What Size Air Compressor?

[David2011]

It's time to replace my old air compressor. It's a horizontal Craftsman boasting 4 "Craftsman horsepower." There's not even an amperage rating on the motor and it's not possible for a 110v 20 amp circuit to make 4 hp so I'm guessing that the real HP number is well under 2 HP. The replacement needs to be a vertical model and has to run on 110V.

The compressor that catches my attention is the Kobalt "Quiet Tech" 26 gallon unit. Does anyone know anything about this or similar compressors? https://www.lowes.com/pd/Kobalt-QUIET-TECH-26-Gallon-Single-Stage-Portable-Electric-Vertical-Air-Compressor/1001014062

Last time I used the old one, purchased around 1995, it made odd noises and I'm really getting concerned that the tank is at the end of its life. I don't want to find out I was right "the hard way."

[Winger Ed.]

It depends on what you do with it, how hard & often you run it, and how long you want it to last.

Over the years, I've worn out and burned up a few of the smaller ones.
Air sanders, paint guns, and sand blasting takes a lot of air, and tends to over work the small-ish ones.
Now, I'm on what I hope to be the last one I'll need to buy.
It's a 8hp commercial compressor sitting on a 80 gal. vertical tank and weighs about 500 pounds.

Keeping their air intake filter clean and change the oil once a year does them a lot of good too.

[Froogal]

I bought an upright, 60 gallon unit probably 30 years ago. The tank is all steel and the compressor unit is cast iron. Still going strong.

Pay NO attention to the artificial horsepower ratings. Mine is advertised as being 6 horsepower. I knew that was a bunch of you know what when I bought it. It probably is closer one horsepower, maybe two.

What you need to know when shopping for a compressor is to know what the C.F.M requirement of ANY of your air powered tools is, and then buy a compressor that exceeds that requirement. Horsepower means nothing. It is only a marketing strategy. How much air (CFM) the compressor will deliver is ALL you need to know.

[Handloader109]

I bought a HF quiet unit about 2 odd years ago. I can hardly hear it. It is smaller than my old dewalt pancake unit that put out about 120 dB. You couldn't even stay in the same room with that ***. This one is quieter than my 16g Brad gun. They along with others offer some larger units that are decently quiet and work well

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[Mk42gunner]

Tank size and C.F.M. seem to me to be the governing items for a home use air compressor. As noted the HP ratings are a joke.

If you have trouble running your air tools, try to find a bigger hose, more volume available does wonders.

Robert

[M-Tecs]

I don't know about the current oil-free compressors but the older ones are anything but quiet.

https://aircompressorsusa.com/oil-free-air-compressor-vs-oil/#:~:text=Noise%3A%20One%20of%20the%20biggest%20dif ferences%20between%20the,level%20might%20be%20an%2 0important%20factor%20to%20consider.

I have single stage two-cylinder C-Aire that was purchased to replace a "quiet" oil-free piece of junk. The C-Aire to very very quiet.

[ulav8r]

Replaced the oil in my 2 horse unit yesterday. I think it was due after 30 some odd years. It was purchased at Montgomery Wards and is an honest 2 horsepower.

It is small for some uses. The wife has purchased a small sandblasting cabinet that will require a much bigger compressor.

[BLAHUT]

I bought a twin tank and an upright from harbor freight years ago for construction work. the twin for floor nailing and trim work. figured if they wore out in a few years not a big loss with the price at the time. both run on 110 v. both are still going strong. all depends on what you want to use them for? I have a commercial 5 hp with a 20 Gallion tank that runs on 220v don't even plug it in any more, the other two handle all I need.. and are quieter.

[xs11jack]

Some one got promoted by measuring the start current of the motor on the compressors they were making. The few parts of a second that the motor draws is really high compared to the running current. Most compressor that are made to be run on 120 volts will only draw 15 amps because that is the standard house current. Oh yea, you won't find the running current rating anywhere on the spec. plate on the compressor or anyplace.
Ole Jack

[pworley1]

Get the biggest one your circuit will carry.

[Mal Paso]

Replaced the oil in my 2 horse unit yesterday. I think it was due after 30 some odd years. It was purchased at Montgomery Wards and is an honest 2 horsepower.

It is small for some uses. The wife has purchased a small sandblasting cabinet that will require a much bigger compressor.

If it's like my "Craftsman", it's an honest 2 HP pulling 11 amps X 240 running and was actually made by Speedaire.

I use Milwaukee electric wrenches now, the big one is 1,400 foot pounds, more powerful than my 1/2" air wrench. I downsized to a Makita 1.5HP portable for tires and cleaning parts.

[David2011]

Some one got promoted by measuring the start current of the motor on the compressors they were making. The few parts of a second that the motor draws is really high compared to the running current. Most compressor that are made to be run on 120 volts will only draw 15 amps because that is the standard house current. Oh yea, you won't find the running current rating anywhere on the spec. plate on the compressor or anyplace.
Ole Jack

Yeah, I knew where the horsepower ratings came from. What I don't know is how many microseconds it has to drain that much power but it's definitely shorter than the trip time of an average household breaker. Four HP at 115 volts is about 26 amps. That much 115VAC power is usually only available at marinas and RV parks.

[David2011]

Guess I should have posted the long version. I regularly post too many words. Can't help it. I take after my maternal grandfather who never met a stranger.

More details: Anything that is not semi-portable and requires more than 110/120VAC is too big. The "4 HP," 25 gallon compressor I currently have has been 100% adequate for the past 27 years. If I had a 4000 square foot shop a big cast iron compressor with an 80 gallon tank would still be way too big. I know how to calculate loads based on the air tools I have but I just don't use them to the point of outrunning the compressor I've had. All day capacity isn't significant since all air tool usage is brief. The biggest projects I anticipate at this time would be painting my large scale R/C airplanes. That would be about the same as painting the front clip of a modern car and would be done with a touchup gun because the largest parts are wing panels no more than 20"x60" each.

[Moleman-]

If you're going to use it much don't get an oilless pump. They don't last as long as a standard compressor.

[David2011]

I'll keep that in mind. The current oilless pump has only lasted 27 years.

[Shopdog]

Not counting the large shop 2stage compressor;

Over the years in the building biz,have DESTROYED 1/2 dz + compressor. The twin tank/KV head Emglo knockoffs are pretty durn good. I got a DeWalt labeled version that has been completely adequate. Sprayed 2 kitchens(lacquer/cabinets) with it,on site. It is all this style "wants". Yes,we have all the right HVLP "stuff". Be forewarned,these twin tanks are freakin heavy. But,is the minimum for nail guns and paint guns.

Next up is those 30g vertical style. These are what most of the roofers around here use. They beat on them,HARD for a cpl years and then snag another. We had an "early" version of a Cman 30,20+ years ago,will run two framing guns. That poor thing stayed on the back of my pickup,rain/shine for almost 5 years. Early oiless. Deafening loud but otherwise bullet proof. Sorta rebuilt it and gave it to #3 son. Put out to pasture so to speak. It is a horizontal.... this was before most co's went vertical on this size.

I'd find a vert 30(28,whatever) with the Emglo/KV style head. The green,Hitachi 50' hoses sold at homeboy stores are what most roofers use..... seen these hoses live through absolutely disgusting conditions and keep on banging away. Good luck with your project.

[Shopdog]

One more tidbit on smallish comp.

Two scenarios,illustrating do's and don'ts. Think of a roofer with a nail gun. He's "above" the tank...well above. The moisture being CONSTANTLY produced by this sized outfit is STAYING at the comp. Yes,drain every few hrs.

Second scenario,or "don't"....

Comp. is on the truck,but we're down in a basement framing or shooting cabmets. Here the gun is WELL below the comp. Wonder where all the moisture ends up? Yup,right at the gun. You drain the tank and it's like,"cool we're having a great day" because there's nothing coming out the drain. Looking at your guns innards,you'll know where it all is.

Gravity plays a HUGE role in where the moisture ends up.... so stack the deck,and use this to your advantage.

[Scrounge]

If you're going to use it much don't get an oilless pump. They don't last as long as a standard compressor.

I'm another who wouldn't bet on that. Mine is a Campbell Hausfield 20g tank, and I've had it 23 or 24 years. I know it will die one of these days. Maybe even today. But I bought it to fix my 77 Plymouth Volare when it welded a bearing on the front right axel. It was going to cost about $1K to have it fixed, or I could buy the parts and tools, including the air compressor and air tools for about $800. Wife asked if I'd still be able to use it after the car was fixed. When I said yes, she said get it. When it starts up in my shop, which is the former back porch, it scares her to this day, but she's happy to to have compressed air whenever we need it.

[GregLaROCHE]

I have a small compressor that works for filling tires and spray painting, but I’m dreaming of one that could power my air tools that have been put I storage for twenty years. I have seen some setups with up to four compressors on top of a volume tank. For some reason I don’t want to trust them.
I have a three phase 4hp motor that I have thought of using. However, the cost cost of the compressor is not that much, but when you add the volume tank, regulators and fittings, the price gets up there. Plus there’s all the work to do to put it together. I’m wondering if I shouldn’t just buy a cheap Chinese one and expect to throw it away in a few years.

[johnsonian09]

My father purchased a 60gal husky (or craftsman..?) compressor from HD probably when I was around 8 years old. Still works, despite both his and my antics. It’s on wheels, I repainted my wife’s c30 with it several years ago..

I think no matter what brand you buy the larger motors are more reliable.

Hell I bought that baby Ryobi 1 gallon battery powered 18v/4 amp bat to run some 18 gauge nail guns at customer houses. Shoved it inside an old stackable husky box lined with insulation and plumbed the hose thru it. You couldn’t hear the thing running in the box. And that works great years later despite the name of, and color of it.

Any of the Big box store 30gal+ will take tires off a car and paint small projects, run nailers etc. And if you decide you need more capacity to run tools longer you can open up the regulator, attach a extra inline tank, then regulate that tank down to your tool pressure and you’ll trip the motor less.

I know roofers who just run a pancake compressor and a tank. I think they are about 15- 20 gallons but I’m not sure.

If this is for yourself and not for a production crew, does waiting an extra 30seconds for the thing to run pressure back up really matter?

If this lives in your garage and not in the truck bed:

The advantage of the bigger ones, is that they are usually worth fixing. And there’s someone local you can pay to have it done if you don’t want to DIY.

The advantage of the small ones, is if it breaks 5 years in, you’ve typically already made that money back out of it and you can just replace it if fixing it is out of your league or just don’t want to.

I haven’t heard of anyone local using kobalt tools. Looks like it would last several years and the reviews aren’t bad. And I don’t think you’ll regret getting that one.

I had a dewalt that looks similar and approximately that size, first day ripped the drain valve right off the bottom when transitioning from uneven asphalt to a wheel chair ramp. Blew the valve to god knows where. So if your valve is in dead center on the bottom of your tank, depending on how much it juts out you may want to spend the 20$ on a valve relocation kit with a short and tight 90 elbow , which also just makes it easier to operate slightly and less likely to forget you need to Drain the thing if you can see the valve.

Run a small tube into a old milk jug to catch water and empty it when it gets half full. Doesn’t cost any time to drain the water out when your done, and your tools will thank you for it in longevity.


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[Moleman-]

I'll keep that in mind. The current oilless pump has only lasted 27 years.

Like I said "if you use it much". The last 30gal oilless one I had burned through two pumps in 8 years. Put a 3rd one on and replaced it with a 220v 60 gallon oil filled pump 10 years ago. No issues.

[lightman]

The timing on this thread is great for me. I'm looking at compressors again. We recently moved and I miss my shop! I had a 5hp 2 stage 80 gallon vertical compressor that would run anything that I had but I didn't have room for it at our new house. I fear the anything that I get after owning that one will be a letdown.

[GregLaROCHE]

Most new tools and equipment are let downs from the old made in USA stuff!

[farmer66]

I have a slightly different opinion. I run a Craftsman 1997 5 HP 30 gallon compressor on 115 V. Nameplate says 15 amps, so that amounts to only 2.34 electrical power. So they put a 5 HP motor on a 2.34 HP compressor, maybe that is why it runs so well. I like the short run time to get decent pressure. I replaced cylinder and piston last year. It is oilless, cost $26 and took 30 minutes. This does not run continously, but several hours most days.

So I suggest going to the yard sales and seeing if you can snag on older model.

[jonp]

I bought a HF quiet unit about 2 odd years ago. I can hardly hear it. It is smaller than my old dewalt pancake unit that put out about 120 dB. You couldn't even stay in the same room with that ***. This one is quieter than my 16g Brad gun. They along with others offer some larger units that are decently quiet and work well

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Second on the HF. Got a larger high compression one supposed to be as good as one twice the size and quieter. It certainly is.

[ebb]

My old boss put a Keaser in my shop. I told him to get a cheaper piston type. That the scroll type was not worth the money. BOY was I wrong. Quiet and lots of air super dependable.

[Mal Paso]

My old boss put a Keaser in my shop. I told him to get a cheaper piston type. That the scroll type was not worth the money. BOY was I wrong. Quiet and lots of air super dependable.

A friend has a Fujitsu Air Screw on his drill rig. Powers it with a 12 cylinder Allison aircraft engine. It puts out 350 CFM at 300 PSI. Not Quiet! I worked next to him one day, that was enough.

[MaryB]

I bought a 60 gallon Northstar compressor form Northern Tool, 11.5cfm @90psi, 240 volts/15 amps 3.7hp motor. I check oil once a month, drain it weekly because I use air tools pretty often. When I ran air lines I ran one into the house in the pantry, buried in conduit from garage to the house. Now when I do any home repairs I can run an air nailer or a sander in the house, I just run a hose into the pantry which is bottom floor center rear so centralized. 100' of hose gets me everywhere with plenty of slack.

I do need to add a dryer for painting. I restore old radios and the metal cabinets get sand blasted if they are rusted then pits filled with a skim layer of body putty, sanded smooth then painted in a matching paint for that radio brand. Also do some cabinet restorations for other ham radio operators who do their own electrical restoration. Right now I have stuck to painting in cooler/drier weather, summer I get to much moisture in the air lines to spray paint with a touch up gun.

Friends have painted some cars in there too by hanging plastic from the ceiling to make a paint booth. Lay plastic on the floor too to not only protect it but to stop dust.

I bought mine on sale for half this price, YIKES stuff has gone up! https://www.northerntool.com/shop/tools/product_200756209_200756209

[redneck1]

A few years ago I needed a new air compressor and didn't have much money to spend so I got a 20 something gallon harbor freight special for $139 after my coupon I think it's 4 cfm or there about .

I used that thing hard running mist coolant for 2 solid years .
The only complaint I had with it is that it loud , drive you insane loud .
Only reason I replaced it before it quit was I just couldn't take the noise any more.

[David2011]

A friend has a Fujitsu Air Screw on his drill rig. Powers it with a 12 cylinder Allison aircraft engine. It puts out 350 CFM at 300 PSI. Not Quiet! I worked next to him one day, that was enough.

While I love the sound of 12 cylinder aircraft engines (partial to the Merlin) that would be a bit much.


A few years ago I needed a new air compressor and didn't have much money to spend so I got a 20 something gallon harbor freight special for $139 after my coupon I think it's 4 cfm or there about .

I used that thing hard running mist coolant for 2 solid years .
The only complaint I had with it is that it loud , drive you insane loud .
Only reason I replaced it before it quit was I just couldn't take the noise any more.

I know what you mean. The one I’m replacing is loud, too. It is running at somewhere between 3450-3600 rpm and beside being loud it’s an annoying sound.

[rbuck351]

HP is rated different than it used to be. Running amp/hp was the early way of rating hp. Now hp is rated on starting amps which is usually over double the amps of running amp draw.

[poppy42]

Tank size and C.F.M. seem to me to be the governing items for a home use air compressor. As noted the HP ratings are a joke.

If you have trouble running your air tools, try to find a bigger hose, more volume available does wonders.

Robert
Ah not exactly true but kinda. If your Compressor puts out X number of CFM doesn’t matter how big the hose is leading to your air tool it’s still only delivering X number of CFM! However if the size of the air hose is not allowing the maximum number of CFM supplied by your compressor to reach your air tool because the diameter of the air hose is so small then yes getting a bigger hose can help.

[Mal Paso]

If you can find one with an 1800 RPM motor it will run cooler and water vapor is less of a problem. Most are 3600 and use a compressor half the size. Larger compressor dissipates heat better too. 1800 is quieter too.

[farmbif]

ive got and had a bunch of em over the years. Ingersoll rand are very good, reliable last a long, long time if maintained and parts are always available if something gets broken or wears out.
but the big question is what are you wanting to use it for. and do you need 135psi or 175 psi/ single stage or double stage if its a reciprocating piston compressor. do you plan to run it every day or just every now and then? do you want a cast iron pump that will last many years of daily use or aluminum pump that won't last nearly as long
some of the smaller cheaper ones use a diaphragm to compress the air, these dont usually last very long.
I forget the formula but it is something like 4cfm per horsepower with 1800 rpm electric motor, 3600 rpm motors only produce 1/2 as much torque of an 1800 rpm motor. if memory serves me right.

[abunaitoo]

Oil free compressors are noisy.
If you want quiet, check out a screw compressor.
They are kind of expensive though.
I have an old Craftsman 5hp that I got new in the 70's.
I found a 80gal tank, and mounted it on it.
Planing to change again to a 60 gal tank.
Compressor broke a reed valve once.
Easy to repair.
CFM is everything.
With all the chinese junk around, HP means nothing these days.
Even the CFM is suspect if made in china.
Mines was made in the good old USA, when Craftsman was great.

[David2011]

Unexpected followup: I still hadn't gotten around to buying an air compressor. I had to allow for all the setup time as well. Fast forward, the next door neighbor was having a pool party. I asked him how he liked his compressor, an older upright belt driven Chinese "Magnum Pro" with a 35 gallon tank. Silly horsepower rating is 5HP. I haven't checked the motor to see if it has an ampe He said that it came with the house. He fired it up when he bought the house to see that it ran but never used it. I asked if he wanted to sell it. He said that he thought he had told me once before that I could have it. Could I have forgotten such a generous offer? Anyway, we moved it from his house to mine a couple of days later.

The fantasy horsepower rating is 5HP. I haven't checked the motor to see if it has an amperage spec on it yet. I changed some fittings and gave it a pressure test which it passed. There was a slight pressure drop over 2 hours, on the order of 3 to 4 psi. That could easily be the drop in temperature from freshly filled to sitting for 2 hours. It's in a store room in the garage with no direct access to the workshop and a solid insulated wall between so it can just barely be heard in the shop. With the TV on you can't tell the compressor is running. When the shop was built I had a circuit put in just for the compressor. It has an indicator light on the shop ceiling which has a blue bulb in it to remind me that the compressor circuit is live. I've ordered a thermal magnet breaker for that circuit that can be used as a switching breaker. It will probably last as long as I do. I'm making it very easy to drain the water frequently.


Here's a photo of one that I snagged from the Internet.

316587

[Winger Ed.]

Looks like it'll do a good job for ya.
Change the oil in the pump every year or so and they'll just about live forever.

[abunaitoo]

Looks like a nice size.

[Tall]

The air compressor needs to have enough output (CFM rating) to easily exceed the biggest tool you plan on running so that it does not run all the time and you don't have to wait to let it "catch up".

I bead blast often so I bought a big Ingersol Rand. It's rated at 21.5 amps on a 250 volt circuit. It keeps up with my needs easily. Should be the last one I ever have to buy.
316611

https://www.bing.com/shop/productpage?q=ingersol+rand+air+compressors&filters=scenario%3a%2217%22+gType%3a%2212%22+gId%3 a%22151983356449%22+gIdHash%3a%220%22+gGlobalOffer Ids%3a%22151983356449%22+AucContextGuid%3a%220%22+ GroupEntityId%3a%22151983356449%22+NonSponsoredOff er%3a%22True%22&productpage=true&FORM=SHPPDP&browse=true#br-description

[Rapier]

Compressor oil and an oil change right off.....with a good cleaning on its outside. I keep a diaper under mine to catch the water and any oil by pass. Reason to put filters on your outlets if you want to spray coat. Most of the coatings do not like water or oil.[smilie=s:

I have a 90 bolted to the flor and hard piped around the shop. Drew it into the shop plans. But a free compressor is a good thing, it it works OK.

[David2011]

I bought oil already. Still working on the “permanent” installation; should have all the parts in later today. I’m going with Milton Highflow V fittings simply because I like the way the collar retracts and reconnecting is easy. I’m done with the leaky imported couplers.

Tall, thanks for the contribution but there’s no way I could justify a compressor of that size.

My last compressor was adequate for everything I asked of it. This one has a tank almost twice as big and the CFM ratings are much higher. I’m not using it commercially so if I have to wait for it occasionally that’s OK. Most- not all, but most of my air needs can be satisfied with a 2 gallon portable. I use it for clearing chips, driving brads and light shop duty far more than running air tools, painting, blasting, sanding and the like.