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

Our house, like many in the south, is one story with a finished room over the (finished) garage. The FROG has two ducts leading from the central A/C, but no thermostat. It's always 5-10 degrees warmer than the rest of the house. There is no door closing off the staircase from the first floor utility room to the FROG.

I want to use the FROG as a studio, as it is a nice size (300 square feet) and has plenty of natural light.

We've interviewed 2 HVAC contractors, with a third coming next week. Both recommend installing a mini-split ductless AC unit in the FROG and closing off the ducts. But their recommendations differ, so it's hard to compare offers. Could some of you help, please? Also if you wouldn't mind, are there any questions to ask Contractor #3?

Contractor #1 offered a 1-ton (12000 Btuh) unit. Contractor #2 says a 3/4 ton unit is plenty.

Contractor 1: New Install - Haier 1Ton 16SEER Mini Split 1.0 $3,500.00
Install new Haier 1Ton 16SEER, Mini Split Air Handler and Heat Pump Condensing Unit.
Condenser Model 1U12TE1VHA, Serial Air Handler Model AW12TE1VHA, Serial AHRI 10191422
12,000 Btuh Cooling 12,000 Btuh Heating
Also Includes: Equipment Pad 1/4, 3/8 Copper Line Line Set Cover Vinyl Tube Drain line Permits Electrical 10 Year Parts Warranty

Contractor 2: (Capitals theirs) ESTIMATE - DUCTLESS MINI SPLIT 1.0 $3,300.00
MANUFACTURE: HAIER,
9000 BTU, 16 SEER
M# 1U09TE1VHA M# AW09TE1VHA
REMOTE CONTROL
COPPER LINE SET LINE COVERS SLAB ELECTRICIAN 10 ALL PARTS WARRANTY 2 YR LABOR WARRANTY

Thank you,

Amethyst

Nothing to add for date #3, but I see that only #2 calls out labor warranty - that's important. The longer, the better. Things can fail long after the install due to shoddy work. They need to be on the hook for that.

Mini-split is the way to go. As with land lines and cable, the developing world is bypassing ducted systems (expensive and inefficient) for split / mini-split.

We have a room that runs hot due to sunlight exposure. When the current window AC dies, we're going the mini split route.

It looks like both units are of the same series, with one slightly larger than the other (12000 BTU/hr vs. 9000).

The smaller one is supposedly large enough for 300 sq.ft., but being of the modern inverter type, both units can slow down the speed to accommodate a lesser demand. The larger unit will have some spare capacity.

The price difference between the two units is not that much if you purchase them yourself, probably $200, with no change in installation requirements. I am sure that if you demand a 12000 BTU/hr from the 2nd contractor, he can do it. If you are a good negotiator, perhaps you can get it without even paying the extra $200.

It boils down to the reputation of the installer, as the quotes are amazingly close.

#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.

Age old HVAC debate. Both units will cool the space. The smaller unit will run longer. It will dehumidify the space more. It will take longer to cool the space down if you let the space get warm. The larger unit will cool the space faster, it will probably not dehumidify the space as much. The larger unit will probably use a little more electricity.
HVAC engineers usually pick the smaller unit. HVAC installers usually pick the larger unit. The engineers are correct that the smaller unit is more efficient and removes more moisture. The installers say, yeah, but I don't get complaints or have to go back to an installation if I put in the larger unit. Customers like a space to cool down fast. Both are probably correct, just different requirements.

In the south, the value of dehumidification can't be overstated.

There are controllers with both a thermostat and a humidistat. I would ask them both if these types of controllers work with their quoted units and if so, what is the difference.

I think that is what the contractor said, too. Since we would plan to use the FROG like a "real" part of the house, we would keep it at the same temperature. And dehumidification is definitely a goal.

OK...I'll tell them I've been doing some reading and have a few questions :-)

I would try working with the existing ducts before I started writing big checks. Maybe add some dampers to ducts that feed the rest of the house, forcing more air to the FROG. Maybe do something similar in the return air ducting so more/all of the return air comes from the FROG. Maybe a couple of near-silent booster fans in the ducts to the FROG. Maybe set the HVAC unit fan to run continuously? Our HVAC fan runs all the time at a low/economical rate and the circulating air makes a big difference in making the house temp even.

Any HVAC contractor can discuss these options and help you decide what/if to try, but they are naturally going for the big ticket unless you pull them back.

A friend of ours just replaced his regular HVAC and instead of adding a split system unit the installing contractor "split" the traditional system using electrically activated dampers and 2 thermostats. If the upstairs calls for AC and the downstairs is already cool, the system closes the first floor supply vents and all the cooling is directed to the upstairs area. Same if the reverse happens and the first floor calls for heat and the upstairs is warm due to convection.

Of course in this instance the differential in square footage is not as drastic as in your case.

I would go with the larger if you plan to use the room less and the smaller if more. If you plan to keep at temp go small. If you only plan to AC when in there for a few hours then go I would go big to chill fast.

I'd get a third estimate. Anyone can buy this for $1500, so you are being charged $2000 to install a $1500 mini split, which is a one day job or less. That is $250 an hour. Also, 16 SEER is not particularly good.



https://www.acwholesalers.com/Mitsub...NA/p65347.html

I can tell that I'm not in the same league as you all! I'd probably just buy a window air conditioner and leave it at that. :rofl:

I admit that the rest of my house does have central AC. But this is just one room that isn't intended to be used a whole lot from what I am reading between the lines.

Actually not a bad idea if one can live with a window AC.

This would be my opinion too. I had a three season room changed to a four season room and all the did was run two ducts, which you already have, and run a booster fan on one line. It cooled and heated the space just fine.

The idea about setting up a separate zone is good too. Probably the next step up in cost but still cheaper that the new unit you’ve had quoted.

Also, if there’s any way to install a door to keep the cooler air from escaping and the hot air from entering the space, that would help a lot.

For a test, you could shut down all the other dampers in the house half way and run the fan constantly. If that gets the room comfortable, there’d be no need to get the new additional unit.

As for the difference in sizing, I found the quote below here: https://www.minisplitwarehouse.com/p...ier-mini-split

So, at 300 sq ft you are at the border between the two sizes.

I would normally agree with other posters and say that the smaller one will provide better de-humidification, but since the cold air will naturally flow out of the room to the utility room and main house, and then be returned to the main system, I am not sure that is as big a concern.

So, if you intend to have the mini-split maintain the room at the same temp as the main house, I don't think it matters much. If you intend to maintain the FROG at 10-15 degrees higher, and only tun it down when using it, I would definitely want the bigger unit.

I'd go window unit too. Way cheaper, handyman job, when it breaks get another one.

Perhaps consider a wall-mounted air conditioning unit like this. Not endorsing the brand, but including the web link for illustration. Might be a better option than a window unit.

https://www.mitsubishicomfort.com/pr...ng-and-cooling

I agree! In fact, I have exactly the same situation in our house and a 200 dollar window unit does just fine. Now, mind you, there is some noise, but truth be told, the mini split systems are not much quieter. Unless it is used as a bedroom, I'd go with a window unit.

That is a mini-split, which the OP is looking at (different manufacturer).