It was suggested on another website that I pose this scenario here......
That's what our HVAC guy said was necessary. I'm building a pretty big house and was very shocked at the amount of ac we're having to put in. 6 zones--19 tons--yikes. I guess there is actually some overage due to the # of tons available on different units.
I walked the house with the HVAC man yesterday and he analyzed and marked where all the ducts would go. The zoning that he did seems very logical, however I don't know diddly about this!
At the beginning of our meeting, I asked him if he had done load calculations for the system. He said that he had. When I was shocked at the amount, he mentioned that 1 ton would handle up to 400 SF.
We are upgrading from Trane 12 seer units to Trane 19 seer units........I think those are the numbers.
I was just shocked. Does the ratio sound right?
Help!!! I'm about to spend a load of cash on this system and I guess I need some confirmation that it's a good thing to do.
19 tons? At that point, I'd suggest finding a contractor who does mostly commercial work.
How big is a pretty big house?
My math comes out to 16 tons, but maybe thats not a concern. Not trying to be picky,just saying. Are you having on system installed or several systems? Unless you have poor insulation or alot of large glass exposure I think you can get that capacity requirement down. Doesn't hurt to get a 2nd opinion. You know, a second load calc done.
This was the preliminary zoning breakdown, but I know it had to change a bit.....there is one room that is attached to the detached garage (clear as mud?) that they originally called for a mitsubishi something. I didn't want that, so they are putting it on it's own regular unit.
Zone 1 - 1532 SF - Trane 4 ton
Zone 2 - 1100 SF - Trane 3 ton
Zone 3 - 1400 SF - Trane 4 ton
Zone 4 - 1578 SF - Trane 4 ton
Zone 5 - 885 SF - Trane 2.5 ton
That totals 17.5 tons.....we might actually be at 20 tons if the unit for that other room is 2.5! I can't remember what he said about the smallest size.....
Is that correct? I'm getting a system installed in my house and the contractors are putting in a 4 or 5 ton unit to service 3100 sf. Where do you live, Death Valley?
Yeah PowerG--I'm clueless here. LOL, no I don't live in Death Valley. I'm in the Dallas area and although it gets pretty danged hot here, it probably doesn't compare.
[Edited by keriwest on 05-18-2005 at 08:07 PM]
I have seen residential cooling loads that high however it is in a humid tropical environment with lots of glass looking out at the Caribbean.
The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.
Get written proof of "Manual J" cooling load.
It sounds way over sized if it is new construction.
I would freak if I needed a 8-ton unit to heat/cool my house! I wonder what you will require if you live in a house (6400 sf) with almost all windows in Death Valley?
1 ton per 400 square feet...a rule of thumb sizing method that can bring about big problems!
Case in point...my house is 1500 square feet and has a 3.5 ton system in it. Going by the rule of thumb method it should actually have a 3.75 ton, but since nobody makes one that size, most any installer would round up to 4 tons.
However, I ran HVAC-Calc on my home, accounting for recent insulation upgrades and planned window upgrades. End result? I'm a ton oversized with my existing equipment.
And yes, the system as it is truly is too big for this house. I've already slowed the blower speed and tweaked the charge...better but not great. Right now with outdoor temps in the high eighties the system runs five minutes tops before cutting off. Comes on again about 10-15 minutes later. Runs five minutes and it's off again. Not the best recipe for good dehumidification.
Suffice it to say in your case I would not settle for ANYTHING less than a properly executed Manual J heat load calculation. Oversized equipment in North Texas, where I also live, is bad news. Especially in new construction that's tighter than my old Fox & Jacobs job. Our humidity levels are not as severe as Houston's but with oversized equipment, you may actually rethink that!
Building Physics Rule #1: Hot flows to cold.
Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.
O.K. 4 tons for 1532 square feet? All I can say is this... I live in Northern Indiana. We do not have near the load of Arizona or Houston ect... but it's not uncommon to see the 90's in July and August. I live in 1632 square feet on a concrete slab. My air ducts are buried in the concrete. 2x4 wood frame construction with batted exterior walls. I have a 2.5 ton A/C and it works great. If it's hot and you have alot of windows, maybe he's on target. But I must admit that seems like a lot of air.