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Discussion Starter #1
I'm planning to build an 18' x 26' garage this Spring for minimumal part time auto body repair work. I long ago reached the age of maturity and was owner of my own professional shop in the 80's. My goal is do spot repairs not overall paint jobs. I'm fully aware of the safety and health concerns of the trade and will implement the necessary safeguards throughout. The garage will have 2 x 6 construction with 10'x 5/8" gypsum fire rated walls, 1 steel man door and 8' x 10' steel main door. Everything will be insulated to the max from the slab up. MY QUESTION; Will a Ductless Heat Pump (with heat strip) satisfactorily heat this building throughout the Winter in a cold N/E climate? It is fully understood that all sources of ignition will be located in a separate room behind a steel door with room vented. Switches, lights, motors will be explosion proof and/or sealed from ambient contaminents. With exhaust ventilation running, proposed heat pump wall unit would be turned off (if possible) and covered before any combustible solvents are used. I do not care for oil, kerosene, propane, natural gas or wood as a heating source. That only leaves a Heat Pump or construction type heaters. I appreciate your input and recommendations. Thank You
 

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Ductless/mini split heat pumps, stop providing heat between 14 and 0°F.
So you would need a second source of heat, if your area drops to those temps.
 

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Been There; Appreciate your response. Yes in January and February it can and does get much colder than that. I wondered if the advertised built in "Heat Strip" would provide enough warmth on an "as needed" basis. Of course, at a much higher operational cost!!!! Is it best to choose units with the highest SEER rating in order to get best overall efficiency/lowest cost operating use?
 

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Higher SEER will help with cooling cost.

As far as I know, only a few of the low SEER units have an electric heater also.
Higher SEER units don't(inverter models).

So if you get a Lower SEER with a built in electric heater.
Then you may not have to put in another additional source. Depends on how big the heater is.
 

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This is not dead on the question, but I wanted to relate a ductless experience I had a few years ago that will sound unbelievable.

I had a 3000 sq ft building (50x60) built with 16 ft ceiling. It had two 10x14 metal insulated doors, and a commercial glass door (all doors faced north). the building was insulated to the MAX.

We installed a 115,000 btu Modine unit heater for heat (this is not an option for you) and it was fine. The thing that blew me away was the cooling. Being in the lower midwest, I knew better, but my boss at the time (400 miles north) insisted that we would not need AC:huh: It gets to 100 here in the summer.

Anyway, we had an open warehouse with an open office in the middle of the room (imagine super fancy lemonade stand). When he came down in the summer, he almost died from the heat and so we installed a 2 ton Ductless Heat Pump on the back wall of the office to basically cool the guys we had working in the office area. What actually happened is that this unit cooled the entire building very well.
2 ton + 3000 sq ft + 16 ft ceiling = :rockon: (who woulda think?)

The moral of the story is that your insulation efforts will pay big dividends.

Since heat is your main issue, and you indicate that you will have a seperate room for things that ignite, you might want to consider a Standard Split heat pump with an air handler with strip heat located in the "safe" room. Then you could run a single trunk and discharge evenly.

I think you are going to be hard pressed to find the back up Heat Strip.

Another alternative is a PTHP (motel unit with the max 5kw back up resistance heat.) Much easier install and cost.

Good Luck

Jay
 

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I would imagine it would be VERY difficult to isolate the indoor unit from any fumes which will eat the copper etc. Would need an airtight box. As much as you don't like gas a small Reznor airtight heater may be the best bet. The indoor unit of a minisplit system has a lot of plastic in it and is designed to be kept at around 50 degF. If it ever gets colder in the garage/accidentally it may split and get damaged.
 

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Discussion Starter #7
Home Air Direct..........I had not even considered the PTHP you've suggested. Seen them, yet know nothing of their versatility or more importantly, the cost. I would have thought they would cost more than a split unit where there is an outdoor unit and a wall mounted unit. Since they've been around forever, I can imagine it would be possible to pick up a used set. Again, what would a new setup cost and should I stay away from all HVAC equipment "used"? Some of the split units I've seen advertised show a heat strip. Venturing into unknown territory here!

Yuri: Televised neewscasts of homes blown into a billion pieces scare me from using natural gas anywhere on my property. I believe I could isolate the indoor unit inside a wall mounted metal box for protection from vapors using the unit only when no spray is present. Back years ago in my shop which painted numerous cars weekly we had exposed copper lines for air, even a large wood furnace for heat. We always took precautions with ventilation yet there was no apparent damage to copper or plastic fixtures. You know a lot more than me about this subject. Placing equipment like this in a garage environment may even void the warranty. Consider also that it will not be used consistently, 40 hrs. weekly, rather part time, as needed.
 

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What kind of exhaust system are you installing for the spray booth.
 

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Gas is very safe and the only explosions are caused by unqualified people trying to service units and/or gross negligence on the part of the installer. Minisplits are expensive $4,000 and up. You may not have warranty as they are intended for residential use and not necessarily dusty garages. I have worked in autobody shops and it is impossible to keep all the dust out of equipment. Body filler dust is like drywall dust and impossible to get rid of all of it. If it gets into the fancy plastic blower wheels and bearings of the indoor unit they won't last long. They do not have a fine filter for that kind of dust. Get a airtight Reznor and a propane tank would be my suggestion.
 

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Discussion Starter #10
Been There: Originally planned using a Tube Axial Fan then changed plan to use something like a "Jenny" fan for exhaust, even one from Princess Auto; both are explosion proof. Exhaust and Heating have been major headaches for me and still undecided. I had designed a plenum for the fan yet some local ventilation "experts" say I don't need a plenum.

Yuri: I can appreciate what you are telling me. A year ago I quickly ruined three (new) grinders using abrasive cutoff wheels to cut through brick. The bearings and motors could not tolerate the fine dust! I imagine the propane & Reznor setup could get expensive but may be the best alternative.

Wish I could show you both the garage layouts and draw from your recommendations on intake and exhaust air requirements. I've tried twice to attach the garage plan I made with Google Sketchup but keep getting message "your submission could not be proessed because a security token was missing." Would you both let me know if I could email you my proposed layout plan. Thank You Kindly.
 

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PM me, and I'll give you my email address.
 

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"Princess Auto"? you must be close to where I live (Manitoba company). I am not good at designing ventilation systems so don't bother with the layout plans.

Good Luck:yes:
 

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Sent another one to you.

As long as you get the email, you can just use reply, and send your layout to me.
 

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Discussion Starter #16
Ductless Heat Pump for Garage

Sorry for delay in responding. Had considerable trouble sending Garage Plans. 5 in all. Please go to this link......
http://s679.photobucket.com/albums/vv158/brittlediabetic/


My biggest concerns are Heat Source as heat will be sucked out with the exhaust fan in cold weather. I had originally wanted to incorporate an electric or propane construction heater behind a bank of intake filters to warm incoming air from outside vent. It would have to be used only after vapors have been removed from garage. As well, it is important to be able to close (insulated) vent to outside when not in use to stop heat loss and cold air from coming inside. The same concern is for the exhaust fan at the back of garage and how to insulate the ducted vent when fan is not in use????

Beenthere, (OR ANYONE) can you provide any insights to my dilemma?
All assistance is greatly appreciated. Thank YOU.

brittlediabetic
 

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Whats the CFM of the exhaust fan?
 

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Discussion Starter #19
Ductless Heat Pump for Garage

About 3,500 CFM. This is another area of controversy. Pro spray booths of similar size as garage area use tube axial fans of 10 - 12 thousand CFM. A U.S. fan supplier who purports to have decades of spray booth experience says 3,000 is adequate for this room.
 

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It probably is.

At 3500CFM.
In order to maintain an indoor temp difference of:
Temp---BTU
----70------264600
----60------226800
----50------189000
----40------151200
----30------113400
----20------75600
----10------37800

Those are the numbers if the exhaust is going to be running for more then a few minutes(5).

After that, the building and its contects will start dropping in temp quickly.

So what indoor temp do you want to maintain while painting. And how long do you expext to run the exhaust at any one time.
 
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