How to air condition a FROG (finished room over garage)

I once had a 16' x 32' den, and the builder installed a General Electric PTAC a/c unit with heat strips like those commonly seen in hotels. They come in all sizes, including large units. We left it cut off when we were at work, but it'd cool or heat the room up in about 5 minutes. And it was very inexpensive to run.

A PTAC unit would work fine in a side wall over a garage. You just wouldn't want it facing the street where it would be unsightly. What's so good about them is that you cut a hole in the wall, install a standardized size metal jacket, and slide the PTAC unit in. Then just plug it in--no professional installation is required.
 
Bamaman said:
I once had a 16' x 32' den, and the builder installed a General Electric PTAC a/c unit with heat strips like those commonly seen in hotels. They come in all sizes, including large units. We left it cut off when we were at work, but it'd cool or heat the room up in about 5 minutes. And it was very inexpensive to run.

A PTAC unit would work fine in a side wall over a garage. You just wouldn't want it facing the street where it would be unsightly. What's so good about them is that you cut a hole in the wall, install a standardized size metal jacket, and slide the PTAC unit in. Then just plug it in--no professional installation is required.
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We had a screened porch connecting the house to the garage and never used it. About 15 years ago we had it enclosed into a playroom for the grandkids and installed a PTAC unit which works great to cool and heat the room. It has also come in really handy a few times, once when the central A/C unit went on the fritz during a major heat wave and two or three times when we had a major power failure. Cranked up the portable generator to power it and the fridge.
 
Does the room have a ceiling fan ? Plus you are talking to air conditioner guys during the most costly time . If you can wait until January you will save a bundle .Use fans in the meantime .
 
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Bamaman said:
300 square feet in an attic location would need a 12,000 btu heat pump/air conditioning unit. If it was installed in a basement, you could get away with 9,000 btu heat pump...
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I forgot to mention the above. A FROG is exposed on all sides to the ambient, and even the garage underneath is not the same as a room on a slab.

Thus, it is better to have a larger unit. And again, a modern AC/heat pump will reduce its speed once the desired temperature is approached. It then provides continual cooling/heating as a much smaller unit. The difference in equipment cost is not that much.

On the other hand, if you install an undersized unit, it does not have a "turbocharged mode".

If this is a house that I intend to own for a long time, I would not scrimp and use a window AC. A minisplit is the way to go, and it provides heating in the winter too.
 
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Thanks for mentioning that. I will ask the next contractor about the temperature sensing/speed reduction. They do tend to run right over us as if we know nothing. Mr. A. is uncomfortable talking about mechanical things, and I sense some talking down to the little lady is going on as well. More than I expected, frankly, nowadays. Maybe it is a Florida thing.

NW-Bound said:
I forgot to mention the above. A FROG is exposed on all sides to the ambient, and even the garage underneath is not the same as a room on a slab.

Thus, it is better to have a larger unit. And again, a modern AC/heat pump will reduce its speed once the desired temperature is approached. It then provides continual cooling/heating as a much smaller unit. The difference in equipment cost is not that much.

On the other hand, if you install an undersized unit, it does not have a "turbocharged mode".

If this is a house that I intend to own for a long time, I would not scrimp and use a window AC. A minisplit is the way to go, and it provides heating in the winter too.
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It does have a fan, and it is not enough.

It does not seem like they are all that busy. They seem eager for business. Do there tend to be AC sales in the winter? We have plenty else going on, could wait if it would pay off.

Moemg said:
Does the room have a ceiling fan ? Plus you are talking to air conditioner guys during the most costly time . If you can wait until January you will save a bundle .Use fans in the meantime .
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It would be a better idea to correct the system you have then to put in another mechanical system to make up for its inadequacies. I would research installing a zoning system, they work wonderfully. Not to mention that if you add a system you have now created something else that needs maintenance, repairs and eventual replacement.

If you end up moving forward with a mini split I would highly suggest you hire a local Hvac guy to provide and install it for you. I have been involved in the installations of these units where it has gone terribly wrong. They are plump full of electronics and one little thing can be a nightmare. If you order it yourself and hire an hvac guy to install then experience the inevitable problem his responsibility was only the installation which is pretty basic. He certainly won’t do any warranty work or troubleshoot problems on a unit that he didn’t provide without being paid. This leaves you trying to sort out the chaos with the retailer. It never ends well.
 
The room is above the garage, which is not air conditioned, all the hot air is coming up from the garage. Is there good insulation above the garage ceiling? That room would need more ducts and air flow than other rooms, but that's not something most builders include.

A window fan to remove that hot air might help, perhaps an attic fan above this room as well. Other than that, a dedicated unit for that room isn't a bad idea.
 
I people are trying to rush you and talking down to you, maybe it’s time to seek out a different type of person. Maybe see if a HVAC person could come just to do an evaluation. Maybe the electric utility could recommend someone. Point is to try to find someone to advise you that has no financial interest in trying to sell you anything other that their professional advice. In Florida, maybe there’s some good HVAC guys that have retired that consult on the side. I agree with a few other comments. It’s probably a good idea to look at the entire system to see what your best options are. It would suck to put money into this room only to have you main unit go. If you have to replace the main unit, then a zoning option could be way more cost effective. Done forget energy cost in the process.

Our utility companies do energy audits for free. That may be a place to start.
 
In my prior home we had ~ 420 ft2 FROG that was serviced by one of the downstairs 5 ton AC systems with no upstairs thermostat. Initially the builder added a thermostat and played around with the ductwork to try to get it cooled, but that did not work. Ultimately they installed a separate 1.5 ton unit and added another duct and return and then we had heaven. It's unusual that a builder would go this far to make the new homeowner happy, but I guess they got sick of my complaining about an inadequate initial design.
 
Amethyst said:
It does have a fan, and it is not enough.

It does not seem like they are all that busy. They seem eager for business. Do there tend to be AC sales in the winter? We have plenty else going on, could wait if it would pay off.
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They are more willing to bargain in the winter .Plus by then you will e able to get some recommendations from neighbors .
 
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We had pretty much the same situation in the last house we lived in for 30 years. We had a room over the garage that was cold in winter and hot in the summer. I solved the problem for less than $25 by adding a duct booster. A duct booster is essentially a small piece of duct work with a fan in it. I also wired a switch to it so it could be turned off if we didn't plan on using the room for a long period of time. Might be worth a try before spending 3K.
 
FROG has two ducts. Do we know for certain that one duct is a return?

The duct or vent booster could help significantly. There are some that sit on a floor vent, and come on automatically when air flow is sensed. Otherwise you need to install inline and find power for it.
A transom door at foot of stairs would help a lot. May be called a folding door.
Attic fan is a must, assuming there is attic space.
 
Amethyst said:
#2 insisted that 9000 Btuh was better for the room than 12000 Btuh, because the larger unit would cool the room faster, which would cause more condensation and thus encourage mold! It sounded goofy, although the guy seemed like a straight shooter otherwise.
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I saw this just now, and do not understand this.

It is not possible to cool without causing condensation, besides dehumidifying is also desirable. Here in the arid Southwest, I put a bucket under the drain line out of curiosity and catch more than 1 gallon a day.

In humid places, people often complain of mold growing in AC. I saw gross videos on Youtube. I don't know how it can be prevented.

PS. A booster fan in the existing duct is a possible low-cost remedy, if the main AC is sufficiently sized to handle the load. If it runs all the time now, then it's too small. If it turns off even in the midday, then it has enough capacity.

My single 5-ton AC runs nearly continuously without turning off in the hottest day of summer. I am glad to supplement it with a minisplit to the downstairs, because we do not use the 5 rooms upstairs much other than my electronic hobby room. I am able to raise the thermostat and save quite a bit of money. I could perhaps turn it off altogether, and let the upstairs get to more than 100F.
 
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Out of curiosity, I just checked humidity in several places as of this writing.

Phoenix: 63F dew point (we have entered the rain or monsoon season which starts in late summer)
Fort Lauderdale: 75F dew point
New Orleans: 79F dew point
Los Angeles: 59F dew point

I have measured the air blown out of the AC as cool as 55F. That explains the condensation I saw and described earlier.

I went out to look at the drip line. The water is coming out at a rate of almost 2 drops/second!
 
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Step one is to do a heat load calculation for the FROG. If the folks who came out didn't do one (They might call it a "Manual J calculation"), you can do it yourself in just a few minutes. I like this calculator: HVAC Load Calculation - Maunualj - Whole House Loadcalc

Don't overlook that garage underneath--it could add a lot to the heat load of the FROG, especially if there's no insulation under the floor of the FROG.

We haven't talked about heat-- is the present system for the house doing an adequate job of keeping the FROG comfortable in the winter?

target2019 said:
FROG has two ducts. Do we know for certain that one duct is a return?
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Yes. If there's no return air (through a duct, through an undercut door, through a grill in the door, etc), then neither the heating nor cooling will be effective.

Before even considering using your present HVAC system, you'd need to know if the existing system has sufficient capacity, which is another set of calculations (or, you could base it on experience if you know the duty cycle of the AC system on your very hottest days. If it is running continuously, then it can't handle the additional load of the FROG). To make the temps in the FROG right, you'd need to add a separate zone to your present system IF it has sufficient capacity (so a separate thermostat, mechanical dampers, etc). It's still a compromise, and your system will be running at times when it otherwise wouldn't need to. On the whole--I wouldn't bother with that. I'd just get new equipment.

To restate some already said stuff, you have 5 approaches available:
1) Integrate the FROG into your existing HVAC (heating and cooling) system ductwork. For reasons above, I wouldn't do that.

2) Window AC unit for the FROG. These can be installed in a window OR a newly framed opening in an existing exterior wall (if the FROG has one--if it is all hip roof overhead, then you don't have this option). Cutting a new opening (vs using a window) means you don't lose any of the existing light, and you can mount the unit fairly high (which is best for cooling). Yes, you can buy a special unit designed for wall mounting, but a mass-market window unit will work just as well and will be less expensive. If you don't need to heat the FROG, this is a very inexpensive way to go, and the efficiency isn't bad. As stated--when the unit crumps out in a decade or so, you go get another one and you are done. Very simple. It will be a bit noisier than a minisplit, but it might not be a problem.
3) Minisplit: A deluxe answer and probably the answer most likely in an upscale home. When any part of it needs fixing, there will be a pricey service call. More efficient than a window unit, but the payback in utlity cost would for the minisplit would probably exceed the life of the equipment.

4) Minisplit with heat pump: Like Option 3, but with heat. More $$.
5) Window unit with heat: Like Option 2, but with a built-in heater. These are typically electrical resistance heaters ("heat strips"), so they are expensive to run. If your existing ductwork does the heating job, but not entirely well, this could be an option. Also, if you just need to heat for a month per year, or several hours per day, this might be fine.

You could also use a through-the-wall PTAC unit--which has cooling and heat-pump heating in one piece of equipment. These are common in motels, and cost less than $1000 for the equipment. Look for a quiet one. Examples:https://www.alpinehomeair.com/viewcategory.cfm?categoryID=248

A FROG can be some really useful space. We had one when we lived in NC, and DW and I spent a lot of time there--puttering around on our projects, etc.
 
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yes, it does run like crazy when it's hot. The original owners had this one installed - it's not the original system. The system did pass inspection, but it's hard to know until you really live there. The house is somewhat upscale, but I think their priorities were elsewhere.

samclem said:
If it is running continuously, then it can't handle the additional load of the FROG).

2) Window AC unit for the FROG. These can be installed in a window OR a newly framed opening in an existing exterior wall (if the FROG has one--if it is all hip roof overhead, then you don't have this option).
>>Roof is a cement tile hip roof - a very hippy one, ha. I don't think there is any wood framing in the walls (all CBS with stucco on outside and drywall inside) but I could be wrong, so it's worth checking out.

You could also use a through-the-wall PTAC unit--which has cooling and heat-pump heating in one piece of equipment. These are common in motels, and cost less than $1000 for the equipment. Look for a quiet one.

>>Any time we've stayed in a motel, the unit has been very noisy indeed. Trying to avoid that! The contractors claimed they have mini-splits in their own homes and that they are very quiet. But I haven't been in their homes, so how do I judge?

Examples:https://www.alpinehomeair.com/viewcategory.cfm?categoryID=248
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If the existing AC does not have enough capacity, then the minisplit is the only option.

A PTAC requires knocking out a huge rectangular hole, and Amethyst already said the walls are masonry. There's also no window, and there goes the windows AC option.

The refrigerant lines require a hole around 1.5" in the wall. They are actually smaller than that, but the bundle is usually covered in insulation foam of that diameter.
 
Amethyst said:
yes, it does run like crazy when it's hot. The original owners had this one installed - it's not the original system. The system did pass inspection, but it's hard to know until you really live there.
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That's actually a good thing--you've apparently got an AC system that is sized right for your home. It probably does a good job of keeping your indoor humidity low, something that oversized AC systems typically aren't good at.
NW-Bound said:
If the existing AC does not have enough capacity, then the minisplit is the only option.
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Yep, and it may be a good one. Doing the heat load calculation can help you decide on the system size--get what you need, but not larger.

As a bonus, having a completely separate AC system will give you a spot to hunker down for a day or so[-] if [/-]when your main AC unit crumps out. Pretty nice, and could save you big bucks over having to go with the overpriced "we can install a replacement right now" option.
 
As always, I so appreciate everyone's thoughtful, helpful comments. Please keep them coming - I will review and digest before talking to any more contractors.

I did find, and talk to, the contractor who installed the current a/c system for the previous owner. I explained that the system was struggling, and asked (politely) how he determines the size of the system to install. He said, "As I recall, we just replaced the system that was already there." In addition, he remembered the previous owner complaining about heat in the Frog. He provided an estimate for a mini-split, and never heard back.

His attitude about sizing doesn't seem terribly professional, does it? Then again, it's possible he did not bother to analyze and size the system, b/c the previous owner just directed him to "replace what's there."
 
Oh, my. That heat load calculator asks for a lot of info that we can't lay our hands on. Especially insulation - except for the attic, which has about 16-18" of loose insulation, there's no telling what's in the walls, floors, ceilings. Even the garage under the Frog is drywalled.

samclem said:
Yep, and it may be a good one. Doing the heat load calculation can help you decide on the system size--get what you need, but not larger.
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