Our house is a 1995 tri-level home in Phoenix. It is 2196 square feet with an existing 5 ton single Trane unit. Two of the three bedrooms upstairs are 6+ degrees warmer than the rest of the house and they are south facing. Those rooms have new energy efficient windows - the rest of the house has 1995 dual panes. We have R30 insulation in the attic that was just blown in a few months ago. We have had several bids and have received very different advice. Each contractor states we should get a unit with variable speed. One contractor states the warm rooms have the registers too close to the door of the room and we should relocate them father away and install a 16 seer two stage Trane unit. The second contractor states we should add a second return in the warmer bedroom and install a 14 Seer Night and Day unit. The third contractor believes the American Standard Platinum 16 Seer two stage unit should equal out the heat issue and if not, then we address returns/moving registers. All of them are stating a 5 ton unit should be used again. All of them agree that the 18" return duct size is adequate and can be left as is. Only the one company suggests an additional 12" return in the warmer room to give additional air flow.
After reading many pages of this website forum I am really confused. It seems as though a two stage unit works best in humid areas and not in areas like mine with an average 5% humidity. Also it seems that 5 tons may be too large for the size home that I have at 2196 sq ft. No one did a load calculation (that I have been made aware of) so I will need to ask about that when I touch base next week. My main questions are:
Is 5 tons too much for a tri-level of my size?
Is a 2 stage unit a good idea for a hot, dry climate?
Should there be more return air than an 18" duct can provide?
We are leaning toward the American Standard, but I would appreciate any insight that anyone here would like to share. Thanks in advance for your time.
First thing has any of the contractors performed a load cal on the home? If I am reading your post right you have 3 levels with one system is that correct?
If so has anyone of the contractors talked to you about zoning or adding add. Unit/units to the home for upstairs? 1 system will have a hard time to keep all the levels in the home comfortable unless zoning is a option or more units installed for each floor (properly sized for the load) of each floor.
How big is each floor of the tri level home? I am gathering from your post (my opion) that the existing unit and the new one you will be installing is sized by square footage plus the tri level design which may or may not be correct depends on the home.
Please post back what all the contractors said about the sizing of the equipment and the supply and returns. A (5) ton system requires a lot of supply and return. If you do only have 1 system again it will be hard to keep the upstairs of the home comfortable unless zoning can be done. There are many options available to combat your situation, the treat is to find the right one and the contractor that will install it right!
Our house is a 1995 tri-level home in Phoenix. It is 2196 square feet with an existing 5 ton single Trane unit. Two of the three bedrooms upstairs are 6+ degrees warmer than the rest of the house and they are south facing. Those rooms have new energy efficient windows - the rest of the house has 1995 dual panes. We have R30 insulation in the attic that was just blown in a few months ago.
We have had several bids and have received very different advice. Each contractor states we should get a unit with variable speed.
One contractor states the warm rooms have the registers too close to the door of the room and we should relocate them father away and install a 16 seer two stage Trane unit.
All of them are stating a 5 ton unit should be used again.
All of them agree that the 18" return duct size is adequate and can be left as is.
Only the one company suggests an additional 12" return in the warmer room to give additional air flow.
It seems as though a two stage unit works best in humid areas and not in areas like mine with an average 5% humidity.
Also it seems that 5 tons may be too large for the size home that I have at 2196 sq ft.
No one did a load calculation (that I have been made aware of) so I will need to ask about that when I touch base next week. My main questions are:
Is 5 tons too much for a tri-level of my size?
Is a 2 stage unit a good idea for a hot, dry climate?
Should there be more return air than an 18" duct can provide?
We are leaning toward the American Standard, but I would appreciate any insight that anyone here would like to share. Thanks in advance for your time.
5 ton is likely necessary in Phoenix.
Duct system needs to be designed for 2,200 CFM using ACCA Manual D.
TWO 18" diameter flexible duct ARE REQUIRED for the Return Air.
I can imagine a lot of duct work modifications may be needed to reduce the temperature differences.
A goal of 3'F difference might be achievable in a more economical manner with less retrofits.
How does your monthly electric bill correlate with Cooling Degree Days?
Month starting CDD
11/1/2011 _____ 50
12/1/2011 ______ 5
1/1/2012 ______ 27
2/1/2012 ______ 34
3/1/2012 _____ 126
4/1/2012 _____ 293
5/1/2012 _____ 564
6/1/2012 _____ 824
7/1/2012 _____ 830
8/1/2012 _____ 888
9/1/2012 _____ 643
10/1/2012 ____ 368
___________ 4,652
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
4 TONS Might BE Able to be used for a WELL PERFORMING SYSTEM.
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
With a single 18" return you aren't GETTING 5 tons delivered capacity. I would investigate splitting the load between 2 units, one for upstairs, one for the other 2 levels. One system for 3 floors is just begging for temperatures to be uneven. 2 basic 14 SEER units may may be the way to go vs. single 16 SEER system with VS air handler. Energy bills will likely be LOWER with 2 smaller systems vs 1 large system.
I would split the house in 2 zones and use 2 smaller systems if possible , if you stick with one system it needs a zoning system and a 2 speed unit ,and a 18 inch duct don't cut it for 5 tons ,you need to add at least a 14 inch to it or you varible speed motor won't last and will suck the electricity trying to move 2000 cfm through 18 inch flex
It takes a Lot of room to zone a 5 Ton unit correctly especially with 3 zones! Like has been said one 18" return on 5 Ton is undersized, so adding returns in mandatory. VS blowers are nice but for correct zoning must use modulating dampers i.e. NO bypass, which ups the price. I may catch heat for this but if you have only had issues with 2 rooms the way your home is currently, you may be able to get by with minimal modifications, like putting in more returns and adjusting airflow so the 2 bedrooms are more comfortable. Depending on your finances you can get creative and go with two systems and zoning one to get the best comfort and longer lasting equipment. But you may be able to get by with a simple change out with ducting mods such as more return and better supply to uncomfortable rooms. If thoes are the only 2 rooms that have been uncomfortable with your layout you are lucky.
Thank you to everyone for their replies. At this time, we do not have the funds to redo the system with two smaller units. Due to our limited budget, we need to work with things pretty much as they are. I will call the contractor with the American Standard and mention that we would like to have either a larger return on the house or additional returns added in the warmer bedrooms. I appreciate everyone taking their time to write back with ideas and suggestions. Happy Thanksgiving to you all!
Being that the return air duct appears undersized, increasing the amount of return available to the blower may help the rooms that are too warm (I assume since Phoenix is the location we're talking about cooling issues, not heating) be more comfortable. Only caveat is if the ducts that supply these rooms are sized correctly, or if they are it's then a matter of were they installed with minimal bending, kinking, etc., all of which can reduce airflow.
I'm not buying "the supply is too close to the door" thing you were told by somebody. That would only be a problem with a really crappy supply grill that caused all the air to drop right by the door and then get sucked out into the hallway return. And if that's the case, get a better supply grill. Builders often install the cheapest, most air restrictive models on the market, which also have poor air throw patterns. Don't blame the location right off. It's actually better to throw the air into the room, toward the outside walls, than to throw it back into the room from near the outside walls.
Electricity makes refrigeration happen.
Refrigeration makes the HVAC psychrometric process happen.
HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.
My E$timating indicate$
_ _ 2 + 2 = 4.6 _ _ for two HVAC systems.
However, performance and Comfort may be _Worth It_ in several situations, ESPECIALLY, TRI-LEVELS.
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
Initial Cost versus Life Cost$
_ Gaining __ Perspective + Comfort
Another evaluation factor has intangible attributes: the perception, or “I want it,” factor. This does not have a numerical value or formula but must somehow be taken into consideration when evaluating an investment.
If the world of consultants were polled today, it is reasonable to expect that many of us have introduced additional systems that incorporate equipment or design features to get that last LEED point at the owner’s request, and not because it made financial sense. LEED certification can increase an asset’s value and attract tenants, so extra LEED points may make financial sense outside of an engineering perspective.
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
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