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Comment by weaksauce | Hacker News Reader

If you have a smallish house and a centrally located fan, a whole house fan is amazing. The rooms get cooler and the attic gets cooler too. You can shut doors to make a specific room cool in minutes. Seriously one of the best things you can do to a house imo.

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My home isn't really set up for a whole house fan, but what I'd love to do is find some way to divert the HVAC blower fan to blow all of its output outside.

It should have the same net effect as far as I can see. I'm curious why systems don't have an option to do this.

Some do, but it's inefficient on a couple of levels. First, the damper to divert air to the attic will never seal perfectly (or at least it won't a short while after it's lived in your attic) so you'll always be losing some cooling to your attic when your AC runs. Secondly, the volume of air an AC system is set up to move does not come close to comparing with the amount of air a properly sized while-house fan will move. The blowers are just designed for 2 different roles...

Yeah, I realize the HVAC blower is smaller than an attic fan. It just seems like having a controlled diverter (blow air to the house /or/ blow air outside) could help draw in outside air when needed.

In my part of the country it cools off at night, but the wind typically stalls. At least drawing in some of that air could let me skip running the A/C compressor overnight.

Yes, but that doesn’t change the inefficiencies I mentioned, which are why it isn’t often done. It is done sometimes - I had a home with such a setup - but you’re much better off dropping a few hundred $$ on a proper whole house fan.

The attic getting cooler is one of the most important aspects of a house fan. The thermometer in my attic regularly reads 20° F above the outside temperature. Blowing that huge pocket of hot air out makes a huge difference.

If a hot attic is making your house hot, then you need additional sealing between the attic and the house, or additional insulation on the floor of your attic. Attic spaces are normally vented so that they are kept at outside temperatures. In the winter, attics are regularly 30 degrees below the inside temperature. A 20 degree difference in the summer shouldn't be a big deal. That said, plenty of people will sell you attic fans or other gizmos to moderate attic temperatures if you don't want to fix the insulation/sealing problems.

Whole house fans do help a lot in pulling cooler outside air into the inhabited spaces.

My last house had a hot attic with a window at each end - I always intended to set up four fans on relays, two in each window, so it could blow cool air in from either end, to take into account which side was cool and shady (and night they could just switch off to to reduce wear).

In case this ever comes up again... they have attic fans that are activated via temperature so that would your overnight issue and I'd imagine the gains by rotating which side is pulling in air is negligible compared to the effort to control it.

Before air conditioning became accessible, large window fans (like the Homart Cooler - which I own) were very popular in the middle of the country with hot days and cool night (e.g. St Louis).

Not as good as placing one in the attic, but a really effective alternative that can be carried from property to property.

"If you have a smallish house and a centrally located fan, a whole house fan is amazing. The rooms get cooler and the attic gets cooler too. You can shut doors to make a specific room cool in minutes. Seriously one of the best things you can do to a house imo."

I just added a whole house fan to my home in the bay area and it works very well - the temperature drops by as much as 30+ degrees from daytime to night time here.

I really appreciate the simplicity of not having AC infrastructure anywhere in my house.

However, I have lived in other climates, like Minnesota, where the nighttime temperature does not drop much at all and I am not sure it would be worth the effort. If it was a box to tick for new construction, then sure - but I wouldn't go out of my way to add it to a house after the fact ...

We have one whole house fan that cools 4700 sqft. During the day I turn on our mini-split in the theater and leave the door open. On the vast majority of 95F days the main HVAC doesn't come on at all. On days where it hits 100F, the main HVAC might kick on for an hour or so.

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