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

[NW-Bound]

I just installed a minisplit myself, and did all the work.

It's an 18,000-BTU/hr AC/heat pump, with a SEER of 21. I paid $1250 buying directly from the US manufacturer, and this price included a long 33-ft refrigerant line due to the indoor and outdoor units being separated by a fair distance.

This unit is to supplement the central AC of 5 tons (60,000 BTU/hr), and it works great to off-load the big unit.

New inverter type AC/heatpumps will vary the speed of the indoor blower as well as the outdoor blower and compressor, and that's how they have their high efficiency. They don't run at one speed like the old ACs, which only turn on or off.

My unit runs continuously due to the ability to slow down at night. During the day, it can cool the ground floor of the house by itself, which is perhaps 1,800 sq.ft. It works way better than I expected!

PS. The reason for the minisplit is so that I can use the juice from my off-grid solar system. I cannot run the big AC with the solar, but this minisplit is no sweat for it. I am looking to install a 2nd smaller minisplit later this year to use more of the solar power.

PPS. When it's 115F outside, the unit runs full-speed and can cool the ground floor to 81F only. This is still quite comfortable to me, due to the low humidity of the Southwest.

[target2019]

I'd look at the entire Hvac situation. Age of old system, sizing, cost to operate.
Existing system pushes air longest distance to Frog. Is it oversized? Shutting off two ducts may mean it is now oversized.
Fact is that cold air pushed to Frog (insulated over/under?) falls and returns to first floor. If this is air with humidity, it taxes existing system. Adding another system will improve the environment. But other deficiencies will remain. Bills will increase, and things do break.

[Just_Steve]

I would just create a separate zone, probably cost less than 1k.

[Bamaman]

My HVAC guy has personally switched over to a mini split heat pump in his house. I see them in use all over the world.

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.

See HeatandCool.com for unit pricing. The Daikin 12,000 btu heat pump system is only $890 including shipping. It is a premium brand like LG, Mitsubishi and Fredrich and not some generic brand. Definitely better quality than a Haier.

I think you'll admit that the prices you have include $2400-2600 installation which is truly excessive. The refrigerant is already included with the mini-split. I'd order the mini split directly and then contact an independent HVAC contractor to get it installed.

[Amethyst]

For those who've suggested a window A/C, the FROG has two skylights and an exit door (to a small deck). There is no window as such.

[travelover]

Quote:

Originally Posted by Amethyst For those who've suggested a window A/C, the FROG has two skylights and an exit door (to a small deck). There is no window as such.

There are through the wall air conditioners. I'm not crazy about how they look, but they are relatively inexpensive. https://www.homedepot.com/b/Heating-...s/N-5yc1vZc4md

[Bamaman]

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.

[REWahoo]

Quote:

Originally Posted by Bamaman 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.

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.

[Moemg]

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 .

[NW-Bound]

Quote:

Originally Posted by Bamaman 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...

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.

[Amethyst]

This is a concrete block construction house. Not sure how good it would be for structural integrity. Think hurricanes....

Quote:

Originally Posted by travelover There are through the wall air conditioners. I'm not crazy about how they look, but they are relatively inexpensive. https://www.homedepot.com/b/Heating-...s/N-5yc1vZc4md

[Amethyst]

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.

Quote:

Originally Posted by NW-Bound 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.

[Amethyst]

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.

Quote:

Originally Posted by Moemg 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 .

[Amethyst]

What does that entail?

'

Quote:

Originally Posted by Just_Steve I would just create a separate zone, probably cost less than 1k.

[427Vette]

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.

[MichaelB]

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.

[Jerry1]

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.

[eytonxav]

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.

[Moemg]

Quote:

Originally Posted by Amethyst 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.

They are more willing to bargain in the winter .Plus by then you will e able to get some recommendations from neighbors .

[freedomatlast]

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.