sounds like a poorly balanced duct system and maybe insulation issues too. Try closing the registers in the main areas a little. Also, the warm northwest side of the house, shade the exterior wall to minimize it getting heat-soaked towards the end of the day. Plantings? Large arbor? I can't see why a 2300 sq ft house would need 2 systems. Obviously with outside walls, the bedrooms get more heat load...they just need more cooling than the interior areas.

could try to add more returns to the area thats the hottest in the house.

Or depending on ducting add automated dampers and zone controllers/zone thermostats. Really depends on how the ducting was designed.

I can't see why a 2300 sq ft house would need 2 systems.

my ~2400 sq ft home has 2 systems. we have a 3.5 ton Trane up front and a 3 ton Rheem for the bedrooms. if i had been REALLY thinking about it when we replaced the front unit last year, i would have gone with a single unit for both.

but in reality the system works great. we prefer to sleep with the room cold. so at night we cool the bedrooms to 70, while the front system shuts back to 79. no sense cooling an area no one is in.

oh, and it was NICE a couple years ago when the squirrel cage fan in the rear unit crapped out and we still ahd good air up front. we slept on the hide-a-bed for a couple days, but we slept cool. and when the front unit was replaced and they had issues we just stayed in teh bedrooms. drawback is, it cost 2x the electric to run them both!

Actually it's not 2x the electric to run it.

By splitting the loads, youÂre reducing the current use at both compressors, blower motors versus one unit combined use. And the systems are more apt to run less reacting to the different areas rather than overcooling areas to keep the stat area at its set point.

Besides that you donÂt have a choice as, you canÂt get a 6.5 ton residential single phase condenser.
I once saw a 6 ton drive furnace in a house with 2-3ton coils and condensers staged, but still had common ductwork.

Well I think it is wasting energy to keep the main area of the house as cool as I prefer it at night in the bedroom no matter what. Both my previous houses that were two system were 2400 sq ft and it was very useful and spent way less energy as we let the main area be higher at night. Not sure about closing the registers in the main area as it is comfortable as is during the day and too tall ceiling to open and close on a regular basis.

Actually the northwest bedroom is the least warm one due to being shaded by a porch, so no need to do anything there.

So what would adding returns from the bedrooms accomplish? I'm not seeing how that would make those rooms more comfortable other than drawing some warm air out of there which I don't think is an issue as we keep the doors open at night, but if they don't get cooler not sure how it helps. Could somebody please explain how it would help.

heimert - we have the fairly standard use in our area flexible ducts, but if re-designing the duct system would be less than adding another system and downsize the current one (we have lots of height in attic) and would be more energy efficient I would like something like that. Where can I find more info on it?

1) Adding returns would pull warm air out and the cool air in other parts of the house would then filter into the bedrooms to take its place.

2) You'd have to consult with an HVAC person. I have no idea of cost, but I do know (because we were thinking of doing it) that one can use multiple stats to control dampers that create more or less flow to given rooms to address just the problem you're having.

heimert thanks. I doubt the local HVAC has any experience in that in our tiny litte town, but I'll have to check.

for returns, I see how this could help in bringing cool air from other areas. Could we close the doors then?

6.5 tons of cooling in a newly built 2300 sq ft house (should be up to new energy codes)seems like way too much....My 2000 sq ft has 3.5 tons.

gary, the 6.5 tons was in reference to MY 30 year old house. honestly the 3 ton for the rear is probably over sized, heck the bedrooms make up maybe 1000 sq ft total including the hall and 2 baths. and i know the 3.5 is 1/2 ton over. the front 13-1400 sq ft of my house has 4(actually 5 if you count the french door as 2 doors) exterior steel NON-insulated doors with single pane windows, and 8 36"x72" OR LARGER windows which are also single pane metal frame. guess what the next replacement will be! 7 of the windows and 2 of the doors face south or southwest, so they pull in heat.

oh, it has already started to cool off for today, down to 95 with 47% humidity heat index is 104. was up a hair over 97 with a heat index of well over 105. around here you almost can't have too much cooling. i spec'ed the front unit to bring the house to 70 even with 105 outdoor temps. sure blows cold about dark, but it keeps it comfortable during the hottest part of the day.

6.5 tons may not be too much depending on where you live.
Some areas have a design temp of 30 degrees plus and must account for exposure, higher sensible loads (heat) and latent loads (moisture) than others.

Normally the range is 15 to 25 Btu's per square foot depending on construction type, windows, infiltration, climate and others.

The original poster has 2300 sq ft but never mentions what size AC.

David & Kaisey has 6.5 tons in 2400 sq ft in TX. Seems like a lot yet don't know their situation.

One downfall to oversized units is limited run time causing reduced air changes in areas during operation resulting in mixed temps. Of course the other major pitfall is reduced humidity removal.

I have 9 tons with 4600 sq ft. (23.5 Btu's per sq ft in Houston). Having had some hot and humid days last year, ours couldn't have been any smaller to obtain comfortable temps of 72-74 in our house.

lyfia,

If you take a look at the ductwork distribution system, you will probably notice that the rooms you are having problems with have flexible duct and your main areas are probably "Hard ducted". Flex is notorious for creating resistance which can not be overcome by the fan. If you do an experiment by replacing one flex run with hard ducting of the same size you will notice a dramatic difference. Your problem is most likely "Underventilation" caused by excessive resistance in the flex duct. Make sure the dampers are fully open in the bedrooms too. In commercial work "Flex" is limited to 5 or 6 feet.

Hope that helps,

Dan Martyn

Dan Martyn, thanks for your response. All rooms have flexible ducting - including main areas. Standard cheapo builder thing to do in TX.

All dampers are fully open.

Also the master bedroom has the shortest run as far as the ducts go except for the breakfast nook.