Question for the HVAC gurus

I'm not sure exactly what they were thinking when they designed this house, but the upstairs AC isn't particularly adequate. In most of the upstairs rooms, the cooling is just fine (2600 sq/ft, dual-zone central air). However, the theater room/spare bedroom always seems stagnant and nowhere near as cool as the rest of the house.

There are three registers in the room, all ceiling mounted, with no returns. The room is over the garage, and has no attic crawlspace over it, so I'd imagine the lesser insulation isn't helping matters any. When the home was inspected, he verified the temperature drop at the registers was adequate, but even though the room is constantly dark and light-controlled (all windows are blacked out), it's still uncomfortably warm in there.

Normally, with the AC set to 74-75, it will have a hard time driving the upstairs below 76-78°F at best, but it's still relatively comfortable. The theater room is noticably warmer, and the stagnant air doesn't help matters. Turn the projector and electronics on for a while, and it exacerbates the problem.

Is there anything I can do to help promote cooling in this room without having to rip half the house apart? Should I look into having the upstairs unit sized any differently? Are there any options that don't involve having to run more duct work? I'm about to just give up and plop a barrage of Lasko floor fans all around the room.

Wow. Talk aobut deja vu all over again. I JUST TODAY resolved a similar problem with mini-MS's room. His room always was warmer than the rest of the house. As I was cleaning the evaporator coil, I noticed that the damper leading to his room was partially closed. I opened it completely and, voila, his room is as cool as the remainder of the house.

Check your dampers, look for leaks (ongoing fight for me and mastic is in my future), and get it did. YMMV

edit: oh yeah, I 'll be blowing in about 30 bags of Green Fiber insulation from Lowe's as soon as I can finish some required prework (lay down a walking path / storage place, re-inforce future fan ceiling box, etc...).

I'll have to head to the attic tomorrow and check it out. I don't think that's the problem though, as the air seems to be blowing on par with the other rooms when you get close to the registers. The fact that the room is so large doesn't help (19x21).

Definitely not a damper situation. Unless there are inline dampers that I can't see (no crawlspace access), it's dependent entirely on the registers in the ceiling. Did feel two considerable leaks blowing though, so I'll be off to pick up some foil tape this afternoon. None of leaks were at the duct work, but rather out of a faulty grommet and a removable panel on the handler itself. The main distribution duct on top of the handler is pretty cold and sweating, so I think I'll wrap that thing in some Dow foam while I'm at it.

Geezum petes. Talk about HVAC conundrums. I spent the majority of this weekend in the attic. Well, the majority of my pre-noon time in the attic as being up there after 11 AM begins to be uncomfortably hot. Anywho, among other things, I've been cleaning and chasing leaks. I'm a bit perturbed I didn't do this a loooooooong time ago, but I finally got around to inspecting the air handler... post evaporator. Every single duct coming off the handler has a leak at the port itself. I fixed what I could with foil tape, but I really need to get some mastic or something to take care of it for good. Trying to shape the tape onto the duct and onto the flat handler at the same time is a pain in the nads.

I've read ideas of using sheetrock mesh tape as a backer and applying mastic on top for a good leak stopper, but is there anything like mastic in a caulking tube at Lowe's or Home Depot I could use for smaller leaks? I can't say I've found anything like that before. Any help is appreciated.

I don't know if it's at a local big box store, but they do make mastic in a caulking gun. Primary use is for repairs around pools.

If air can't get out it wont go in. Try leaving the door open so the cool air will get pulled to the return intake. Also, sounds like you have one thermostat for a two level house. In my experience this has/will never work, especially if you have a room over a garage with hot surfaes on all four sides. Its not a cheap option but can you add a mini split ductless unit to the room? If so, and you cut off those three supplies, it will help the rest of the upstairs stay cooler.

badal said:

If air can't get out it wont go in. Try leaving the door open so the cool air will get pulled to the return intake. Also, sounds like you have one thermostat for a two level house. In my experience this has/will never work, especially if you have a room over a garage with hot surfaes on all four sides. Its not a cheap option but can you add a mini split ductless unit to the room? If so, and you cut off those three supplies, it will help the rest of the upstairs stay cooler.

Click to expand...

Return intake is out in the hallway. Leaving door open/closed seems to have no affect on things whatsoever. There are separate t-stats/zones for the upper and lower levels. The upper definitely struggles to maintain temperature, but the theater room is appreciably warmer than the other rooms. The t-stat is not located in that room (its in the hallway), but the upstairs AC almost never shuts off until the early hours of the morning.

To add a little air movement, if you like to keep the door closed, put in a vent above the door, or even one with a quiet fan. If the room is good with the door open all the time, then you just have an air flow problem. If not, then...

check out www.ornl.gov such as http://www.ornl.gov/info/ornlreview/rev28_2/text/duct.htm for this topic.

My research and experience:

If you don't have at least 12" of insulation add some so that you have at least 16-20". http://www.ornl.gov/sci/roofs+walls/insulation/ins_06.html

Tape all leaks with aluminum foil tape - be very, very generous with the tape. Then wrap in insulation and tape.

Vacuum out all of your ducts - get one of those duct/dryer vent cleaning kits with the chimney-sweep-like brush. (Clean your dryer vent too.)

Pick up a cheap IR laser thermometer (I got one for $15-20), and see what the temperature of the wall are. You may have a gap in insulation or little or none at all.

If you need a new roof any time soon, look at one with a high infra-red reflectivity.

Would it be worth while getting an HVAC guy out there? I can file a claim for $100 and have a guy show up under my home owners warranty. Cleaning the ducts will be tough, as the flex duct is probably a good 20-30 feet in length.

is the bonus room over a garage?

Road Guy said:

is the bonus room over a garage?

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Yes it is. Garage is finished/drywalled, and not air conditioned.

thats probably the biggest problem, my daughters bedroom is over the garage, and with the heat build up in there our HVAC folks when we repalced our upstairs unit a few years ago told us just to get used to it. We even upsized the unit at the time from a 2 ton to a 3 ton, and it made some difference but not much..

we did redo the insulation above the bedroom ceiling, but more than likely there probably isnt much in the floor beneath the bedroom (your theatre room) I didnt want to tear down the sheetrock in the garage to redo the insulation.. Its also freezing in the winter...

I've seen these AC units that are like a window unit but they fit nicely in the wall, but have to have an outside air source that work pretty well, our neighbors house has a similar room and they bought one and had it put in, they use it as a TV room and they said its great in the summer, and still cold in the winter..

What size ducts are serving the space? You said three runs, but are they 6" or 8".

Also, yes, you can get separate ductless systems, but that is a noisy solution for a theatre room.

Can you get into the crawl space behind the knee wall? Consider a separate ducted system for that space alone. Place the airhandler behind the knee wall, and a good HVAC guy should be able to snake a handful of runs between the gypsum and roof. Place a return behind your screen, and place a slotted grille in the screen wall. That way you directly pick up the heat off your electronics and keep them cool, and places what should be the noisiest component behind an acoustical barrier (somewhat).

That's my thoughts. As you're not concerned about heat when the system is operating, there is potential for energy savings when you're not using the space.

Just a thought.

Best I can tell (from the attic crawlspace, there is a fire stop between the attic and where the bonus room would be,) is that there are two 8" lines going into that room, and one of them has to split somewhere over the bonus room. We did cut an access panel just to be able to see into the bonus room ceiling, but there's no way to physically get up there, and even seeing up there is a task because it would require removal of the screen wall to get a ladder back there.

Unfortunately, there is no knee wall in this room (ceiling slope doesn't go all the way to the floor), so they would have to put a second handler up in the attic. I'd imagine they could even reuse most of the existing duct runs, and just add a fourth register. Wonder how much a second AC unit and handler would run me installed up there?

Along related lines, ballpark estimate, what kind of savings going from a 1991 AC uniti to a new one. I hear they gained a lot of efficiency the last 20 years, but haven't really looked into them.

Supe said:

Best I can tell (from the attic crawlspace, there is a fire stop between the attic and where the bonus room would be,) is that there are two 8" lines going into that room, and one of them has to split somewhere over the bonus room. We did cut an access panel just to be able to see into the bonus room ceiling, but there's no way to physically get up there, and even seeing up there is a task because it would require removal of the screen wall to get a ladder back there.
Unfortunately, there is no knee wall in this room (ceiling slope doesn't go all the way to the floor), so they would have to put a second handler up in the attic. I'd imagine they could even reuse most of the existing duct runs, and just add a fourth register. Wonder how much a second AC unit and handler would run me installed up there?

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Then you've probably got at a maximum 400 CFM serving that space. With the size and limitations, yeah, that's gonna be pushing it.

I'd have to put some numbers too it for heat loads, but I'd be willing to bet it could support a two ton system easily. You'd need to add two more 8" runs to support the airflow for this system. If you can locate the air handler close, you could take a 8" flex line off a short trunk line off the air handler to minimize cost.

Actual equipment cost for a 13 SEER HP (where are you again? Carolinas, right?) split system of a well known brand is probably...roughly $2500. You'll most likely have at least a 50% mark-up on that. Labor and materials are probably going to run you another $1100 - $1800.

You should probably get into this somewhere between $4500 and $5500 for a Trane, Rheem, Carrier, etc.

Might can get it for $3500 - $4500 for a Heil, Goodman, Janitrol, etc.

Capt Worley PE said:

Along related lines, ballpark estimate, what kind of savings going from a 1991 AC uniti to a new one. I hear they gained a lot of efficiency the last 20 years, but haven't really looked into them.

Click to expand...

It's a little hard to quantify. I'd be comfortable giving you a ballpark figure of somewhere between (dependent on your personal temperature preferences, cost of electricity, etc.) $15 and $30 per power bill.

First of all, a unit from 1991 not only had lower efficiency than what is required today, it is also probably significantly degraded from when it was first installed. So, there is a greater gap in efficiency than you would think.

However, be wary of this high SEER stuff. You have EER and SEER for efficiency ratios. EER is a more accurate representation of actual power use, because the requirements for determining power usage are more similar to actual usage. SEER is determined at a lower ambient temperature. Thus, the work on the compressor is less. A lot of manufacturers will use two stage compressors to get a high SEER, but when in a more likely condition (such as those used for EER calculation), the second stage is typically a hog. This happens on a LOT of new equipment, and is the reason that a lot of people have been burnt with this ridiculous 21 SEER equipment that would not qualify for the energy credits.

In short, yes, you'll save a noticeable amount of money, and look at EER instead of SEER.

jmbeck said:

Supe said:

Best I can tell (from the attic crawlspace, there is a fire stop between the attic and where the bonus room would be,) is that there are two 8" lines going into that room, and one of them has to split somewhere over the bonus room. We did cut an access panel just to be able to see into the bonus room ceiling, but there's no way to physically get up there, and even seeing up there is a task because it would require removal of the screen wall to get a ladder back there.
Unfortunately, there is no knee wall in this room (ceiling slope doesn't go all the way to the floor), so they would have to put a second handler up in the attic. I'd imagine they could even reuse most of the existing duct runs, and just add a fourth register. Wonder how much a second AC unit and handler would run me installed up there?

Click to expand...

Then you've probably got at a maximum 400 CFM serving that space. With the size and limitations, yeah, that's gonna be pushing it.

I'd have to put some numbers too it for heat loads, but I'd be willing to bet it could support a two ton system easily. You'd need to add two more 8" runs to support the airflow for this system. If you can locate the air handler close, you could take a 8" flex line off a short trunk line off the air handler to minimize cost.

Actual equipment cost for a 13 SEER HP (where are you again? Carolinas, right?) split system of a well known brand is probably...roughly $2500. You'll most likely have at least a 50% mark-up on that. Labor and materials are probably going to run you another $1100 - $1800.

You should probably get into this somewhere between $4500 and $5500 for a Trane, Rheem, Carrier, etc.

Might can get it for $3500 - $4500 for a Heil, Goodman, Janitrol, etc.

Click to expand...

Yes, North Carolina, so it gets and stays pretty warm for quite a while. I honestly don't think running additional duct work would be too bad if need be. A quick sawzall job to that firewall to make room for two more ducts (which is all they did to begin with) and that access panel I cut in the ceiling would make it relatively easy to snake through there. Unfortunately, the handler would have to be even further away than the existing one.

jmbeck said:

Capt Worley PE said:

Along related lines, ballpark estimate, what kind of savings going from a 1991 AC uniti to a new one. I hear they gained a lot of efficiency the last 20 years, but haven't really looked into them.

Click to expand...

It's a little hard to quantify. I'd be comfortable giving you a ballpark figure of somewhere between (dependent on your personal temperature preferences, cost of electricity, etc.) $15 and $30 per power bill.

First of all, a unit from 1991 not only had lower efficiency than what is required today, it is also probably significantly degraded from when it was first installed. So, there is a greater gap in efficiency than you would think.

However, be wary of this high SEER stuff. You have EER and SEER for efficiency ratios. EER is a more accurate representation of actual power use, because the requirements for determining power usage are more similar to actual usage. SEER is determined at a lower ambient temperature. Thus, the work on the compressor is less. A lot of manufacturers will use two stage compressors to get a high SEER, but when in a more likely condition (such as those used for EER calculation), the second stage is typically a hog. This happens on a LOT of new equipment, and is the reason that a lot of people have been burnt with this ridiculous 21 SEER equipment that would not qualify for the energy credits.

In short, yes, you'll save a noticeable amount of money, and look at EER instead of SEER.

Click to expand...

Oh, crud...I was hoping for more of a savings than that. Running the AC costs about 200+ a month. The AC pretty much runs constantly because it is an old house, and the AC doesn't hold against the heat. Last summer I don't think it turned off for close to three months. No exaggeration since it didn't go below 75 degrees for that long.

I may go for a larger unit. House is about 1400 ft^2, and we like it about 72 degrees. Any guess as to sze/cost range?

Thanks for the EER/SEER clarification. I definitely was planning on staying away from anything that had multiple stages or variable speed.

Thanks!