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Am curious, was there a blower door test to determine what your expected infiltration ( Air Changes) are going to be?
Don't you need this info
My Son inherited a cubicle that had a sign without...

creqating a number of small zones is really a bad idea
the equipment doesn't like small loads and you will be tripping off on high limit in the winter and probably freezing the coil in the summer....

850 sq ft of space and 3.5 tons of overcapacity
Can you say short cycling
seems like it doesn't run long enough to remove any RH

Without a sketch, it's hard to understand what you are doing
If I understand you are reducing 4 to 2 for inlet which will increase velocity and therefore noise and pressure drop whereas ou are...

Just a guess but probably could extend 2nd floor unit to both sides of first floor for light load days for heating and cooling with extra duct and the intelligent use of closet corners to hide duct...

well insulated, Habitate, Slab on grade, no AC, seems curious you didn't consider Radiant floor with more comfort at lower air temps?

Regardless of what it is set to do HOW LONG ARE THE RUN TIMES AND HOW LONG IS IT OFF?

If you turn the unit on in May and leave it on then with extensive use a more efficient unit might make sense. Problem is as one of the others pointed out, if you have a badly designed duct system,...

Dean asked the right question this unit can have an intake as well as the exhaust( vent) so it is an important question to answeer

Sounds like you've answered your own question! Very possible that the ajoining basement stinks and your return duct either is creating a negative pressure in basement or just the jpoist space and...

You assume right!!!

Sounds like your units are in the basement and the return air is taking the path of least resistance and being sucked into basement I s that right
With Radon concerns, the last thing you want is a...

Shophound nailed the "usual suspects" but I think you have a new BOX with a deficient duct system. You are just not delivery what you need to where you need it

Our neighbors to the North have a reputation for building tight homes! Do you have an ERV? Did they do a blower door? If you have the required Insulation ( are you sure there isn't rigid...

In general, You have replaced the existing "BOX" with a (potentially) more efficient BOX but that is only a third of the SYSTEM! the other elements are the duct system and as Energy Rater will tell...

Highlight my name and use contact info. Explanation too long for back and forth posts

Let me understand this You have chilled water and the designer didn't select a coil, deep enough to remove the latent ( RH) load and you have to either pre heat or re heat the air? HMMMM...

Regardless of the units that we use, the main advantage of ductboard is the low leakage compared with standard sheet metal duct, You are sizing your duct based on your fan, so you'll need to get...

The answer to your question is: The air needs a low resistance path to get back to the unit, and undercut 3/4" clear space under the door is good for about 80 CFMs so use Darrells "jump duct" advice...

Hey Mr Bill, long time no hear, I sometimes go into "remission" with posts but to answer your question How about if the unit was horizontal, you know those typical "economy" jobs with just a...

You may first want to ask yourself, Why is this unit removing thrheat but not the humidity? Is the charge right? probably or you wouldn't cool Is the airhandler set at 350 CFMs per ton for that...

Darrell, there are a couple of "old BEST PRACTICES" that are not really based in fact or engineering, like within 6 or 12 inches of the end of a duct OR as you mentioned: the endcap OR the top of...

If the customer did a similar thing to you as an auto mechanic, how would you feel about the situation?

If the duct ( other than you concerns about too big) is sound and will carry the air THEN BIGGER IS BETTER!!!!

Bigger duct means lower velocity, which means less fan horse power.

Same...

Seems like your main concern is winter (you probably don't see much summer load) and therefore you may want to check indoor pressure WRT (with reference to) the outside, keeping inside slightly...

You do understand, that unless the intake of that exhaust is very close to the source of the soldering fumes, that it is going to have very little effect on the air quality!

Industrial exhaust...

Great answer! every time you "start-up" the unit and reduce the indoor temp and RH , there is the possibility and in Miami, the probability of sweating duct!
Thing is, bare duct is going to be...

I agree with beenthere, it's all about usuage,recovery rate/ storage with the complication of a better rate for off-peak. Although I don't see where on peak usuage would trip, or get close to 80%...

The added 8" duct will reduce the overall resistance of t6he duct system and therefore you should get more CFMs with the lower Available Static Pressure
Which enc you put the exhaust fan will...

How about just an outside air louver, low and through the wall to equalize the pressure diff? if there isn't a concern about freezing ( you said seasonal) then you don't even need a damper to seal...

You're right George, too many contractors go broke because they didn't know their cost.
But you'll agree (I believe) that one of those cost is the Sales cost of the SG&A and just as important HOW...

Clearly you are "fiber-phobic" and therefore Dan's reference below"



Is really timely! All concerns about "fibers in the airstream has been put aside when the Govt accepted ( 9 years later) ...

Point is, So I would harbor any bad felings for what you didn't know and therefore didn't tell them and then they didn't know either!

I share Dan's concerns PLUS I would like to mention the much higher First Cost and the Much higher Repair cost and limited number of people who can service the more complicated unit
The owning cost...

NO you are not nitpicking, but you are showing off! Clearly you know the proper procedures, so I wonder why you even posted this?

You asked the question, I thought I would say out loud what I...

Let's see: You came recommended by your mutual friend/ acquaintance, the contractor got the lead with no sales marketing cost, you were described as a reasonable / low maintenance,/ business owner...

Teddy bear, it's my understanding that you need organic material (dirt) AND LIQUID WATER to row "bugs"
After all the place where the highest RH found is at the discharge of the AC unit

Does that...

Do you insulate then cut and mount take offs? Sounds better than next Mount take offs then insulate?

Do you double insulate attic ducts? Bad idea to have a double vapor barrier that would...

You Guys clearly got the skinney on this poster, I give up and will go quietly

Thing is the answer to his question is of no value to a DIY except to make clear that the "civilian" is not going to...

Yes, increasing the motor speed will require more energy, but a small amount compared with running the unit longer to get the troubled area to temp while over-cooling the other spaces
Increase...

I think you answered your own question

Point taken,
Of course if this tech is the kind of person who takes pride and possession of the work he does, than that could explain the "my" part

Don't you agree that we didn't and couldn't...

Clearly you are not from US
Ductboard is tested to 2.5 times listed velocity and no erosion, so at 2500 FPM which is 3X what you would normally see in typical residential designs, velocity is not...

beshvac is right! you don't have a sealed crawl space, you have an indoor swimming pool!!!!!

If cost is a factor, you may want to insist that the w3ell meaning HVAC Contractor who didn't...

I think you all are misunderstanding this guy, who is most likely in the biz, not one of the approved or a DIY who has a non US piece of equipment and was looking for an answer that has nothing to...

I thought the big problem was not having enough capacity for the connected load? Wonder why you couldn't just use a smaller nozel if you think the "overfire" was too high?

I think the Non Chemical / JM reference was made to do exactly what has happened....You asked the question Chemical what?
I think JM is calling your attention to the potentially bad fire...

The connector vs duct issue is a matter of the flex passing 1 or 2 additional tests like flame penetration (I think) almost all the manufacturers have gone to the DUCT classification but consider the...

George has it right! The return has top be large enough to provide a low resistance path back to the unit And a brilliantly placed return grill (location( will not make up for not enough or properly...

If Nat Gas is aviliable and the Utility doesn't discount Heat Pump use any longer than 90% Gas Furnace best bet. You can hedge your bet somewat by installing a heat pump split instead of just a...