help me size central air for my house, R-22/410?

[1 FMF]

going to be installing central air in my house,
colonial style, 2 floor. I am only doing upper floor, there's no reasonable way to run ducting to the main ground floor and I am not sacrificing any closet space. Have other plans for ground floor anyway.
I'm hoping to get some educated advice here to back up what I think I need and also what the installer who will be supplying me the equipment thinks I need.

The upstairs is just 3 rooms, the master bdrm is I think 143" x 212" if I remember, and the other 2 rooms are slightly smaller, and there are same sized bathrooms- one in upstairs hallway and off master bdrm. I believe I calculated square footage of upstairs including small hallway area to be 700-750 sqf. And it's 8' ceilings everywhere. My downstairs (which i am not doing at this point) is roughly 800 sqf, that whole area measures 33' x 25' if I measure the whole inside as a rectangle.

I also had the house sided last fall, it's the 1/2" styrofoam over existing wood shingles with aluminum siding. Also have brand new windows at the same time, they're certainteed double pain glass with gas layer in between, argon I believe, and with the reflective heat coating on the glass. Basically about the best energy efficient window you can get. The attic is also fully insulated- the floor above the upstairs ceiling. Along with insulation in all the exterior walls which I can confirm from having done the windows.

So, just doing the upstairs for AC what tonnage system should I go with?

what are you're thoughts on R-22 vs R-410? I already got a price for the R-22 system, and was told R-410 would only be couple hundred more. I know they market R-410 as being more efficient, but I don't see how when the system lo/hi pressure is 3x that of r22?

what's the deal with oversizing vs undersizing AC systems?

 

[simple_gifts]

DO NOT oversize it; all you will get is cold wet air.

 

[Bill in Utah]

Originally Posted By: simple_gifts
DO NOT oversize it; all you will get is cold wet air.


Agree.

Also a lot of temp swings.

I'd recommend R-410 since that freon is going to be more avail now and in the future (unless the EPA / greenies do something) R22 is more expensive I've been told.

My Dad and I built the same house 10 years ago. I put in a 3.5 ton unit and he put in a 4 ton.

My electric bills are lower and my home stays cooler longer than his. His unit starts up and runs shorter and shuts off. It just cycles more on and off for temp swings.

Mine runs longer but since its slower to cool, it actually is cooler overall. The cost to operate my A/c is about $30 cheaper even though I keep the house cooler (he is @ 78 and I am at 76) overall.

I do wish I had a separate A/C system in my upstairs since we have a 6 degree difference between it and the bottom stories (I have a 4 level home) and I try to sleep upstairs.

If I keep the fan on all the time, the temp diff from upstairs to down stairs is less than 4 degrees. The cost to leave the fan on all the time works out to $5-8 bucks more a month.

Same problem with my dads home too.

This summer, the basement will be where I sleep..

Take care, bill

 

[TooManyWheels]

Either do the research on how to do the sizing calculation (called a "Manual J") yourself (it's not difficult), or hire a contractor who knows what it is and will show you the calculations. Many contractors use rules of thumb, but the contractors who take pride actually calculate. And as said above, if you are off, undersize is better than oversize.

 

[Brett Miller]

Take a hard look at the Carrier Infinity system with zoning. There is not a better system on the market.

 

[1 FMF]

well i am not a big fan of carrier, i appreciate the help but i work for utc and get can get a carrier rebate. they had come to work for earth day i think, advertising ac systems and i asked about purchasing one and they were complete dikheads, so they can go blow now. plus i have been told my more than a few that carrier parts and service are terrible and they are overpriced because of the carrier name. Also, I am not doing zoning because of the style of my house, this is strictly an upstairs system that will be doing 3 bedrooms, 2 small baths, and the air will flow downstairs into the living room. I am counting on the airflow into downstairs, just haven't played with the numbers in the cooling calculating to know whether I should go 1.5 or 2 ton; i am planning on the main return in the upstairs hallway which should pull a decent amount of air from downstairs.

R-22 30lb cylinder is $190 and R-410a 25lb cylinder is $220 at r22.com.
So r-22 is not more expensive, if you're being told that you are being lied to, which is why i am doing this research.


can somebody hook me up with a manual J? I don't want to pay for it.

 

[PCT1981]

Keep in mind. The production of R22 equipment will be banned starting in 2010. You will still be able to get parts and refrigerant. The production of R22 refrigerant will slowly be phased out until 2020. Why install a soon to be obsolete piece of equipment? Go with the R410a system. I'm not a fan of Carrier either, you're paying for the name. Plenty of other manufacturers with good quality equipment.

 

[oilyriser]

Measure window area to calculate solar gain. There should be a formula in a book somewhere for your latitude. If you have no unshaded south facing or west facing windows, you won't need as much a/c.

 

[Al]

Your best bet is to install 3 window units by cutting out in your walls. That's the smart efficient way to go. Please consider it. If possible put them on a North/East wall.

You would need no more than a 6000 BTU unit/room. Smaller is better. The whole job would cost you way less then installing a split system and if a unit goes bad..pitch it.

 

[alreadygone]

Originally Posted By: Al
Your best bet is to install 3 window units by cutting out in your walls. That's the smart efficient way to go. Please consider it. If possible put them on a North/East wall.

You would need no more than a 6000 BTU unit/room. Smaller is better. The whole job would cost you way less then installing a split system and if a unit goes bad..pitch it.


Round here, I thought ya only done that if ya live in a 10+ year old house trailor!

Bob

 

[Steve S]

I see there is some knowledge here about a/c .can you run a swamp cooler through ducting like a HVAC unit? I have a 2400 sqft ranch style house that has 3 HVAC units that divides the house in thirds. The center unit is never used .I have a window swamp cooler that cools the section of the house very well. It would be nice it the swamp cooler was out of the way. Sorry to hijack the thread .

 

[Steve S]

Originally Posted By: alreadygone
Originally Posted By: Al
Your best bet is to install 3 window units by cutting out in your walls. That's the smart efficient way to go. Please consider it. If possible put them on a North/East wall.

You would need no more than a 6000 BTU unit/room. Smaller is better. The whole job would cost you way less then installing a split system and if a unit goes bad..pitch it.


Round here, I thought ya only done that if ya live in a 10+ year old house trailor!

Bob
That would save lots of $$$ in labor and material and in the hvac unit. I belive the cost of energy will not get cheaper .I am into lowering the cost of living as possible which will increast the standard of life as possible.

 

[TooManyWheels]

I disparaged rules of thumb in my earlier post, but you should know that just applying a common rule of thumb sizing of 750 sq. ft per ton against your estimated area means that you would need around a 1 ton unit. To be truthful, the 750 number is probably high, with your insulation and climate the number is probably lower, meaning you would need less than a ton.

The problem is that, to my knowledge, the smallest central units normally available are around 1.5-2 tons, although you may be able to find something smaller in the "high velocity" systems, or the systems where the inside coil is mounted as an appliance in the room, like you see in hotels. Unfortunately I don't remember the common name or brands for these at the moment, but at least you can start thinking in different directions.

 

[Al]

Originally Posted By: Steve S

Bob
That would save lots of $$$ in labor and material and in the hvac unit. I belive the cost of energy will not get cheaper .I am into lowering the cost of living as possible which will increast the standard of life as possible. [/quote]
It will save a lot of energy believe me. You only cool the rooms you need to and to the degree you need to. We have a 5000 Btu unit in our bedroom that draws 4.64 amps (around 500 watts, we also have a 6200 Btu unit which is around 600 watts in our 18 x 20 addition with a 15 ft ceiling. Do the math. Its the cheapest way to go installation and operation wise.

 

[brianl703]

Originally Posted By: TooManyWheels
or the systems where the inside coil is mounted as an appliance in the room


Ductless mini-split systems

 

[XS650]

You will have a lot of cool air sliding down your stairs being replaced by hot air from the ground floor.

You will need a bigger unit than youi= normally would for 750 sq ft with your construction and weather conditions. Unless you shut off the upstairs when you are cooling it.

 

[TooManyWheels]

Originally Posted By: brianl703

Ductless mini-split systems


That's it! You're The Man!

 

[Al]

Originally Posted By: XS650
You will have a lot of cool air sliding down your stairs being replaced by hot air from the ground floor.


And chances there will be a single return duct in the hall (bedroom doors cut off at bottom for return air) The upstairs return will have using as a lot of its return hot air from downstairs. That will require some extra cooling.