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Central heat and Air units / choosing one


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14 replies to this topic

#1 OFFLINE   jimmie57

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Posted 30 October 2013 - 05:24 AM

I am not an Heat and AC man.

 

I just went thru the process of choosing a new system to replace my 16 year old broken unit.

I learned that they have 2  stage compressors that use a lot less electricity.

The condensers are much bigger and have lots more heat transfer coils than the older ones. Along with that my old unit used 7-1/2 lbs of Freon and this new one uses 14 lbs.

The furnace ( gas ) has a 2 speed heater in it.

The blower has a variable speed motor.

 

The best way for most anyone to understand what this does for you is to relate it to driving in the city with stop lights.

The light turns green and you slowly accelerate to the speed limit and when you see you need to stop you take your foot off the gas and slow down to a stop. The blower motor and compressor / furnace mimic this same thing.

When the unit turns on you basically do not even know it. There is no hit with the start like the units that do not have these features. The lights do not flicker when it starts.

 

Another benefit of the variable speed operation is that when the fan motor is running slower the air is moving slower over the cooling coils. This allows more moisture to be taken out of the air.

 

Another benefit of having the 2 stage system is you can put in a larger unit. My house was between a 4 ton and 5 ton unit with the calculations. I chose the 5 ton. When it is not needed the compressor runs at 67% of it's capability ( 3.35 tons ) and if needed it can kick it up to the full output and be a 5 ton unit. The furnace is the same way. This is done automatically.

 

On top of all of this being quieter it also saves you money on your utility bills.

 

There are also units that have 2 separate compressors, communicate with data to the thermostat as to how it is doing, program your thermostat from the internet, etc. I chose not to get that for my use. It is quite a bit more expensive.

 

Bottom line. Do lots of research before you buy your next unit. A few hours of research might result in many years of pleasure from your choice. Compare the brands and the features of each of the brands and models that each brand has to offer.

Get several bids. My bids for what I needed / wanted varied from $10,000 to $15,000. Check out the dealers for feedback and the Better Business Bureau. In my case the $10,000 bidder was the best in the BBB, had the most professional quote ( listed every thing line by line with part numbers, not a description ) and had the best feed back between the 3 of the bidders. The brand is the same brand I am replacing. From what I have seen so far of their work on my unit it is first class.

 

A word of caution. The SEER ratings say "up to" XX.x. The smallest matched unit they have is capable of that number. As you step up in size that number drops. My unit's literature said up to 17.2. My 5 ton unit says up to 15.2. It is only that if all the pieces are matched.

 

Hope this might help someone with their choice when they have to replace as I am doing as I type this.

They started my install yesterday and will finish it this morning.

 

Edit / Add: They finished my unit today. I found out when he explained the thermostat that I can set the AC temp, Set the Heating Temp and then choose Auto for the mode of operation and it will switch to whichever is need for the current temperature.

Also found out that the unit I bought has a Rebate. Mercy ! Cool and quiet and a Rebate .


Edited by jimmie57, 31 October 2013 - 08:43 AM.

DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
HR24-100 Component cables to 46" Samsung LCD & Optical Cable to Yamaha AVR, H21-200 HDMI to Yamaha AVR & HDMI to 52" Mitsubishi LCD


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#2 OFFLINE   trh

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Posted 30 October 2013 - 06:27 AM

What part if the country do you live and where are your ducts located?

#3 OFFLINE   jimmie57

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Posted 30 October 2013 - 06:52 AM

Location is under my avatar. 10 miles from the Gulf of Mexico. 35 miles south of Houston,TX.

My house is a single story and the furnace and blower and all duct work is in the attic.


Edited by jimmie57, 30 October 2013 - 06:53 AM.

DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
HR24-100 Component cables to 46" Samsung LCD & Optical Cable to Yamaha AVR, H21-200 HDMI to Yamaha AVR & HDMI to 52" Mitsubishi LCD


#4 OFFLINE   dpeters11

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Posted 30 October 2013 - 07:52 AM

I wish I was able to go variable, but after getting word in February that my furnace could not be turned on and was red tagged, I got what I was able to at the time. Of course even that was an upgrade.



#5 OFFLINE   trh

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Posted 30 October 2013 - 06:57 PM

Location is under my avatar. 10 miles from the Gulf of Mexico. 35 miles south of Houston,TX.

My house is a single story and the furnace and blower and all duct work is in the attic.

I was viewing your post from my phone and it doesn't show your location. Sorry.

 

You're in IECC Climate Zone 2 - a hot & humid zone.  Same as me.

hygrothermal_regions_web.jpg

 

You said by having a 2-stage unit, you could select a larger unit.  In the AC world, larger is not better. Right-sized is what you need.  If the unit it too big, it short-cycles (it runs less because the larger size unit takes less time to cool the house). That creates more wear-and-tear on the unit and since it isn't running as long, it doesn't dehumidify as well. 

 

I am not an Heat and AC man.

 

The best way for most anyone to understand what this does for you is to relate it to driving in the city with stop lights.

The light turns green and you slowly accelerate to the speed limit and when you see you need to stop you take your foot off the gas and slow down to a stop. The blower motor and compressor / furnace mimic this same thing.

When the unit turns on you basically do not even know it. There is no hit with the start like the units that do not have these features. The lights do not flicker when it starts.

 

Another benefit of the variable speed operation is that when the fan motor is running slower the air is moving slower over the cooling coils. This allows more moisture to be taken out of the air.

 

Another benefit of having the 2 stage system is you can put in a larger unit. My house was between a 4 ton and 5 ton unit with the calculations. I chose the 5 ton. When it is not needed the compressor runs at 70% of it's capability ( 3.5 tons ) and if needed it can kick it up to the full speed and be a 5 ton unit. The furnace is the same way. This is done automatically.

 

On top of all of this being quieter it also saves you money on your utility bills.


A word of caution. The SEER ratings say "up to" XX.x. The smallest matched unit they have is capable of that number. As you step up in size that number drops. My unit's literature said up to 17.2. My 5 ton unit says up to 15.2. It is only that if all the pieces are matched.

 

 

My recommendation is get a reputable organization to conduct an energy audit/calculation on your house.  It should be done using ACCA Manual J (Air Conditioning Contractors of America - Residential Load Calculation). It is the only procedure in the US recognized by ANSI (and is required for ENERGY STAR homes). Most HVAC contractors use it, as do energy utilities and a number of third party companies. 

 

Read and make sure you understand the report.  Some contractors like to increase the number of occupants or windows in a house to increase the cooling load. Or if they use "worst case" on their calculation, it maybe increasing your AC size by 1/2 ton.

 

To check the tested SEER rating of your combined units, go to http://www.ahridirec...pages/home.aspx (don't forget to enter the security code in the bottom right corner).  I have a 15 SEER compressor and a 13 SEER rated AHU. But the AHRI tested value for the two units combined is 15 SEER.  Note: AHRI results were used up until a few years ago. Then someone realized that the units were tested in one location and the results will vary based on installation location. So now an ACCA Manual S (System selection) is required by code.

 

But for anyone replacing a unit, keep in mind that if you had an X ton unit in your house and it was cooling it, there is no need to increase the size of your unit.  Increase SEER is good up to a point. But eventually you run into the 'law of diminishing returns."



#6 OFFLINE   dpeters11

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Posted 30 October 2013 - 07:12 PM

Wow, who do I tell to have them correct the errors for Cincinnati?



#7 OFFLINE   jimmie57

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Posted 31 October 2013 - 04:57 AM

By choosing the 5 ton 2  stage compressor condenser unit it effectively runs at 3.75 tons unless it can not keep the house set to what the thermostat is set for. This is just a hair less than the old 4 ton it replaced. When it can not keep up it then runs at max output of 5 tons and gets the job done.

In the summer when it is 95 ( we had some days it was over 100° last summer ) or above my temperature would creep up to 80 in the hot evenings. I have a physically handicapped son and that is not acceptable for me.

 

The reverse was true in the winter months ( 2 here ). When the wind was blowing fairly stiff and it was really cold ( yeah, I know, not cold here to all the northern folks ) the temperature would not stay where I put the thermostat. I had to resort to 2 or 3 of those electric space heaters to keep warm and comfortable.

The 2 speed furnace allows me to use less heat than before most of the time unless it will not keep up and then it will kick into max mode and should get the job done. My old furnace put out 80,000 btu when it was running. This new one is going to put out 57,200 most of the time and 88,000 if needed.

 

The unit is in and working excellent. This new thermostat is keeping the house temperature within 1° of where I set it. My old one was plus or minus 2°.

 

I have a 70 pint Dehumidifier that I keep set to the desired humidity level. I find the humidity harder to control in the months of the spring and fall, like now. The temperature outside is in the mid 70's so the AC rarely runs. It is rainy / humid and the humidity creeps up in the house. While they were installing yesterday and the front door was open and the stairway into the attic was open the humidity in the house went up to 87%. I like it 70 or below if possible.

When it goes up the Dehumidifier runs and starts removing moisture. In these months I empty the tank on it twice a day.

My 89 year old mother has one and she wants to know, "if there is that much water in the air why can't we see it ?".

 

Edit / Add: I found this video that shows how the 2 stage compressor works and the exact percentage it is running at in the low stage. It is 67%. This would make the 5 ton unit I have act like it was a 3.35 ton unit in the low stage.

http://www.youtube.c...h?v=uPhthHuZsQk


Edited by jimmie57, 31 October 2013 - 08:45 AM.

DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
HR24-100 Component cables to 46" Samsung LCD & Optical Cable to Yamaha AVR, H21-200 HDMI to Yamaha AVR & HDMI to 52" Mitsubishi LCD


#8 OFFLINE   Getteau

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Posted 31 October 2013 - 01:04 PM

If you have a multi-story house, be careful with the Auto setting.  I had my two units set to Auto and the upstairs and downstairs units ended up fighting each other.  Upstairs thermostat thought it was too hot, so it turned on the A/C.  The downstairs unit thought it was too cold so it turned on the heater.  Rinse and repeat till I noticed the heater was on during the summer.


Thanks,
Rich

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HR24-100 - HDMI to Panasonic TC-50S1 50" Plasma
HR23-700 - HDMI to Insignia 42" Plasma
HR22-100 - HDMI to LG 32" LCD
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R22-200 - Component to Insignia 42" Plasma
R15 - svideo to Toshiba 32" tube tv


#9 OFFLINE   jimmie57

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Posted 31 October 2013 - 02:01 PM

If you have a multi-story house, be careful with the Auto setting.  I had my two units set to Auto and the upstairs and downstairs units ended up fighting each other.  Upstairs thermostat thought it was too hot, so it turned on the A/C.  The downstairs unit thought it was too cold so it turned on the heater.  Rinse and repeat till I noticed the heater was on during the summer.

Yep, that would not be good.


DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
HR24-100 Component cables to 46" Samsung LCD & Optical Cable to Yamaha AVR, H21-200 HDMI to Yamaha AVR & HDMI to 52" Mitsubishi LCD


#10 OFFLINE   scooper

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Posted 31 October 2013 - 02:27 PM

TRH - I like the picture, but what does it MEAN ?

I'm just barely in Zone 4 (just north of Raleigh NC)


You CAN put antennas on your owned and/or controlled property...

http://www.fcc.gov/mb/facts/otard.html

#11 OFFLINE   trh

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Posted 31 October 2013 - 06:06 PM

TRH - I like the picture, but what does it MEAN ?

I'm just barely in Zone 4 (just north of Raleigh NC)

 

The zones are based on historical temperature data (heating and cooling days) and humidity.  The zones recognize that a house in the north needs to be built differently than one in the south.  The zones specify some minimum parameters when building a new house (to meet energy codes). For your zone 4, R-38 ceiling insulation, R-13 exterior walls, R-19 floors and window U-factor of 0.35.



#12 OFFLINE   trh

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Posted 31 October 2013 - 06:08 PM

To the TS: the design value for AC units is 50% relative humidity.  If your previous unit and dehumidifier couldn't maintain your house at that level, then you probably have some serious air infiltration problems** and/or the unit was over-sized and it wasn't running enough to properly dehumidify your house.

 

**By serious, I mean something that weather stripping couldn't fix. Major holes or even disconnected ducts in the attic.

 

What calculation was done that said you needed between a 4-5 ton unit?



#13 OFFLINE   gov

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Posted 31 October 2013 - 06:35 PM

I am in region 5 and have been pretty disappointed with a commercial property with 3 heat pumps.  The biggest ($$$) drawback is the electric backup heat.  It wasn't my decision, but the backup heat should have been propane.  What we all save with the heat pump in an hour when its 40 degrees out, we burn up in a minute when its 10 degrees outside with our expensive electricity.

 

Also, not the HVACs fault, but the builder/electrician did not put enough capacity in the meter/kill switch outside, (we had heavy enough wiring inside fortunately) and we were out over $1000 on a 2 year old building (first winter was mild) upgrading his mistake.  You could turn up the thermostat on 2 units when trying to get open for business on a cold day and knock out the electric service until somebody could stop by and unlock the cabinet and replace the fuses. GRRR.

 

In 4 years, we've had an outdoor compressor die, we've had a condensation pan crack (and cause quite a bit of water damage to a ceiling), we've had an A coil leak out all the refrigerant, we've had condensation issues on some ductwork dripping and causing more water damage (and the installer charged us $$$ for duct insulation and we had to install it) and we've had to put up with noise and appearance issues because nobody thought out where to put all the equipment.  We spend quite a bit on heating and cooling a large storage area because somebody (not me!) mistakenly told the HVAC contractor that space was going to be an office.  We also can't run the fart fans in the public restrooms because the HVAC pack for that part of the building is undersized and can't keep with the humidity in July and August.

 

That's quite a bit to go through on a new building.  Hope everyone else has better luck!

 

:righton:



#14 OFFLINE   jimmie57

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Posted 31 October 2013 - 07:18 PM

To the TS: the design value for AC units is 50% relative humidity.  If your previous unit and dehumidifier couldn't maintain your house at that level, then you probably have some serious air infiltration problems** and/or the unit was over-sized and it wasn't running enough to properly dehumidify your house.

 

**By serious, I mean something that weather stripping couldn't fix. Major holes or even disconnected ducts in the attic.

 

What calculation was done that said you needed between a 4-5 ton unit?

In the summer time when the temps got above 95 my old 4 ton AC would turn on at about 9:30-10 am and not turn off again until 9:30-10pm. Humidity would be 60 to 65 and the temp in the house would be 80 from about 3 pm to 7 pm. House is 2,240 square feet single story, no shade trees that block the sun from beating down on the house.

I have every single inch of duct work replaced with this new unit. There were also serious leaks in the return air closet from when I tore out a wall between 2 bath rooms and turned it into one large one for my son and his wheel chair. I did not realize that the contractor for the bath had opened that up until we started looking for the contractors to bid on the new AV system.

 

I probably could stop some of the humidity with some caulking also. However, we almost never go out of the house and I think the air in the house might get very stale if it was sealed really good so we can live with it if it leaks some.


DirecTV customer since 1996 - Current :Slimline 3 SWM,   HR24-100 HDMI to 32" Sharp LED,
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#15 OFFLINE   trh

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Posted 31 October 2013 - 08:44 PM

Smart idea to replace the duct work when you were doing the rest of the work. And fixing the return air closet will help also.

 

New homes are so air tight that they almost have to have mechanical air ventilation to ensure fresh air gets into the house (it's a requirement in Energy Star qualified homes). By controlling the air that 'leaks' into the house, you control the quality of the air.  You don't want air being drawn into the house from the garage (fumes from paint, pesticides, and car exhaust) or the attic (probably 140 degrees or higher in the summer time in your area). 

 

Hope your new system works well for you and your family.






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