Ventilation

One thing about the Northwest, is that after 7:00 PM most nights in the summer, the outdoor temperature falls below 70 degrees. Many newer homes have built in ventilation devices controlled by a mechanical timer, like this 👇

These devices control an automatic damper that opens to the outside with a screen to keep out larger particles (birds, squirrels etc.).  Properly installed, the air is then drawn through the home’s filter system, mixed with house air and distributed. These systems, called “economizers”, are well known in commercial HVAC, and are currently required by code. The system fan comes on and this mixed air is used for cooling. There are limitations to this process, but it is often a much more economical way to get evening cooling. The cost of this system ranges from $800 - $1,500 installed plus tax.

Sometimes the addition of a much better filter system is warranted. Please see our article on filtering.

The damper looks like this 👇

The hood looks like this 👇

The hood is probably the most obvious part of the system. It can be painted to match the home and made less conspicuous, though people rarely look up, as they say.😉

There is also another version of the hood with a more flush look. All these components are connected with insulated duct to prevent heat transfer and sweating.

There is another newly popular device to provide fresh air to a home. It is called a Heat (or Energy) recovery ventilator. It uses a heat exchanger inside the body of the ERV to pass the incoming and leaving air streams past each other and partially temper the incoming air with the exhaust air. These devices have limitations. They try to make a humidity exchange as well, but only do a modest job at that. They also have filters that need cleaning to keep large particles out of the home. The idea is they provide a balanced pressure to the home. The amount of incoming air matches the outgoing air so the home has no extra air to deal with and no negative pressure. Every time you operate the kitchen or bath fan, or use the dryer, you vent out house air. The home must make up this air and lets it leak in from other vents and around windows and switches and wall gaps. ERV/HRV’s are designed to keep the air pressure in the house the same, whereas the ventilation system I first described pressurizes the home and it must leak out the extra air, usually through all the normal ventilation openings, fans and dryer exhausts. ERV/HRVs are expensive tools to exchange air in a home. If you have a very tight home, it can sometimes be necessary to add ventilation.

Recently I installed an ERV to a remodel project as specified by the architect. When all was said and done the client called me to discuss the operation of the ERV. I explained that she had an older, leaky home with some improvements like new windows but that she probably didn’t need to add ventilation.

One of my friends bought a new home and he didn’t have enough ventilation. Formaldehyde and other gases were concentrated from the construction materials and his wife developed chemical sensitivity. Apparently in some countries this is a known phenomenon and they leave the home vacant until the level tests low enough to be safe. We are developing and using a lot of low VOC materials now, but that is a recent development.

Many of the Washington state energy code requirements make adding an ERV an obvious choice, though frequently unnecessary. There is a technology called blower door testing. It establishes how leaky your home (or structure) is. If the value is more than 10 air changes per day, you probably don’t need an ERV. Leaky homes are not very energy efficient. I like the idea of a tight home, but not the idea that it needs ventilation or it might become unsafe to live in. So many of our modern conveniences create unintended consequences…

One significant problem is the addition of giant exhaust hoods for our upgraded stoves. I was helping one customer with some of his massive remodel project and noticed his Wolf brand stove was getting a large hood. I asked him what air capacity it had and he said 1,200 CFM (cubic feet per minute). That’s like removing the air from a 12 x 12 room and throwing it away every minute. I told him he might want to reconsider since he had a wood burning stove in the next room and it would definitely backdraft that and fill his house with smoke. Code officials are now requiring homes have a system to allow fresh air in to replace the exhausted air. This is a good thing. But you can see, running this fan for ten minutes would exhaust all the air in a 1,500 sq ft house. No wonder restaurants have trouble keeping the dining room comfortable!