The more water you can store the easier temperature regulation will be. You could think about doing some aquaponics or just some tilapia or koi for fun? Those electric aquarium and farm heaters are actually really efficient at heating for winter since the water holds the temperature better than air.
I wonder if you guys can get away with evap coolers for greenhouses in seattle?
I bet so, at least in the summer when it’s bone dry, but since it’s rarely above the upper 70s I’m hoping just improved ventilation and maybe an intake and/or exhaust fan will suffice.
The rain barrels don’t put out enough heat to make a meaningful difference. I put several hundred gallons of water in my greenhouse and it made zero difference while taking up way too much room.
I think your going to need both intake and outtake fans for sure. Im going to go for the fans and cooling that fruitnut has and think your going to need more than you would think and will never be upset at having more than you need
The idea is a gallon of water holds 800 btu i believe?? So you need a lot and you would want it to serve a purpose. Usually people put tanks in the ground
I am thinking … hot tub !
That was actually the compromise i made with the wife to do the greenhouse addition!!!
I was like oh baby thats going to be expensive and you know we are going to have to spend more on the greenhouse to do that… 
Between my two barrels I have about 120 gallons, which I’ll be using for watering, so it’s definitely not just for heat purposes! I figured they are better inside than outside, and don’t take up a ton of space:
I just read that reply to my wife and she’s on board!
I think we are experiencing our own hundreth monkey effect 
I have A neighbor, off grid solar ,that Has a swimming pool / hot tub in a greenhouse , heated with water pumped through cooper coils in a wood stove and into the pool.
Last time I visited , a foot of snow on the ground,the water In the pool was almost to hot to get in.
He said a fire would keep it warm for days , had tropical plants floating in mud tubs in the pool. I want to do this …
I’ve thought about a pool in a greenhouse surrounded by mango, citrus, and banana. It can be set up here to be warm enough to swim all yr basically passive solar. And cool enough in summer to enjoy. No sunburn either…!! I noticed today that near noon the sun already seems basically straight overhead. 30 degrees north latitude will do that.
That’s something we never get to experience here at nearly 48°N! But at least now the shadows don’t stretch all the way across my lawn like they do at noon around the winter solstice.
Storing water makes considerable difference in keeping a stable temp.
It might not work for some, but it sure does for others.
It may not produce the heat needed for some plants,
and it may not produce summer cooling sufficiently…all depends.
But, daily high and low temperature swings are affected quite a bit in an unheated/uncooled greenhouse by the
storage of large amounts of water.
When I didn’t notice any difference despite all the water in my greenhouse I did the BTU calculations and figured I’d need something like 1/2 the volume of my greenhouse to be water to avoid dropping below freezing in the winter on an average day. Then I did some research into commercial greenhouses- you’d think they would take advantage of this water storage thing to save money- but none of them do water storage (that I could find). I searched the Internet too, looking for someone who could make it work. I struck out there also. If you know someone somewhere who made it work please share, I’d love to learn how they did it!
@PatapscoMike
At hidden springs nursery in Cookville Tn. They have a large greenhouse , south facing , north wall insulated and stacked with lots of 50gal. Barrels painted black full of water.
Seemed to be working, I remember some impressively large fig trees in there .
Could call Annie there and ask for details ?
Does anyone have suggestions for particular style of fans they use for intake or exhaust or both? The commercial ones for greenhouses are mostly very expensive and overpowered for my needs, but I want something that won’t leak air when it’s not running, so ideally I want something with a flap or valve integrated into it so maybe one of the cheaper ones there would work? I’m thinking maybe something intended for a HID grow tent might be another option, or basically any can fan might do.
There are some hydroponics/greenhouse supply places I haven’t visited yet around Seattle, so I might just do that in the next couple days, since we are having perfect weather for testing cooling, this is almost summer temperatures for us!
Today it’s very sunny and breezy, I decided to leave the greenhouse totally closed other than the roof vent. So far no extreme temperatures but still headed up:
I used the cheap chinese exhaust fans with louvers. for example this one. I assume they’ll need motor repair or replacement every few years but they’re pretty simple. the louvers aren’t perfect they do leak a little but they have foam on the tips so it’s not that bad. just some leaking at the sides maybe equivalent to a couple square inches of open space per fan
for my greenhouse, my temperature goal is just to “not freeze for 10 or 11 months a year” and so far I’ve been able to do that without any heater. meeting that goal is +3 months of growing season here with no added heat. I want my max temp to be low, 80-85, so cooling mist is necessary. from playing with it a little recently, 2-4gph of simple mist emitters in the intake path + 500 watts of fans are enough to hold near ambient temps in full sun
emitters like these. they’re a cheap alternative to a wet wall at least for my climate. but you can’t do too many because you’ll end up with droplets hitting the ground before they evaporate so your cooling capacity is limited
https://www.dripdepot.com/product/dig-0-8-gph-fogger-on-barb
After today’s closed doors test, I’m hopeful that even a small improvement in intake will be enough to deal with our summer temperatures on all but the hottest days, and on those days I’ll open both doors and windows. Leaning toward something a lot smaller, more like 600 to 900 CFM, which would be about 1/3 the price.
Have you had any issues with nozzles clogging up? That was my issue the one time I tried misters for an indoor garden. I also have no running water to the greenhouse, so I was hoping to use the gutter-fed rain barrels. Would likely need a good particulate filter on the pump if I use that water for spraying.
As I mentioned above, I didn’t open any doors or windows other than for brief moments today, with an outside high of 62°F and entirely clear skies it plateaued in the greenhouse around 93°F and has begun to drop:
The shadow of a large fir tree is just starting to pass the greenhouse, so I expect the temperature decrease will accelerate soon, at least until the roof vent closes:
You may notice the overnight bump on the chart above – I chickened out and turned the heater on, on high, before bed, and then turned it off first thing in the morning, so that’s a 1.5kW heater, but without circulation to mix the air (sensor is about 3/4 up from ground to roof peak, so ground was likely colder).
I haven’t had clogging problems. I use a 200 mesh filter in my drip system and it’s just municipal water to begin with. here’s the other emitter I’ve used, it’s quick and easy to clean, maybe this would be better if you expect clogs:
https://www.dripdepot.com/product/netafim-coolnet-pro-fogger-w-check-valve
as far as cooling needs… your goal is some delta temperature above the hottest summer day. if you’re holding +30 degrees that’s fine when it’s 62 out but when it’s 80 later in the summer you’d be at 80+30=110. our summers here get to 85-90 sometimes (and maybe a few days at 100) so I would be ok with holding to +5F, ideally less, which from my tests would need either 1-2kW of fans or my current 500 watts + mist (or other evap system)
I have a gigavent opener rigged with rope , pulley and a spring to louvers in the gable ends up high .
Works pretty good.
It’s not electric, one with the piston that expands when hot .
A suggested place in your house would be as high in your gable as you can , so that biggest framed opening top center , on the gable
End wall . Could put one on both ends ? Maybe add a low vent too, to give it the chimney effect .
I would go with the Schaefer’s since they are made in the USA and will last a lifetime.
Definitely expensive however.
You could do some smaller centrifugal fans like the ones used for radon mitigation and start with outtaking and add as you go.
the temperature activated louvers like hillbilly is talking about would help also.
