3.5 ton single stage vs 4 ton two stage

[stevek]

I'm looking to install a new central system, and amongst the many variables out there, I have one quandary.

First the background (skip right down to the question, if you'd like):

I'm in the NYC area, where humidity isn't a huge problem, (but it's an annoyance), and electricity prices are a problem.

I'm quite interested in a two stage system with humidity control for this reason.

I've had a couple of contractors come around and, they haven't done manual J yet, but they both estimate I need about 3.5 tons. One gave me quotes for a 4T single-state 15 SEER unit, and a 4T 21SEER unit (carriers), and another was pushing the "comfortmaker" at 3.5T 15SEER.

It seems comfortmaker is carrier's unbranded line, and they do offer 2 stage units, and I've looked things up, and you can get a c4a648gka with either FVM4x48 (16 SEER total) or fvm4x60 (16.5 SEER total), and these both can take humidity controls to run with slightly lower fan speeds for humidity control, etc.

The problem is, it seems that the two-stage units don't actually come in 3.5T..

My logic is, that with a two stage unit, a little oversizing isn't as bad for either humidity, or energy usage: It just means you'll be running on the low stage a bit more than the high stage.

Is that logic right?

[<kjpro]

Look with-in for my replies...

No manual J, they recieve No work!!!!!!!!!

Not exactly true...

United Technologies owns two divisions Carrier and ICP (&#39;International Comfort Products&#39; formally &#39;Inter-Cirt Products&#39;)

Under the Carrier branch falls &#39;Carrier, Bryant and Payne&#39; (they no longer use Day & Night) The Carrier products are very similair, but each brand has it&#39;s own little differences.

Under the ICP branch falls &#39;Arcoaire, Air Quest, Comfortmaker, Heil, Tempstar, KeepRite, ICP International, ICP Commercial&#39; (many other names were used previously, like Whirpool, Sears, Heil Quaker, Etc) The ICP products are practically the same from one to the other. There are very little cosmetic changes from one to the other.

You don&#39;t want to use a larger evaporator coil, if your whole concern is humidity removal. So in short, forget the FVM4X60 with the .5 higher S.E.E.R. rating. Getting the matching FVM4X48 is the better choice.

Yep...

[udarrell]

The summer design for NYC Central Park area is 89-design dry bulb,

73-design wet bulb. Madison, WI is 88-DB & 73-WB. The number of run-time hours in the NYC area is not enough to justify buying ultra high SEER rated A/C equipment. I had a graphic of run-time hours across the U.S. but misplaced it.

I would insulate and do everything possible to reduce the heat-loss & heat-gain because that will save on energy costs the year around. Proper sealing will reduce air infiltration to a minimum & thus reduce the humidity latent load to a small load effect. In my opinion, that is your best payback option.

Unless the ductwork & airflow is right you will gain nothing, & lose on payback, with ultra high efficiency high cost equipment.

- udarrell

[udarrell]

The summer design for NYC Central Park area is 89-design dry bulb,

73-design wet bulb. Madison, WI is 88-DB & 73-WB. The number of run-time hours in the NYC area is not enough to justify buying ultra high SEER rated A/C equipment. I had a graphic of run-time hours across the U.S. but misplaced it.

I would insulate and do everything possible to reduce the heat-loss & heat-gain because that will save on energy costs the year around. Proper sealing will reduce air infiltration to a minimum & thus reduce the humidity latent load to a small load effect. In my opinion, that is your best payback option.

Unless the ductwork & airflow is right you will gain nothing, & lose on payback, with ultra high efficiency high cost equipment.

Do NOT Oversize the unit! Longer run times to reduce costly cycling is paramount to efficient operation & does more toward reduction of humidity than slowing the blower speed on oversized short-cycling equipment!

Take the other gentlemen&#39;s advice & Require a manual J, D for ductwork, & S for equipment Sizing.

In your climate I would rather have the condensing unit slightly undersized than oversized!

- udarrell