What cheap fans can I use inside a greenhouse for drying firewood?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

ionalexaai

New Member
Oct 22, 2021
5
Ro
Hello from Europe.
I've been reading this forum for the last 5 years. I've built a greenhouse to dry firewood after seeing someone here do it.
While I'm happy with the results, this year I bought firewood way too late. It's pretty close to being green.

I want to speed things up a little by installing some fans inside the greenhouse. The problem is I don't have a lot of budget.
What I was planing was to buy some cheap box fans to put them on the top to move air around much faster.

The problem I'm facing is that I'm not sure if those can handle high temps when the sun is up. Max temp I saw is around 60 celsius.
Will those plastic box fans stand that much temp + uv + humidity inside the greenhouse?

I'm planning to just recirculate hot air inside, no extraction/exhausting air from outside. Some air exchange happens naturally because of the way the doors close imperfectly.

What do I need to know? Anyone using cheap fans inside their greenhouses to do this?
Thank you in advance for any help I might get.
 

mcdougy

Minister of Fire
Apr 15, 2014
790
ontario
Probably 60 Celsius near the top? If a fan is placed on or near the bottom your Temps may be much less?? I'm thinking for cheap you could try a box fan and probably be fine.
 
  • Like
Reactions: ionalexaai

trueg50

Member
Dec 19, 2014
26
VT
A relative of mine put an inexpensive solar panel on his drying shed and wired it to 2 (maybe more) banks of 120mm fans (I want to say 4x fans per bank). These fans are pretty standard fare industrial computer fans that can be bought for very cheap. These were mounted blowing down at about 10-12 feet off the ground. With the open design, south facing exposure, some air movement, and clear plastic doors the would dried very quickly
 

stoveliker

Minister of Fire
Nov 17, 2019
4,353
Long Island NY
Hello from Europe.
I've been reading this forum for the last 5 years. I've built a greenhouse to dry firewood after seeing someone here do it.
While I'm happy with the results, this year I bought firewood way too late. It's pretty close to being green.

I want to speed things up a little by installing some fans inside the greenhouse. The problem is I don't have a lot of budget.
What I was planing was to buy some cheap box fans to put them on the top to move air around much faster.

The problem I'm facing is that I'm not sure if those can handle high temps when the sun is up. Max temp I saw is around 60 celsius.
Will those plastic box fans stand that much temp + uv + humidity inside the greenhouse?

I'm planning to just recirculate hot air inside, no extraction/exhausting air from outside. Some air exchange happens naturally because of the way the doors close imperfectly.

What do I need to know? Anyone using cheap fans inside their greenhouses to do this?
Thank you in advance for any help I might get.

Recirculating moist air is not the way to dry your wood quickly.
I'd put fans on a timer, and let them exhaust to outside for 15 minutes every hour. The air will heat up, get humid, exhaust, and repeat.
 

ionalexaai

New Member
Oct 22, 2021
5
Ro
Recirculating moist air is not the way to dry your wood quickly.
I'd put fans on a timer, and let them exhaust to outside for 15 minutes every hour. The air will heat up, get humid, exhaust, and repeat.
I went from the assumption based on research that stated that recirculated moist air with 100% RH will get wood to 28%. Since now it's probably at 60% or more, that would still be a win for me.

But I understand your point of view.

So are you advising me to just put a small fan on a timer on one of the sides and exhaust every X minutes or based on temps? In this case, even a PC cooler would suffice.

Any other thoughts about the fans?

If I put them on the ground, they might not recirculate the hot air from the top.
Just thinking out loud.

Thank you for the replies
 

stoveliker

Minister of Fire
Nov 17, 2019
4,353
Long Island NY
Yes. At the top. Then you'll replenish it with dryer air from the bottom.

There are threads here about solar kilns. Check them out.

And 28% is not really dry enough. depending on your stove (age), I'd I'm for under 20% for best and safest performance.
 
  • Like
Reactions: patrickk222

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,164
Woolwich nj
I went from the assumption based on research that stated that recirculated moist air with 100% RH will get wood to 28%. Since now it's probably at 60% or more, that would still be a win for me.

But I understand your point of view.

So are you advising me to just put a small fan on a timer on one of the sides and exhaust every X minutes or based on temps? In this case, even a PC cooler would suffice.

Any other thoughts about the fans?

If I put them on the ground, they might not recirculate the hot air from the top.
Just thinking out loud.

Thank you for the replies
You will not need to use the fans for exhaust. Your greenhouse should have vents on it. You should have ridge vents as well as a side wall vent for fresh air. My greenhouse has automatic vent openers both top and side so when the inside temperature gets to 80 the vents will automatically open. My greenhouse is also equipped with a small solar array which powers a DC attic fan its a 12 inch and provides enough air movement. As the temperature in the greenhouse rises its ability for it to hold moisture increases. It may be 82 degrees out and 80% humidity but inside the greenhouse its 100 and 20% humidity even though the air coming in is at 80%most likely.. you won't need the fan to move air if you set up is right.
 

hickoryhoarder

Minister of Fire
Apr 5, 2013
711
Indiana
Excellent thread. I'm learning here.
 

ionalexaai

New Member
Oct 22, 2021
5
Ro
You will not need to use the fans for exhaust. Your greenhouse should have vents on it. You should have ridge vents as well as a side wall vent for fresh air. My greenhouse has automatic vent openers both top and side so when the inside temperature gets to 80 the vents will automatically open. My greenhouse is also equipped with a small solar array which powers a DC attic fan its a 12 inch and provides enough air movement. As the temperature in the greenhouse rises its ability for it to hold moisture increases. It may be 82 degrees out and 80% humidity but inside the greenhouse its 100 and 20% humidity even though the air coming in is at 80%most likely.. you won't need the fan to move air if you set up is right.
I do have ridge/gable vents on both ends. It helps move the air out naturally with just a little bit of wind.

My concerns were how can I speed up drying, considering it's november.

I know the wood will dry out in a few months, I just wanted to get it to at least 30%. Right now it's green wood, maybe even 60%.
There's not much sun going on, and the little sun I do get, wanted to use it efficiently. Hence, the fans.

Never considered placing side vents. I could just add some, but I don't see it helping, it will just cool down the greenhouse more.
Summer gets very hot here, the greenhouse passes 75 celsius easily in july/august.

How long do you have the attic fan for? How is it handling the sun/UV/heat/etc?

I can move around half a cubic meter of wood inside my tehcnical room where the gasification boiler is. I remember one year when I put a fan to blow air on the wood, it started cracking in jut a day. In 3 days it was perfect for burning.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,164
Woolwich nj
I do have ridge/gable vents on both ends. It helps move the air out naturally with just a little bit of wind.

My concerns were how can I speed up drying, considering it's november.

I know the wood will dry out in a few months, I just wanted to get it to at least 30%. Right now it's green wood, maybe even 60%.
There's not much sun going on, and the little sun I do get, wanted to use it efficiently. Hence, the fans.

Never considered placing side vents. I could just add some, but I don't see it helping, it will just cool down the greenhouse more.
Summer gets very hot here, the greenhouse passes 75 celsius easily in july/august.

How long do you have the attic fan for? How is it handling the sun/UV/heat/etc?

I can move around half a cubic meter of wood inside my tehcnical room where the gasification boiler is. I remember one year when I put a fan to blow air on the wood, it started cracking in jut a day. In 3 days it was perfect for burning.
you need a side vent. you need fresh air to replace the moisture laden air.. It wil cool the greenhouse some but it will also aid in drying as the fresh air will be drier. As far as the fan goes, its an attic fan, its Meant to be in the heat. Its the combination of warmth and dry air that is going to speed up drying, one with out the other will hamper your progress. Its mid fall and winter is approaching. The sun angle is low, so trying to speed things up is a useless cause. The sun is what is operating the kiln/greenhouse. you have only a certain amount of energy given to you now, you can't force it. It will dry but slower, its not summer. I started a mini kiln recently. I know it will season the wood, its just going to take a little longer You need a side vent 18/24 inches off the floor and a fan won't hurt, 6 inches off the floor. Id add 1 side vent look up greenhouse automatic vent opener, no electricity needed they are temperature activated put them on all the vents
 

Poindexter

Minister of Fire
Jun 28, 2014
2,560
Fairbanks, Alaska
As long as you can keep the temperature in there above freezing the wood will keep drying. I use passive ventilation only in my kilns, an opening maybe 20cm in diameter up high on a wall, for each cord of wood enclosed. One cord is "about" 2 cubic meters"

Once your overnight lows are dropping below freezing inside the greenhouse the wood drying is goign to slow down a lot, and once it stays frozen the moisture is not going to change measurably until spring.
 

Poindexter

Minister of Fire
Jun 28, 2014
2,560
Fairbanks, Alaska
Late October is a pretty late start, but I am not clear on where in Europe "Ro" might be. In Portugal you have a chance, in Denmark not so much.
 

ionalexaai

New Member
Oct 22, 2021
5
Ro
Hehe, Ro as in Romania.
Still getting some sun these days. Not like summer, but it's decent.
Some wood started to crack on the ends, it's a good start. Going to be a hard winter with this wood haha
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,164
Woolwich nj
Hehe, Ro as in Romania.
Still getting some sun these days. Not like summer, but it's decent.
Some wood started to crack on the ends, it's a good start. Going to be a hard winter with this wood haha

You need to check that wood with a moisture meter.. split it open and test on fresh split face and pins with the grain
 

ionalexaai

New Member
Oct 22, 2021
5
Ro
You need to check that wood with a moisture meter.. split it open and test on fresh split face and pins with the grain
don't have a moisture meter, but I just checked a few with a digital multi meter after a thread I saw here
most of them read 1.3 mega ohms. according to OP, it should read 3.2 to be in the 20% range
it's mostly fresh cut, just 10 days in the greenhouse
still getting condensation on the walls

i have a gasification boiler, so it will still burn, just not as desired
thought running some fans on the wood will speed things up, seems i was mistaken
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,164
Woolwich nj
don't have a moisture meter, but I just checked a few with a digital multi meter after a thread I saw here
most of them read 1.3 mega ohms. according to OP, it should read 3.2 to be in the 20% range
it's mostly fresh cut, just 10 days in the greenhouse
still getting condensation on the walls

i have a gasification boiler, so it will still burn, just not as desired
thought running some fans on the wood will speed things up, seems i was mistaken
on Amazon for like 20 bucks.. takes the guess work out
 

stoveliker

Minister of Fire
Nov 17, 2019
4,353
Long Island NY
Even then, did you use it on a freshly split surface (as in split the minute before you measure)?
 

woodsmaster

Minister of Fire
Jan 25, 2010
2,885
N.W. Ohio
don't have a moisture meter, but I just checked a few with a digital multi meter after a thread I saw here
most of them read 1.3 mega ohms. according to OP, it should read 3.2 to be in the 20% range
it's mostly fresh cut, just 10 days in the greenhouse
still getting condensation on the walls

i have a gasification boiler, so it will still burn, just not as desired
thought running some fans on the wood will speed things up, seems i was mistaken
Fans will definitely speed up the process. The first week or so your definitely going to want so good ventilation to get the moisture out of the greenhouse… after the humidity goes down to a normal level the fresh air is not as big of deal.
 
  • Like
Reactions: ionalexaai

FTG-05

Feeling the Heat
Feb 8, 2014
409
TN
I've had a cheap box fan in my attic in my house in north AL. It lasted for just under 20 years that I lived there. It was still working when I moved summer 2014.