Difficult installation question and much more.

[woodlandfarms]

We live in Los Angeles, specifically the Sherman Oaks area (long warm summers but generally cool nights). We own a 1600 sq ft 50's modern home with vaulted ceilings and lots of glass. We have updated everything insulation wise (windows, walls) but the vaulted roof and that is coming shortly. Oh, half our house is Vaulted, the other half has attic space with a max of 3 feet of headroom.

So, the combo AC / Furnace is dying and we are now looking to install a new system. I am getting an idea from this great site on what to look for (but I will continue to take any and all suggestion) but what I am initially looking at is a 4 ton 2 stage 410 system. We have had a couple of quotes and we are now quite confused.

First, the current 3 ton system resides in a closet, and feeds attic ductwork that fees all rooms (most of the time poorly).

Due to our interest in utilizing more space in the house we have been asking and have been told to move the AC our of a closet and either into the attic or onto the roof. So, what is better? Mounting the whole system on the roof seems like a good idea cause it is easy access and not jammed into a very hot and very cramped attic, but the guy we like wants it off the roof and in the attic with little explanation of his motivation.

Second, both guys have rejected whole house fans. I have been in homes that have them and they really seem to work well. Open a back bedroom window up in the evening, and suck in the cool outside air, reducing your AC costs.

Anyway, I look forward to all the advice you can give a consumer.

Carl

[John Culpepper]

A package unit would mean some costly ductwork changes. An attic installation would probably be less expensive.

[beenthere]

An increase from 3 ton to 4 ton means some costly duct changes.

How did you come up with 4 tons. Did either do a load calc. Or did they just say they will install a 1 ton larger A/C because this one doesn't cool right.
Since you increased your insulation, doubtfull you need 4 tons.

Keep getting estimates.

[woodlandfarms]

Our ductwork is a disaster. Even as a non-pro I can tell it has seen much better days and the design is so haphazard (it is really difficult to duct our house due to the low roof line).

As for 4 tons... Even though we have insulated the house, we do not have any shade trees in the right spot. Our living room is 35X20 X 14 foot high ceiling... We have not yet re-roofed and with the cost of the AC unit we may be a couple of years off. But I am willing to re-address this issue with any potential installer (we are still interviewing but I need to get smarter than I am).

But, my big question is wether there is a difference between placing the unit (not the ducts) on the roof or in the attic.

Thanks

Carl

[WANDERSON41]

You should see that your ductwork gets sized properly.
That could have been most of your problem to begin with.
As far as the unit being in the attic or on the roof should not make too much difference as long as you are ok with the price.

[woodlandfarms]

Indeed, ductwork needs to be resized and the house re-vented. I think the contractor will need to employ a small child to reachsome of the spots.

But, what I am trying to find out is what disadvantages / advantages are there in placing the unit on the roof or in the shallow attic. Just want to make sure I put it in the best possible place with my home.

[DCSCO]

Putting a unit on the roof means penetrations for duct, electric, gas... This could put a contractor off because he has to get pricing from a roofing sub(s). Their is additional liability for leakage and architectual elements.

[bmathews]

Putting it on the roof is probably going to require an engineer to determine the way to reinforce that sucker and a framing crew to make it happen. As well as a roofer. You will probably at least quadruple the price of putting it in the attic by putting it on the roof. I wouldn't even consider putting it on the roof without consulting an engineer. A roof is designed for a certain roofing material and by simply going from shingles to tile requires added reinforcement. Imagine putting several hundred pounds located in 1 spot.

[beenthere]

An air handler in the attic is in 125+ heat. So it can lose some of its capacity.
On the roof it can also loose some of its capacity. Do you want someone walking on your roof for service and yearly maitainece.

[crmont]

Indeed, ductwork needs to be resized and the house re-vented. I think the contractor will need to employ a small child to reachsome of the spots.

But, what I am trying to find out is what disadvantages / advantages are there in placing the unit on the roof or in the shallow attic. Just want to make sure I put it in the best possible place with my home.

I vote to leave it in the closet. This way the air filter will get changed and there is no heat loss/gain at the air handler. Usually cheaper to have it serviced as well.

[classicrock4you]

As mentioned earlier, make sure that you get the right size equipment - if the contractor won't do a load calc, get one that will.

I know the attic is hot, but have you ever touched a rooftop unit on a hot day? OUCH!!!!! Go with the attic.

If you have ductwork issues, correct them now, when the attic is cooler. On a 3 ton unit, 10% leakage = 3600 btu's = 1/4 ton on cooling lost and replaced by hot untreated air - and the unit runs and runs and runs.

When you re-roof, make sure you go for high r-value insulation in attic and a light color that reflects the heat.

Sounds like you are going whole hog on renovating your home and will be there forever, so do it right.

[Dave-B]

I would suggest concidering a rooftop package with an economizer to take care of cooling the house on cool nights.
The roof top location may be better than having the service person accessing the attic (dust and insulation). You also have less likelyhood of damage to the out door section than if it is on the ground.

[oldrookie]

The design and construction of the home has created a comfort nightmare. True even comfort in this structure will take some serious mods. Go with attic air handler with service hatches. Run new supplies AND returns. Lower high ceiling to workable height that will allow for ductwork and good insulation. All this will no doubt require sheet rock tear out and installation of return chases. Expensive? Yes. The good news is that if you go high efficiency dual fuel with whole house humidifier; you will simply not believe how fast it will pay for itself AND the modifications.
Oh yeah. Forget the whole house fan. The reasons are too numerous to mention.
Get many estimates including options. Those that just want to change your units are not doing you any favors.
Just my opinion. I just believe that if you are going to fix a problem; FIX IT. Don't just put a band aid on it.