, 2012 at 9:46am

There is no one "right" approach for all climate zones. Here in the cold northeast, where most homes are not air conditioned in summer, we need 24/7 mechanical ventilation only in winter, and putting a house under positive pressure will almost guarantee moisture problems in the building envelope (since only exfiltrating air going from warm to cold will cause condensation).


I've been building super-insulated homes for 30 years and have always used a quality bathroom exhaust fan (Panasonic) with both manual timer switch for spot ventilation and 24-hour programmable timer for (dis)continuous ventilation to meet the ASHRAE 62.2 standard. Make-up air is provided by strategically located fresh air inlets in bedrooms and living areas and offices. I use Airlet 100 by American Aldes, but there are now a half dozen options from various manufacturers, including Panasonic, Reton, Condar and Therma-Stor.



Randy, I would suggest one of the Panasonic Whisper series bath fans, a Grasslin KM2-ST timer, and any of the passive inlet vents (avoid ones that are humidity or motion controlled). You must have an externally-vented kitchen range hood (only 100 CFM required) and bath fan to meet code and IAQ standards. And I would suggest considering venting the attic, which relieves moisture, minimizes summer radiant heat gain and prevents ice dams.

Comment by randy tolowski on September 1, 2012 at 2:48pm

Love it Glen, We have an attic. I am a carpenter by trade, neat won't be a problem I'm a cabinetmaker, easy I don't know the meaning of easy.(I would use screws with plugs to match the grain of the sash instead of nails). I'm open to the bath fan and kitchen hood. What is a good unit for the bath? Kitchen hood I'll find one, but what about fresh air intake? labor is free(labor of love). Also unvented attic r-60 no eaves(no overhang soffit). Local guys act like I'm speaking Martian. Fresh air is what I need. Any through the wall intakes worth considering?

Comment by Glen Gallo on September 1, 2012 at 2:25pm


What makes this business so interesting to me is regional differences. I would never encounter such a house here in Southern California. Snow is something we see on TV or drive hours to visit. Brick homes are about as common as common sense from a politician.(we see it but it is rare). Local guys will have a better ability to give recommendations. So from from my chair in Americas Finest City I would suggest the following

A saw, a hammer a screw gun possibly a grinder and some sweat possibly a roofer and a whole lot of creativity

I would say you have no choice but to find a way to install a Kitchen Fan and Bath fans and lastly if needed an HRV/ERV.

I can appreciate that they are not there. But we cannot  ventilate without ventilating. Is there a crawl space? Is there attic space? is there a wall? Are there cabinets? is there a place a chase could be installed.

None of the solutions for a project like your will be neat and easy from what you described. As Larry the cable Guy has often said in his act and is the  best piece of advice on television which rings true here "get er done"

If no to all of the above nail a window open on both ends of the home. (just kidding)

Comment by randy tolowski on September 1, 2012 at 1:25pm

Hi Glen, what would be your recommendation for a 1950ish cape cod brick with hydronic heat(radiators) with A/C window units. no bath exhaust, no kitchen hood exhaust. It's been sealed tight I'm trying to ventilate it right. Any suggestions would be greatly appreciated. I have a small 5" fan rigged into the upper sash for exhaust air from the kitchen. All suggestions will be tried out as I use our house as a test lab. I'm not asking for put in HRV/ERV because There are no ducts. In other words if walked into this situation at a clients home what would I suggest?

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