Any home A/C constuction experts

[gearheads78]

I have a 1500SF home and the current A/C unit is apox 15 years old from when the home was build. The A/C works fine for the current house size.

We have plans to start adding apox 700SF to the house. Will it be better to add one big A/C system for the whole house or add a smaller second system. Looking for pros and cons for both inital cost and utility bills down the road.

[GetMore]

Some pros and cons:

Two smaller units could be "staged", where the smallest unit is used during low load, the larger unit during medium load, and both during peak load.
Or, with staged units you could use both to cool the house down just before you get home, and then the small or large one to maintain the temperature.

If you get a new unit it will likely be more efficient than your old unit, so having the proper size unit might work out to be more efficient.
Sometimes spending more now will save you later, and I think this is one of those times.

[69Bbird]

You can zone your current system into two zones this is going to be the most cost effective way. They work great too I have installed a lot of these. 15yrs is getting pretty old though you might want to think about replacement.
I'd go for one system if your going to replace it.

[amx2334]

Without seeing the plans its hard to say.will you be ducting air from the existing system to the new addition?
If you upsize the condensing unit you will need to upsize the A coil and air handling unit. 400cfm/ton is the norm.
A mini split ductless system may be an option.
http://www.minisplitproducts.com/
first cost would be lower and you don't need to disturb your existing system.

[gearheads78]

This is a very rough drawing of what the new space will look like. Door placement and swing is not decided. The existing house is down the LH wall. The only opening from the old to the new is through the dining room at the upper left.

[abadsvt]

I do HVAC for a living and there are a few options. With the addition you are only 2200sqft so you could get away with one 5ton split system. The pros to this is you will only have one system to install and purchase so you intial cost will be a little cheaper than 2 split systems. I agree with above by saying that 15yrs is a long time for a furnace and a condensor. You are wasting alot of money running that system. Back then if they said the furnace was an 80% it really was in the 60's%. So for every dollar you are only getting 60-69cents worth of heat and same thing for the condersor not being very efficient. Now regard two split systems. If you only use part of the house on a normal basis then two systems would be a good idea but if you plan on using the whole house then you probably be better off with one system. That just my opinion though. Good luck and let me know if you have any questions.

Josh

ps. They make 2 stage split systems. How they work is when the house is really cold two sets of burners turn on heating the house and after it reaches the desired temp it shuts off half of the burners so now your 5 ton system is running at around 1/2 of its energy cost. Kind of like those new cars that when on the freeway it switches to only 4 cyclinders to save on gas and when you need the power it switches back to all 8. They are a little more intially but in the long run it might be worth it.