Do I Really Need To Use The Back Grill of My A/C?
July 18, 2020 12:37 PM Subscribe
I just bought a new Frigidaire air conditioner, model FFTA103WA1. It is through the wall, not window, but we put it in a window -- without the back grill.
The reason we got a through the wall a/c and not a window a/c is because we have bars on the window, and, therefore, we cannot use a window a/c because it couldn't be pushed far enough out the window for the side grills to be outside. (A through the wall unit is solid on the sides and just has intake through the grill on the back). This is the second through the wall a/c we've had in this window. The first one just broke, after more than 20 years.
This a/c, like all through the wall a/c units, comes with a back grill. The manual says we need to install this back grill because it's a “dual intake” grill and the feature that makes the unit so great (I had no idea of this when I ordered the unit). But we have NOT installed the back grill, because it's in a bunch of parts and we can't fathom drilling four holes in the air conditioner for various reasons and the a/c is already sticking into the room too much and the grill will add another inch or so to the depth of the unit.
Now, we did NOT use the grill on the first a/c we had in this window, and this never presented a problem. You just saw the guts of the a/c when you looked at it from the back, but, since this a/c is in a first floor back window, we didn't care how it looked, and, as I said, it worked fine for over 20 years. And now, the actual question:
Is it okay to leave out the grill on this a/c even though the manual says everything in our lives will fall apart in a million ways if we don't install it?? (or, at least, the a/c will not work correctly.) (It's on now, for the first time, and it's great so far). Is this true? What will be bad about the way this a/c works if it doesn't have a grill?
The reason we got a through the wall a/c and not a window a/c is because we have bars on the window, and, therefore, we cannot use a window a/c because it couldn't be pushed far enough out the window for the side grills to be outside. (A through the wall unit is solid on the sides and just has intake through the grill on the back). This is the second through the wall a/c we've had in this window. The first one just broke, after more than 20 years.
This a/c, like all through the wall a/c units, comes with a back grill. The manual says we need to install this back grill because it's a “dual intake” grill and the feature that makes the unit so great (I had no idea of this when I ordered the unit). But we have NOT installed the back grill, because it's in a bunch of parts and we can't fathom drilling four holes in the air conditioner for various reasons and the a/c is already sticking into the room too much and the grill will add another inch or so to the depth of the unit.
Now, we did NOT use the grill on the first a/c we had in this window, and this never presented a problem. You just saw the guts of the a/c when you looked at it from the back, but, since this a/c is in a first floor back window, we didn't care how it looked, and, as I said, it worked fine for over 20 years. And now, the actual question:
Is it okay to leave out the grill on this a/c even though the manual says everything in our lives will fall apart in a million ways if we don't install it?? (or, at least, the a/c will not work correctly.) (It's on now, for the first time, and it's great so far). Is this true? What will be bad about the way this a/c works if it doesn't have a grill?
Taking a gander at a random Frigidaire installation manual it is pretty obvious what the purpose of the dual intake grill is.
To operate, the unit is going to need to suck in ambient-temperature air (cooler) and exhaust out the air after it has passed through the coils (hotter).
In the dual intake system it sucks in the cooler air from the sides (two intakes, right and left, thus the name "dual intake") and blows the hot air out the middle.
So, the hot air (exhaust) is actually quite a bit hotter than the ambient air (intake). Something like 30-40 degrees (fahrenheit) hotter.
The difference between these two temperatures is what makes the a/c unit work. If the difference between those two temperatures is only 10 degrees, help! This unit can barely work at all! It's barely cooling and internally, it's working its head off and everything is getting all heated up to accomplish not much of anything at all.
On the other hand, if the intake/output difference is say 40 degrees, then it is real happy and works well.
What you want to do is take in normal ambient temperature outside air into the intake--that is air that is as cool as possible and maximizes the difference between intake and output air temperature that we were just talking about.
What you DO NOT want to do is re-suck in the hot exhaust air that is 30-40 degrees hotter than the ordinary ambient-temperature air. It's not only 30-40 degrees hotter than ambient air, even more important it is exactly the same temperature as the output air.
The a/c unit needs a difference in temperature to operate, and if there is no difference, it can't work effectively. Smaller difference than it needs, and effectiveness goes down a lot.
So the dual-intake system is designed to do exactly that: maximize the coolness of air it is intaking, and reduce the possible amount of hot output that goes towards the intakes. It sucks in the cooler air from an 'angle' off the the right & left side while channeling the hot exhaust air to move at a good clip right out from the center of the unit.
Undoubtedly there will be some mixing and some of the hot exhaust air will eventually make it back into the intake ports. But by the time it has done so there will have been a lot of nice mixing with regular ambient-temperature outside air and so no great harm done.
Whereas if you just remove the whole louvre system the hot exhaust air is just going to go out the back and then be sucked right back in the intake area, with only a little mixing with ambient-termperature outside air before it goes back in the intake.
So that is a long explanation, but the upshot is, to some degree the dual-intake vent panel will definitely ensure that cooler air is being sucked into the a/c's air intakes, which will make the unit operate a lot better.
"Operate a lot better" translates to: Cools the room a lot more effectively, uses less power/electricity while doing so, better avoids overheating and damaging the unit.
So it will do all that to some degree.
What is hard to say without doing some real testing, is exactly how important that is.
Like it might cool a little better, save a little electricity, and last a little longer if you have the dual exhaust vent in place.
Or it might work a lot better, save a lot of electricity, and last a of longer if you have the dual exhaust vent in place.
Guessing, it is probably not a little or a lot, but in between--a moderate savings, moderately work better, moderately last longer.
Maybe there is an a/c technician with actual experience who can weigh in.
posted by flug at 1:12 PM on July 18, 2020 [8 favorites]
To operate, the unit is going to need to suck in ambient-temperature air (cooler) and exhaust out the air after it has passed through the coils (hotter).
In the dual intake system it sucks in the cooler air from the sides (two intakes, right and left, thus the name "dual intake") and blows the hot air out the middle.
So, the hot air (exhaust) is actually quite a bit hotter than the ambient air (intake). Something like 30-40 degrees (fahrenheit) hotter.
The difference between these two temperatures is what makes the a/c unit work. If the difference between those two temperatures is only 10 degrees, help! This unit can barely work at all! It's barely cooling and internally, it's working its head off and everything is getting all heated up to accomplish not much of anything at all.
On the other hand, if the intake/output difference is say 40 degrees, then it is real happy and works well.
What you want to do is take in normal ambient temperature outside air into the intake--that is air that is as cool as possible and maximizes the difference between intake and output air temperature that we were just talking about.
What you DO NOT want to do is re-suck in the hot exhaust air that is 30-40 degrees hotter than the ordinary ambient-temperature air. It's not only 30-40 degrees hotter than ambient air, even more important it is exactly the same temperature as the output air.
The a/c unit needs a difference in temperature to operate, and if there is no difference, it can't work effectively. Smaller difference than it needs, and effectiveness goes down a lot.
So the dual-intake system is designed to do exactly that: maximize the coolness of air it is intaking, and reduce the possible amount of hot output that goes towards the intakes. It sucks in the cooler air from an 'angle' off the the right & left side while channeling the hot exhaust air to move at a good clip right out from the center of the unit.
Undoubtedly there will be some mixing and some of the hot exhaust air will eventually make it back into the intake ports. But by the time it has done so there will have been a lot of nice mixing with regular ambient-temperature outside air and so no great harm done.
Whereas if you just remove the whole louvre system the hot exhaust air is just going to go out the back and then be sucked right back in the intake area, with only a little mixing with ambient-termperature outside air before it goes back in the intake.
So that is a long explanation, but the upshot is, to some degree the dual-intake vent panel will definitely ensure that cooler air is being sucked into the a/c's air intakes, which will make the unit operate a lot better.
"Operate a lot better" translates to: Cools the room a lot more effectively, uses less power/electricity while doing so, better avoids overheating and damaging the unit.
So it will do all that to some degree.
What is hard to say without doing some real testing, is exactly how important that is.
Like it might cool a little better, save a little electricity, and last a little longer if you have the dual exhaust vent in place.
Or it might work a lot better, save a lot of electricity, and last a of longer if you have the dual exhaust vent in place.
Guessing, it is probably not a little or a lot, but in between--a moderate savings, moderately work better, moderately last longer.
Maybe there is an a/c technician with actual experience who can weigh in.
posted by flug at 1:12 PM on July 18, 2020 [8 favorites]
I think there's more possibility of crittters and larger light trash being sucked into it if you leave it off. It probably wouldn't be fun to have to remove a mouse or something or deal with a bird making a nest in it or other random things.
posted by AlexiaSky at 1:12 PM on July 18, 2020 [1 favorite]
posted by AlexiaSky at 1:12 PM on July 18, 2020 [1 favorite]
While I agree with Flug in the research, I think that removal of the grill will probably have less than a 10% impact on the effectiveness of the grill. Maybe like 3-4%.
posted by bbqturtle at 1:18 PM on July 18, 2020
posted by bbqturtle at 1:18 PM on July 18, 2020
It will make a difference in efficiency. But don't despair. You don't have to attach the grill to the sleeve, which limits the depth of the air conditioner. You can attach the grill directly to the air conditioner and slide the air conditioner farther out so it doesn't extend into the room.
See page 6 of the manual flug posted above. Or your own manual should have similar instructions for "direct mounting" of the grill. It may involve drilling four holes but that is pretty simple. It's like a 15-minute job if you have the necessary tools. You say it is on the first floor. Would be much more difficult if on a higher floor since you have to mount the grill from the outside.
It will make your air conditioner work better and save money on your electric bill. It's definitely worth doing.
In the mean time, it won't kill your air conditioner to run without the grill. It will just be less efficient.
posted by JackFlash at 5:16 PM on July 18, 2020
See page 6 of the manual flug posted above. Or your own manual should have similar instructions for "direct mounting" of the grill. It may involve drilling four holes but that is pretty simple. It's like a 15-minute job if you have the necessary tools. You say it is on the first floor. Would be much more difficult if on a higher floor since you have to mount the grill from the outside.
It will make your air conditioner work better and save money on your electric bill. It's definitely worth doing.
In the mean time, it won't kill your air conditioner to run without the grill. It will just be less efficient.
posted by JackFlash at 5:16 PM on July 18, 2020
As flug says, the purpose of the grill is to enhance the separation of the stream of air going out from the two streams of air going in. If you look closely at pictures of the grill he found (good work, by the way) you can see that the vertical flat pieces that make up the grill are twisted so that the outgoing air is pushed away from the sides toward the center, and so that the incoming air is taken from the sides and outsides as much as possible.
I wish I could see how closely the back of the AC pushes up against the bars, because if it's closely enough, you might be able to help considerably by lashing the grill to the outside of the bars with cable ties and, depending on the geometry, extending a couple of pieces cardboard back from the grill through the bars and into the body of the AC to prevent mixing which would otherwise occur in the space between the grill and the back of the sleeve. A space which is now occupied by the bars and would not exist if they weren't there.
I think one reason it works as well as it does without the grill is because the hot air tends to rise out of the reach of the intakes as soon as it emerges from the unit. Another might be that the grill adds a lot of resistance to the airflow both in and out, and without it you get more air throughput and the hot air can rise more easily, both of which would help.
posted by jamjam at 9:41 PM on July 18, 2020 [1 favorite]
I wish I could see how closely the back of the AC pushes up against the bars, because if it's closely enough, you might be able to help considerably by lashing the grill to the outside of the bars with cable ties and, depending on the geometry, extending a couple of pieces cardboard back from the grill through the bars and into the body of the AC to prevent mixing which would otherwise occur in the space between the grill and the back of the sleeve. A space which is now occupied by the bars and would not exist if they weren't there.
I think one reason it works as well as it does without the grill is because the hot air tends to rise out of the reach of the intakes as soon as it emerges from the unit. Another might be that the grill adds a lot of resistance to the airflow both in and out, and without it you get more air throughput and the hot air can rise more easily, both of which would help.
posted by jamjam at 9:41 PM on July 18, 2020 [1 favorite]
Hi, jamjam. From what I understand, the bars are on the window. So instead, the AC goes in a steel sleeve through the wall. Normally you attach the grill to the outside of the sleeve and then shove the AC into the sleeve until in is stopped by the grill.
The problem they have is the the depth of the sleeve through the wall is too short if they mount the grill on the outside of the sleeve. That leaves the AC projecting too far into the room.
The suggested solution is to push the AC out as far as necessary through the sleeve so it is flush with the inside wall, past the sleeve on the outside, and then mount the grill on the back of the AC instead of the back of the sleeve.
posted by JackFlash at 9:56 PM on July 18, 2020
The problem they have is the the depth of the sleeve through the wall is too short if they mount the grill on the outside of the sleeve. That leaves the AC projecting too far into the room.
The suggested solution is to push the AC out as far as necessary through the sleeve so it is flush with the inside wall, past the sleeve on the outside, and then mount the grill on the back of the AC instead of the back of the sleeve.
posted by JackFlash at 9:56 PM on July 18, 2020
So I thought as well, JackFlash, but how are they to push the air conditioner so far out through the window that it's flush with the inside wall? Wouldn't it run into the bars?
posted by jamjam at 10:07 PM on July 18, 2020
posted by jamjam at 10:07 PM on July 18, 2020
The bars are on the window so they can't use a window AC. The sleeve through the wall is a separate opening completely unrelated to the window and used only for the AC. There are no bars on the sleeve through the wall -- at least that is my understanding.
Here's what I'm picturing.
posted by JackFlash at 10:12 PM on July 18, 2020
Here's what I'm picturing.
posted by JackFlash at 10:12 PM on July 18, 2020
Best answer: It is through the wall, not window, but we put it in a window -- without the back grill.
I read that as saying it's in the window.
posted by jamjam at 10:15 PM on July 18, 2020
I read that as saying it's in the window.
posted by jamjam at 10:15 PM on July 18, 2020
Oh, sorry, then I completely misunderstood. They are taking a through the wall air conditioner and mounting it unconventionally in a window. Okay. Now I see the problem.
In that case, I agree with you. Put the grill on the outside of the bars. I would try filling up the empty space with foam weather stripping to divide the incoming and outgoing air.
posted by JackFlash at 10:22 PM on July 18, 2020 [1 favorite]
In that case, I agree with you. Put the grill on the outside of the bars. I would try filling up the empty space with foam weather stripping to divide the incoming and outgoing air.
posted by JackFlash at 10:22 PM on July 18, 2020 [1 favorite]
At first I read it just the way you did, and when you made your comment to me, my first reaction was 'damn— I knew I should have stuck with that!'
posted by jamjam at 10:28 PM on July 18, 2020
posted by jamjam at 10:28 PM on July 18, 2020
Response by poster: The a/c is in the window. (I should have said, "It's a through-the-wall type of a/c but we put it in a window"). It's pushed directly against the thick iron vertical security window bars. Putting the grill on the OTHER side of the bars (that is, outside) is a good idea, if we can figure out a place on the a/c to lash it to. thank you.
posted by DMelanogaster at 6:13 AM on July 20, 2020
posted by DMelanogaster at 6:13 AM on July 20, 2020
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posted by aramaic at 1:09 PM on July 18, 2020