Several years ago, I read in a magazine, (Popular Mechanics,I think), of a homeowner who installed just such
a system. In certain parts of the country, usually in
spring and in autumn, there are days when the morning
sun, shining on a dark roof soon makes the air in the
attic warmer than the air in the house. A sensor then turns on a fan and blows the warm air down into the house to 'take the chill out' in the morning.

If your attic is vented (most likely is), then when the fan runs in reverse, you'll be pulling in outside air to replace the attic (warm) air.

In the off chance that the attic is sealed, then you would need to provide a return of household air.

In either case, you'll be pulling in particles of fiberglass or other insulating material. Nice.

V

sounds too good to be true?
because it is.
you would be introducing all the elements
from the attic into the living space.
particulate matter (insulation particles, dust,
any droppings from mice rats and birds just to name a few)
introducing the ambient humdidty would cause relative humdidty inside the house to increase also.
I remember as a kid growing up in houses with attic fans,
but now home dynamics have changed with forced air systems
like central systems.
you don't say what part of the country you live in,
but like stated above..when it is cold outside it is cold
in the attic, warm outside, hot in attic.
best of luck.

How about supplying a heat pump located on the outside of the house with warm attic air through a duct and shroud around the heat pump from the attic?

This is a very old thread, but in case anyone sees it, here is my solution to this free heat opportunity:

After air sealing and insulating my 530 ft condo, I continued to be irked by times in the heating season when the attic would reach 80-90deg, while the apartment was at 65. I finally ran some back-of-napkin numbers that showed that an ERV could be used to efficiently transfer attic heat into the conditioned space.

So I bit the bullet and gave it a try. I installed a RenewAire EV Premium L, (largest most efficient core) and ducted it so that the attic air and the conditioned air run separately thru the ERV. Basically, the ERV pulls room air up, heats it with warm attic air, and returns it to the room. MERV 13 filters are installed in both streams, and the attic insulation is covered with plywood/plastic which prevents it from kicking up dust. The ERV is controlled by two thermostatic switches in series, so that it comes on whenever the room is below 72, and the attic is above 72. In practice, this results in an starting temp differential of about 5 degrees minimum, since I let the apartment cool to 67 overnight. That differential quickly climbs as the sun shines.

Right now, for instance, at 1pm on a partly cloudy day, outdoor temp 67, attic temp 88, the system is intaking room air at 69 and returning it at 81, at a rate somewhere around 280 CFM. That comes to about 2400Btu/hr, and a “COP” of 4+, given a fan consumption of 170W. In the peak of a sunny day like yesterday, when the attic got up to 95, theoretical yield could be 5300Btu/hr, and “COP” close to 9.

This sometimes won’t be a sufficient heat source. But for the shoulder seasons in this temperate sunny climate, in a small well-insulated/sealed space, I’m guessing it will be all that is necessary. In fact, my “primary” heat source may become the supplemental one. I’m not sure how scalable this idea is, but for older buildings with an accessible clean attic and a well insulated attic floor, it seems possibly worth considering. Obviously it is not cost efficient at today’s energy prices. But it is extremely energy efficient, and taking a longer view of the future costs of GHG emissions, it seems an interesting way to partly solarize an older building. Based on my temp records, I think it will also be able do some cooling at night in the summer. Total materials were around $2500, plus my labor.

After seeing this comment above, I’ve decided to install S&P TR 130. Will update in a few weeks.

Also, to note, my understanding is that these ERVs (energy recovery ventilators) don’t mix air from the attic with household air. They exchange heat. So, presumably, the air quality shouldn’t be impacted.

We keep the house at 65 during the day and just put on a sweater. No wonder people have such high utility bills when they want summer temps indoors in the winter.

@ HU-517700865 Thanks for this info. It took some looking to find a thread addressing this scenario with a proper, studied approach.

At the moment I'm on the third day of an ice-induced power outtage. But today the clouds are mostly gone, and the sun is warming things up a little bit...which got me thinking about the warmer air in the attic...

Ugh, hope you get your power back soon!!⛄️⛄️⛄️