Am I an idiot for just leaving my acoustic guitar out of its case?

I’ve a very nice Martin D18 thing, and I really just want to have it left out (ideally on a hanger) in the house. 

I keep mine out and don't worry about it. I think it's mostly a problem if you're somewhere with extreme temperature and humidity variations like parts of the US. 

I keep 2 of mine out at all times, just about. We have no radiators but central AC and humidity moving between 50-70% typically. Occasional truss rod tweaks needed but nothing else. And in reality the thinner-necked electrics are the only ones that need that

In the UK, you’ll be absolutely fine. However, do avoid leaving it out right next to a radiator. That could cause harm. Other than that, it’ll be fine.

Hanging on a wall that is external to the house is also bad, I think it's do with relative temperature of the front and back of the guitar (an external wall is colder).

Guitar shops do it all the time

Guitars kept in cases don’t get played

Mine's kept in its case when not in use but I do use it alot! The room its stored in is a mostly stable temperature so not too worried.

thermionic said:

Hanging on a wall that is external to the house is also bad, I think it's do with relative temperature of the front and back of the guitar (an external wall is colder).

If I'd hung a guitar on the wall of some places I've lived it would have got so damp that mushrooms could grow inside!

sweepy said:

Guitars kept in cases don’t get played

Very true. My cheapie that I play all the time is left out in a rack. My 2 expensive ones are in cases under the bed in the spare room. I never play them but open the cases and look at them once a year ish.

I have two acoustic guitars and a mandolin on hangers, I do have a little digital hygrometer in the room just to be sure, it's quite a dim, shady room and they're not above radiators. It's probably a touch more risky compared to storing in cases, but I play them so much more when I can just grab them while the dog is napping. If I faff around getting cases out he might wake up and want attention.

All fantastic advice. Internal wall, away from radiator. Play the thing. 

They sound better when they're left out on a stand or a wall hanger so the strings can continuously resonate with all the noises in the room.

That's not a joke.

ICBM said:

They sound better when they're left out on a stand or a wall hanger so the strings can continuously resonate with all the noises in the room.

That's not a joke.

I have often had the experience of a guitar “jumping” about on my lap in resonance when i’m sat down listening to something on the stereo, so I don’t doubt this claim.

My CS Martin is always on the wall.

My Lowden was only in the case to come to my house, otherwise I think it's been in it once. 

More than 30yrs of leaving guitars out or on wall hangers in UK. Zero issues.

Yes. You are an idiot if you leave it out of its case without measuring humidity. Temperature you can guess, but humidity is more difficult. Just buy a hygrometer - a really good one will cost about 1% of what you paid for the Martin. Then you will KNOW you are safe, and also know if you need to pop it into its case at certain times. 

Don't guess. Don't wonder. Don't ask here. Don't worry. Don't hope. Measure. 

thisisguitar said:

My Lowden was only in the case to come to my house, otherwise I think it's been in it once. 

Ditto

Does the case in itself protect against humidity? Especially if you are going to open and close it to play the guitar?

SlopeSoarer said:

Does the case in itself protect against humidity? Especially if you are going to open and close it to play the guitar?

It will protect against sudden changes in humidity as, when closed, it will take longer for the inside of the case to be the same as the humidity outside it. But unless it’s properly sealed - like Tupperware who, as far as I know have never branched into musical instrument cases :) , the case will eventually reach the same humidity as its surroundings. 

Adding to @drofluf's excellent answer, the case will also protect against multiple short-term changes of temperature and/or humidity. Suppose that you live in a warm climate and turn the air-con on when you get home from work each day to cool the place down. (This will almost certainly change the humidity too, sometimes dramatically.)  In a case, the guitar will see little of this daily fluctuation and be just fine. Outside the case, different story. Or consider the reverse - cold cliate and a heating system. Same deal. 

Hammering away at the same point yet again, only by measuring can you find out what is really going on, and (if necessary) take action.

Tannin said:

Hammering away at the same point yet again, only by measuring can you find out what is really going on, and (if necessary) take action.

I’ve got a couple of these https://amzn.eu/d/60Icl8E humidity meters. 

The foam padding (and soft fluffy material) that lines a guitar case is effectively a sponge that can hold a lot of moisture. If your house has a generally high relative humidity level I think it’s a good idea to try and dry the inside of a case every so often. I sometimes lean one open next to a radiator, or give it five minutes with a hairdryer on a low to medium heat.

If a guitar is out of its case then you are more likely to grab it to play. I've had guitars costing much more than your Martin hanging out in the open (via Hercules long-arm hangers) for years without an issue. It is wise to buy one of the many cheap humidity monitors to check your chosen location is safe - and don't do anything silly like putting a guitar near a radiator or exposed to direct sunlight.

The only issue I've had was with a custom Shapelywood travel guitar after leaving it in the loft (IN ITS CASE) for a few years.

Thanks @drofluf and @Tannin. I've ordered a couple of those humidity meters too.

thermionic said:

The foam padding (and soft fluffy material) that lines a guitar case is effectively a sponge that can hold a lot of moisture. If your house has a generally high relative humidity level I think it’s a good idea to try and dry the inside of a case every so often. I sometimes lean one open next to a radiator, or give it five minutes with a hairdryer on a low to medium heat.

Absolutely.
Also, don't piss in the case when catastrophically drunk (my friend suggests).

I absolutely hate hanging guitars on a wall for some reason or good reason. Dust will get in it with an electric and the pots don't like that. I have cases for all of mine and that's where you'll find them.  It"s very true that a guitar in a case is less likely to be played though. I leave at least one acoustic and one electric of the day out on stands to grab when I feel like it. The other problem with having too many guitars is that you don't spend enough time on the one instrument to properly bond with it or master it. For this reason supposed to be selling a few in the last year and I have sold 3. Managed a year with no new guitar purchase until the other day and failed 2 days later. 

I don't have a case.

I am one, but don't have one.