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Discussion Starter #1
My attic train room is insulated, but only with R11 and R7.5. There is no permanent HVAC, but in the winter, I use a 1500-Watt space heater and for the summer I have a 15” gable end fan. They will make the space livable on all but the coldest or hottest days.

I thought about getting a Friedrich portable AC, but portable AC units are not efficient and that would require putting holes in the roof. Since the third floor staging area is next to the train room and I already have a hole in the wall between them, I decided to get an 8000 BTU window unit for the staging area and a Broan 380 CFM room to room fan. I made a box for the room to room fan to make it portable.

I’ve only used it a few times, but it does help. Makes the train room livable on days when it definitely would not be if I was using the gable end fan. It slowly lowers the temp in the attic and it drops the humidity so it is comfy in the train room. It works best if I set the AC in the mid 60s.

On sunny days when the outside temp goes above 90, I probably won’t use it, but I have bought myself a lot more summer train time with this setup.

Attached pics show the conditioned air inlet from the staging area to the train room and the Broan fan that pulls air from the staging area to the train room.

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I have limited experience with portables. but in fact I have a new one -- bought during a hvac redo recently. anyway i got it at a best buy 20 ish miles away because there were literally none in the surrounding nearby big box stores at that time. it's a name brand, can't recall which one. solid, kinda heavy but not rated for a particularly large space though. something comes to mind --they make combo ac/heaters portables also ... interesting idea there for your space.. anyway pretty big market, lot of options -- various sizes, price points.

But as you suggest, the heat hose has to go somewhere. In your case another option would be to run a long duct (pvc pipe seems it would work) through your fan portal and out the 3rd floor staging room window. you could have both!

(unit is somewhat noisy)
 

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Discussion Starter #3
Some of the portable units I looked at could be used as a heat pump or an A/C, but the more I looked at them and at window units, the portable units were just too inefficient. They actually made a new rating system to reflect the actual BTU for them. The single hose units are especially inefficient. I’m sure there are some applications where they would be the choice, but not in my case. Adding extra hose lengths would reduce the efficiency even further.
 

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Yeah I took it as something to use sporadically as backup or small room cooler.

In our case I just needed anything. There was literally nothing ... Portable or window unit in inventory just a few weeks back.

Save one window unit which was something like 110 pounds. Just didn't think I could install it. And since it was a temporary situation.. I skipped it.

Nice unit though, maybe claimed 1000 SQ ft or more.

Anyway thats not going to work for you.
 

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Discussion Starter #5
I'm surprised there was nothing in inventory in mid summer. I usually get appliances from a local place (not a big box store). That's where I got the 8000 BTU unit. I picked it up at their warehouse and they had loads of A/Cs there. They didn't have exactly what I needed a few years back (low profile A/C for a wide window). Since I didn't need it "today", I used Amazon and got free shipping.
 

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I don't know how much clear wall space you have between rooms (staging and train), but if you have room for additional Broan transfer fans, you might consider putting in a few more. When I left the HVAC commercial business a few years back the latest trend was to equip new havc equipment with "fan walls". These fans were high CFM and could generate high pressure and the Broans are certainly not capable of that. But, it stands to reason, if you can transfer more cool air into your train room from the staging area, the train room will become cooler. Heck, I would even try putting in a couple for reverse flow. In other words, blow some of the train room air back into the staging area. The idea here is to exchange as much air form one area to another and try to achieve a more balanced temperature between them. For what those Broan fans cost, it wouldn't be a big expense, and with a little ingenuity and time, you might come out with something much more livable for you and your trains. Good luck.
 

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Any solution should try to follow: Outflow up high, inflow down low.

In my other forum (loudspeaker/amplifiers) a guy had lots of electronics heating up his man-cave. The room didn't have AC but abutted his living room that had whole-house cooling. He had airflow from the living room via fan in the wall up high and was relying on the space under the door for to exhaust the inflow back to the living. He couldn't understand why cutting the bottom of the door shorter and shorter - to allow a bigger opening back to the living room - wasn't helping.

That's because he had the hot air up high flowing into his man-cave and the cold air down low flowing back to the living room.
 

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Heat rises, but also, heat flows towards cold. Understanding airflow and heat transfer helps in rectifying common problems with residential heating/cooling systems. Simply running the furnace fan or air handler 24 hours a day, and keeping all interior doors closed will help greatly to level out interior temperatures. Some may disagree, but it will work.
 

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You don't even have to run the fan 24/7, if you just configure the central heat to run the fan 10-15 minutes an hour, it makes a huge difference in leveling the temperatures. I've programmed my thermostat for 15 minutes each hour running the fan, that leveled the temperatures out quite well.
 

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Discussion Starter #11
Thanks for the input guys.

I attached a sketch to show the location of the window A/C as well as the supply (green) and return (red). Not perfect, but it’s plug and play and as I said before, it gives me more train time.

Bob – The common wall space between the train room and the staging area is pretty much what you see in the third shot above. To the right of the fan is a chimney and beyond that, the roof of the attic is too low. To add another Broan, would mean removal of train drawers and cutting a bigger opening in the staging area which would require removing the Snyder shelves…not happening. The opening for supply in the staging area wall is 6”X12” (pretty close to the area of the 10” Broan fan). The air returns through doors with a much larger area so I don’t think I need a fan for return air.

John – I have used a box fan at times to blow heated air to the attic in the winter to get things started before I turn on the electric heater. Yes, it has much higher air flow than the 10” fan, but I wanted something that would not be in the doorway and I didn’t see anything besides the Broan to fit in the 16” wide opening that I liked.

Mike – While A low supply with a high return would be ideal for A/C, in my case, I am just using the existing openings. I’m sure some of the hot air from the attic sneaks right back into the supply, but the existing setup does make the attic more comfy, so I’m not too concerned.

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Discussion Starter #13
Look into one of the mini-split A/C units. I am building my train room in the attic of our garage. It gets hotter than hell up there in summer and colder than the same place in winter. I am going to install one of these.

That’s very interesting Madman. Thanks for posting. I never knew they made the split units as a DIY project. We are neighbors by the way. I’m in Oreland.
 

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Cool. We've been here forty-six years. Maybe when we can socialize once again in comfort, we can get-together.
 

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I've been to see you John. I'm the guy who took all of the tubular track you were giving away.
 

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We may all be getting a bit forgetful. Comes with great age.
 
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