# Generator Shed Ventilation



## Bluwolf (Nov 8, 2020)

New member here but I've been lurking for a couple weeks. I live in southwest Florida. After hurricane Irma my wife decided we had to have a generator (I had been saying that for a couple hurricanes but I digress). 

I decided on a Champion dual fuel model 100296 





7500-Watt Dual Fuel Generator - Champion Power Equipment


Powering Your Life




www.championpowerequipment.com





I used the L14-30 plug into a inlet box, then into the main breaker panel with an interlock setup.

I built a shed out of a Suncast BMS 4700. See pictures below. When the generator is in use (only twice since the build, for only a couple hours each time) the gas tanks and the shelf they're on are removed. The propane tanks are spread apart exposing the large vent behind them. There is a small double fan unit placed in front of the vent, between the propane tanks. On the other side is a 1320 CFM attic fan. The whole set up is on the side of the house that is in the sun all day long. This was the only location I could put it and have a reasonably short cable length to the inlet box. 

My question is, is this set up sufficient to cool the generator for an extended amount of time? I have other questions, and there are other details, but I'll just post this and see what comes back.

Thanks for your time.
Mike


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## jkingrph (Sep 18, 2017)

My first thought was that the gas tanks above the generator was a fire waiting to happen, then you said they are removed during use. Is your fans inlet or exhaust? At that level I think inlet would be best, and would add an exhaust vent up high over the generator, taking advantage of gravity, hot air rises, pushing cooler air across the generator then out the upper level as it is heated. Even if it is one of those combo fans one in/one out I think you would get more heat buildup.


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## drmerdp (Apr 10, 2018)

I build 2 operating enclosures from sun cast sheds, they are nice starting points. I like the shelf for gas jugs while the generator isn’t in operation. Personally I’ve kept the intake low and exhaust high but you shouldn’t have any issues As long as the fan is adequate. What’s that fan CFM rating? With the doors closed things heat up very fast and the plastic heat soaks quickly. I used foil faced foam board to create a temperature neutral space and it worked very well.

Where does the exhaust exit? My old champion exited toward the back wall. I ended up building an exhaust system and wrapped it in header wrap. If you don’t build an exhaust, make sure to use adequate heat shielding. The alternator and engines cooling system also exits the back, so heat shielding is very important.


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## Bluwolf (Nov 8, 2020)

Thanks for your replies. I'll try to answer them in order. 



jkingrph said:


> My first thought was that the gas tanks above the generator was a fire waiting to happen, then you said they are removed during use. Is your fans inlet or exhaust? At that level I think inlet would be best, and would add an exhaust vent up high over the generator, taking advantage of gravity, hot air rises, pushing cooler air across the generator then out the upper level as it is heated. Even if it is one of those combo fans one in/one out I think you would get more heat buildup.


There are 2 fans, one at the vent on the left (not shown), drawing air in, and the attic fan on the right, being the exhaust.
There are also 2 vents in the doors up high (that I don't have a picture of). Hopefully doing what you suggested and venting heat at the highest point in the shed.





















drmerdp said:


> I build 2 operating enclosures from sun cast sheds, they are nice starting points. I like the shelf for gas jugs while the generator isn’t in operation. Personally I’ve kept the intake low and exhaust high but you shouldn’t have any issues As long as the fan is adequate. What’s that fan CFM rating? With the doors closed things heat up very fast and the plastic heat soaks quickly. I used foil faced foam board to create a temperature neutral space and it worked very well.
> 
> Where does the exhaust exit? My old champion exited toward the back wall. I ended up building an exhaust system and wrapped it in header wrap. If you don’t build an exhaust, make sure to use adequate heat shielding. The alternator and engines cooling system also exits the back, so heat shielding is very important.


The CFM is 1320 on the attic fan. It might be hard to tell from the pictures but there is cement board across the back of the shed. Like your Champion, mine exhausts out the back. I cut a large square out of the plastic to keep the exhaust heat away from the plastic back wall. Then cut a round hole through the cement board the same size as the exhaust vent that goes over the end of the exhaust pipe. Then used a piece of cement board to cover the square hole and mounted the exhaust vent to that. The idea being that only the cement board touches any part of the exhaust and hopefully keeps all the plastic away from heat.

I also have a remote thermometer that I can place in the shed and read from indoors. But I wouldn't mind suggestions on where in the shed to place it, so as to get a good sense of the situation in the shed.


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## jkingrph (Sep 18, 2017)

I was not familiar with the "shed" you listed. I just looked it up and see it is 70 cu feet in volume. With a 1310 cu foot fan, using as a exhaust you would change the air 18.9 times per minute in an empty shed. Take the volume of your gen and two propane tanks and it might exchange 25 times a minute. At that rate I would think the exhaust fan only with an adequate size intake opening would be enough. Just be sure to shield the exhaust especially where it exits the plastic walls, and also maybe something like a piece of concrete fiberboard between the generator and the plastic walls to help with radiant heat. I wish I could do something like that with mine, but the way the house is made, my meter box is at a front corner by the garage, and no place to put something like that except in the front yard which I prefer not to do.


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## tabora (Sep 6, 2018)

I used a SunCast BMS2500 shed with a 16" 1,200CFM iLiving ILG8SF16V Exhaust Fan on the right side; the generator is turned so that the exhaust faces the bottom of the fan and exhausts with the airflow. There is a 17" 5NKN4 Dayton gravity operated inlet shutter on the left side. I have a thermal remote monitor mounted top center on rear wall, and a second one mounted outside on the propane tank. The internal alarm is set at 80F and has never gone off in 3 years of operation (about 60 running hours so far).


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## Bluwolf (Nov 8, 2020)

jkingrph, I don't know if you can see my pictures, but they show how I used the cement board on the back wall, and how I accounted for the heat of the exhaust passing through the back wall. Judging by your math I think I should be alright. I was concerned that here in southwest Florida when hurricane season is, is also some of the hottest times of the year. AND the shed is always in direct sun during the day, which is brutal down here.

tabora, I see you live in Cape Elizabeth. I lived there 50+ years ago when my father worked at the Portland Airport, it's a beautiful area. Does your gen get used in the summer, or is it mostly winter running? I remember the winters up there and could see you getting a good bit of use during the winter. I'm concerned because the days can be 95 degrees with a heat index up to 110. In other words I'm starting at 90+ degrees before I even start the generator.

Thanks for the replies,
Mike


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## tabora (Sep 6, 2018)

Bluwolf said:


> Does your gen get used in the summer, or is it mostly winter running?


It's been mostly summer/fall (hurricane/wind storm seasons). The airflow through the box is so great that the temperature inside is lower than outside except during winter. Have not had to use it in winter yet (fingers crossed), just exercising it.


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## drmerdp (Apr 10, 2018)

For Florida heat you’ll need a lot of airflow. I recommend a load test, at the generators rated amps before settling. Run it long enough to heat soak everything and monitor the internal temps.


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## iowagold (Jan 22, 2020)

Bluwolf said:


> jkingrph, I don't know if you can see my pictures, but they show how I used the cement board on the back wall, and how I accounted for the heat of the exhaust passing through the back wall. Judging by your math I think I should be alright. I was concerned that here in southwest Florida when hurricane season is, is also some of the hottest times of the year. AND the shed is always in direct sun during the day, which is brutal down here.
> 
> tabora, I see you live in Cape Elizabeth. I lived there 50+ years ago when my father worked at the Portland Airport, it's a beautiful area. Does your gen get used in the summer, or is it mostly winter running? I remember the winters up there and could see you getting a good bit of use during the winter. I'm concerned because the days can be 95 degrees with a heat index up to 110. In other words I'm starting at 90+ degrees before I even start the generator.
> 
> ...


start with a metal shed.
then line with cement board.
use lots of powered ventilation.
and external exhaust
click here for the gen shed page.
there is at least one with metal.


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## Bluwolf (Nov 8, 2020)

tabora said:


> It's been mostly summer/fall (hurricane/wind storm seasons). The airflow through the box is so great that the temperature inside is lower than outside except during winter. Have not had to use it in winter yet (fingers crossed), just exercising it.


Temperature lower than outside... Well that gives me hope. If I can even get close to that I'd be happy. I will try the thermometer where you suggested, up high and in the center. 



drmerdp said:


> For Florida heat you’ll need a lot of airflow. I recommend a load test, at the generators rated amps before settling. Run it long enough to heat soak everything and monitor the internal temps.


I run the gen every 6 weeks, for about 20 minutes to a half hour. I'm not due again for a couple weeks but I might move it up to this coming weekend and give your plan a try. I also have an infrared temp gun. I've used it before but it gives different readings all over the place depending on where I was aiming/checking. In the end it left me with more questions than answers because I didn't know which readings to pay attention to. If anyone has any opinions on that I'd be happy to listen.



iowagold said:


> start with a metal shed.
> then line with cement board.
> use lots of powered ventilation.
> and external exhaust
> ...


All good suggestions. But one, I've already spent a good bit of money on the set up I've got. And two, the metal sheds don't hold up very well down here. The humidity turns them to piles of rust pretty quickly. The plastic ones hold up pretty well but again, the sun is rough on everything. I keep a tarp over it all the time to keep the direct sun off. That works well. The shed looks brand new underneath. And you know it's working because the tarps get sun rotted pretty quickly. I've gone through quite a few of them in the year and a half or so that the shed has been built.

Mike


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## iowagold (Jan 22, 2020)

use the good rubber roof coating on the metal!
yea the sun is killer here in the last few years!
bakes any good finish right off.

they make cement board siding...
you might look at that stuff.
and it comes in colors.
just make sure you wear a mask as the material is nasty dusty when you cut it.


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## wingless (Oct 29, 2019)

The Operation Manual for my portable generator (similar to those shown here) specifies 5' clearance on all sides (including above) during operation. 

The Operation Manual for that Champion 9375 generator (linked below) specifies 3' all around clearance and 5' clearance to combustible materials.



https://www.electricgeneratorsdirect.com/manuals/champion-3ded2e47d24f547114087fa31b5e9a24.pdf



My setup permits interior storage and partial protection during operation. After the hurricane passes frequently it is sunny and warm. Plus the generator will tolerate rain, if required.

My generator is stored after the engine running until stalled from the fuel shutoff, then the carburetor bowl manually drained dry. The fuel tank is also manually drained dry. This has been working fine for me for years.


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## tabora (Sep 6, 2018)

Bluwolf said:


> Temperature lower than outside... Well that gives me hope.


Yeah, I thought there was something wrong with the thermal sensor at first... The SunCast BMS2500 is 34 cubic feet empty and is probably about 28CF in use, and the fan replaces that much air close to once a second, so not a lot of thermal buildup.


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## Bluwolf (Nov 8, 2020)

tabora said:


> Yeah, I thought there was something wrong with the thermal sensor at first... The SunCast BMS2500 is 34 cubic feet empty and is probably about 28CF in use, and the fan replaces that much air about once a second, so not a lot of thermal buildup.


So, is it possible that having more cubic space in my shed ( thus more air to remove) is making it harder for my fan to change out the air inside or am I over thinking this again? I don't think I'm going to run out and get a new shed but it would be something to keep in mind when I'm trying to deal with the heat problem.


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## drmerdp (Apr 10, 2018)

No need for a New shed. My old champion 7000/9000 ran fine in summer heat in an old sun cast shed with a high velocity 16” exhaust fan and 24x18 intake vent.... with the addition of reflective insulation. Interior temps were well controlled.

Just in case I added a thermal switch in the low oil sensor wire to shut down the generator if temps got out of control. I also monitored temps with a wireless thermometer.


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## jkingrph (Sep 18, 2017)

Bluwolf said:


> So, is it possible that having more cubic space in my shed ( thus more air to remove) is making it harder for my fan to change out the air inside or am I over thinking this again? I don't think I'm going to run out and get a new shed but it would be something to keep in mind when I'm trying to deal with the heat problem.


I rather doubt that more cubic feet would be detrimental. Ideally you would have an exhaust fan higher than the generator/engine you are wanting to cool and an inlet opening on the opposite side so incoming cooler air would be sucked over/through the generator. Someone said temp inside his box was cooler than outside air and with an engine running in that box I have a hard time understanding how it could possibly be cooler.


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## tabora (Sep 6, 2018)

jkingrph said:


> Someone said temp inside his box was cooler than outside air and with an engine running in that box I have a hard time understanding how it could possibly be cooler.


Again, because the entire air contents of the shed are being replaced close to once a second with fresh outside air... Wind chill! If I calculated it correctly, the air is moving at about 214.86 linear feet/minute.








I have these remote thermal sensors inside and outside of the shed, with an alarm set to trigger at 80F on the inside sensor. It has never gone off, and often the temperature inside shows lower than the outside.


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## iowagold (Jan 22, 2020)

and there are now blue tooth sensors for temp as well as wifi.
as long as your fans are of good quality and designed for long runs in heat you will be ok.
and variable speed temp controllers for the fans rock!!


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## jkingrph (Sep 18, 2017)

tabora said:


> Again, because the entire air contents of the shed are being replaced close to once a second with fresh outside air... Wind chill! If I calculated it correctly, the air is moving at about 214.86 linear feet/minute.
> 
> 
> 
> ...


I do not think wind chill applies to inanimate objects, An inanimate object will cool faster with air moving over it as opposed to still air


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## tabora (Sep 6, 2018)

jkingrph said:


> I do not think wind chill applies to inanimate objects, An inanimate object will cool faster with air moving over it as opposed to still air


Yeah, I know that's the "reality", but still the temp reading inside the shed with the extreme air flow going over it is a bit less than the temp reading outside in the sun where the air is relatively still.


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## jkingrph (Sep 18, 2017)

Still does not sound right. How are you determining outside temperature I just checked standards and the themometer should be 5 feet above ground in the shade and over a grassy or dirt surface. Too close to ground gives heat from ground, and pavement will give elevated reading also. It should also be place so there is "adequate"ventilation around it


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## tabora (Sep 6, 2018)

jkingrph said:


> How are you determining outside temperature


Honestly, it's not a big deal, just an odd-ball observation. And to repeat, it's not always that way. As clearly shown in post 18, I use a wireless monitor with two sensors. One is mounted inside the shed on the center of the back wall about half way between the top of the generator and the roof. The other is mounted outside the shed above and in front of the intake or on the propane tank valve guard if propane is being used. I tried swapping them when I noticed the anomaly and the result was still the same with the measurement in the shed being a degree or two below the one outside in the sun as mentioned.


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## jkingrph (Sep 18, 2017)

Gotcha, I basically have two of those wireless moniters, ie inside outside temp/ weather units. Same outside sending units and they register different temperature at same location.


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## tabora (Sep 6, 2018)

Big windstorm last night - power went out about 11:30PM. The generator is purring in its shed this morning... I did not bother with the thermal sensors, but anecdotally:

After three hours, I went out and checked the ambient temperature at 12PM = 51F.
Held my hand in front of the exhaust fan; very cold air coming out the top and barely warmish air coming out the bottom where the engine exhaust is.
Opened the shed and put my hand on the fuel tank; stone cold.
Put my hand on the generator shed back wall as far down as I could reach; stone cold.


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## iowagold (Jan 22, 2020)

yea i was thinking of you tabby!
we were ok here in that blast.
but it sure was windy at times.. over 50 mph.
I delayed a couple of jobs...
way too windy to be on the road!
they had over 200k out of power est up your way.
darn Y3K!! lol!


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## Bluwolf (Nov 8, 2020)

tabora said:


> Big windstorm last night - power went out about 11:30PM. The generator is purring in its shed this morning... I did not bother with the thermal sensors, but anecdotally:
> 
> After three hours, I went out and checked the ambient temperature at 12PM = 51F.
> Held my hand in front of the exhaust fan; very cold air coming out the top and barely warmish air coming out the bottom where the engine exhaust is.
> ...


Did you run it through the night? Chances are, here it would be quite warm if we were to lose power. The wife would like to run the portable A/C to sleep more comfortably. Any problem with doing that?


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## iowagold (Jan 22, 2020)

Bluwolf said:


> Did you run it through the night? Chances are, here it would be quite warm if we were to lose power. The wife would like to run the portable A/C to sleep more comfortably. Any problem with doing that?


just make sure the gen is located in a good spot,
and locked up!!
GRIN!
you would be surprised at how fast they can run if they are not hobbled!!
lol!
yea the port ac units rock when you are out of power..
you can run them on smaller gens.
helps to keep the humidity down so you can breath.


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## tabora (Sep 6, 2018)

Bluwolf said:


> Did you run it through the night?


No, we were on the way to bed when it went out and it was blowing HEAVY rain sideways at 50MPH, so I just left it until morning. I started it up a little after 8AM and ran it until about 12:30PM when the utility power came back on.


Bluwolf said:


> The wife would like to run the portable A/C to sleep more comfortably. Any problem with doing that?


Only that it annoys the neighbors! Not mine, since it's in the shed, but several other folks were running screaming loud Champions in their driveways (several without any rain covers, even).


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## Bluwolf (Nov 8, 2020)

iowagold said:


> just make sure the gen is located in a good spot,
> and locked up!!
> GRIN!
> you would be surprised at how fast they can run if they are not hobbled!!
> lol!


It's in a shed behind a 6 foot privacy fence. With a motion sensor floodlight over it and one right across from it on the neighbor's house. Oh, and my very large dog who prefers to sleep outside and doesn't like anything or anyone in his yard. Besides, if they want to steal a gennie there would be several that would make easier targets.



tabora said:


> Only that it annoys the neighbors! Not mine, since it's in the shed, but several other folks were running screaming loud Champions in their driveways (several without any rain covers, even).


Well, most of the neighbors also have generators but I'm the only one with a shed setup. So, like you, they're the loud ones.

My favorite generator story... A couple months after I finished the shed we lost power from a transformer blowing up. As I mentioned most of the neighbors have gennies. But nobody keeps gas around. And nobody else has a gennie that runs propane. As I was getting ready I could hear some of the neighbors coming out to see if anybody knew what was going on. The wife still didn't grasp how the whole set up worked. She just knew I told her we'd have power if there was an outage. 

In less than 10 minutes I was up and running. Lights in the house, the TV was on and she was watching the news to see if there was anything about the outage. I walked outside and the whole street was dark and neighbors walking around with flashlights. Then my wife came out, looked up and down the street, then turned around and looked at our house all lit up. The look on her face was priceless, worth every penny and all the time I spent researching and building the setup.


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## iowagold (Jan 22, 2020)

Bluwolf said:


> It's in a shed behind a 6 foot privacy fence. With a motion sensor floodlight over it and one right across from it on the neighbor's house. Oh, and my very large dog who prefers to sleep outside and doesn't like anything or anyone in his yard. Besides, if they want to steal a gennie there would be several that would make easier targets.
> 
> 
> 
> ...


yup but the down fall is the lights are a tell tail...
yea i suffer from the same issue...
except mine is quiet!
GRIN!


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