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Old 05-10-2013, 05:52 PM   #16
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1993 basement HVAC question


I have branch returns to a main return duct in my ranch house in MD. In fact, I have an upper and a lower, the lower being adjustable. I find it very strange that they don't do this in AZ where it gets up over 100 degrees on a regular basis. Of course its not bad because its a dry heat

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Old 05-11-2013, 03:34 AM   #17
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and of course the answer to the dry heat statement is..... well, so is an oven!!!!!!

Phoenix, especially in the 1990's was a boom town. in fact phoenix has been a boom town for almost all of its history.

It is interesting that you have a basement. THAT is really rare in phoenix. The story goes that the ground was to hard back in the old days to dig basements, so slabs were used and were found to be cheap and fast, so no basements in phoenix. Heck in the 1950s through 1970s no garages were built.. carports were all the rage!!!!

back to your return question.. well you guessed it.. a single return was cheap and easy to build.
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Old 05-11-2013, 10:38 AM   #18
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1993 basement HVAC question


I'm blessed to have a basement here in Phx. I just hope it doesn't leak!! lol

Most builders say there are two types of basements, the ones that leak and the ones that are GOING to leak. I suppose that's true in most areas, but in Phoenix where we get 3 inches if we're lucky a year, I suspect it wont leak. THere's just no ground water unless you dig 100 feet.

I've spoken to others with basements and all said they never had a leak problem. But what we do have is a termite pandemic.

Regardless, I spoke to several HVAC guys on the phone yesterday about load calculations for the basement. Some wouldn't even talk about it and others said it's not needed since it's a basement. A bit worried about contractors who think this, but then again, it makes sense. They told me there are NO windows and it's completely insulated by dirt!

My basement is 900 sq ft. They all said the load calcs might say 2.5 ton, but because it's a basement and so well insulated, especially in Phoenix, most said a 2 ton would be MORE than enough.

Thoughts about not doing a load calc in a basement?

I decided against a split system as some have recommended and do two separate heat pumps. a 4 ton for the upstairs (1700 sq ft) and a 2 ton for the basement.

I just need to figure out a duct design.

The more I research DIY HVAC work, the more complicated it becomes. Duct design might be over my head. I thought you just run the ducts to the room and you're good. Guess not.

My plan was to utilize the duct work already in place for the basement and seal off the ducts that branch up to the main floor. But now I'm thinking the ducts may not be large enough??

No clue.
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Old 05-11-2013, 11:04 AM   #19
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So I calculated my main floor. Does this mean a 4 ton would be too big??? Why is every contractor telling me a 4-5 ton is suffice? I'm pretty sure I calculated correctly..

TOTAL COOLING BTUs - 36678
SENSIBLE - 35678
LATENT LOAD - 1000
TOTAL HEATING BTUS - 35919
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Old 05-11-2013, 11:52 AM   #20
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First of all I would get rid of the existing unit as fairly soon the compressor will die from old age/usage and at $1500-$2500 to replace it not worth doing plus a Freon leak may occur in a coil etc.

Second the ductwork needs to match the unit capacity and be professionally done or it can freezeup the AC from poor flow or whistle etc. Doubt your old ducts will work and may not be the right size.

Sounds to me like you need to find a contractor who can size the unit properly and design a PROPER set of ducts and give you good advice based on your floor plan. Heat rises and I would ignore the basement. Has no heat gain from dirt so they are right it won't add to your cooling load. Sounds to me like you are going to do a complete makeover of the system and or should do one otherwise you won't be happy in the long run or get good circulation in your rooms. That old RUUD is not very efficient and especially in your climate you want the most efficient AC like I want the most efficient furnace in mine. Likely it is a 8-10 SEER and that was on it's best day.

Another good option would be to go with a ductless minisplit system or 2 and rip out the old system. They make heat pumps and you can get units with up to 4 heads/blower units off one unit. Depends on the layout of the rooms whether they can get the piping etc to them but they are incredibly quiet and efficient. Fujitsu is my favorite and Mitsubishi is good too.
http://www.fujitsugeneral.com/wallmounted9-12RL.htm
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Last edited by yuri; 05-11-2013 at 12:01 PM.
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Old 05-11-2013, 12:06 PM   #21
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Quote:
Originally Posted by yuri View Post
First of all I would get rid of the existing unit as fairly soon the compressor will die from old age/usage and at $1500-$2500 to replace it not worth doing plus a Freon leak may occur in a coil etc.

Second the ductwork needs to match the unit capacity and be professionally done or it can freezeup the AC from poor flow or whistle etc. Doubt your old ducts will work and may not be the right size.

Sounds to me like you need to find a contractor who can size the unit properly and design a PROPER set of ducts and give you good advice based on your floor plan. Heat rises and I would ignore the basement. Has no heat gain from dirt so they are right it won't add to your cooling load. Sounds to me like you are going to do a complete makeover of the system and or should do one otherwise you won't be happy in the long run or get good circulation in your rooms. That old RUUD is not very efficient and especially in your climate you want the most efficient AC like I want the most efficient furnace in mine. Likely it is a 8-10 SEER and that was on it's best day.
Good info. Yes a total remake, but I'm pretty handy and added a complete second story to my old home in Oregon. The heating there was totally different with oil. Regardless, I'm confident of doing this entire remodel myself except the HVAC work. However, I would like to do AS MUCH as possible to save cost. Like running the duct work, etc. I would even want to install or place the unit and handler except for the actual hook up.

I'm reading a thread on here from February that has alot of info on duct work , etc but it's pretty technical.

I'm kinda chuckling at the fact that some on her are adamant about load calculations while others are saying despite the calculation, it's not taking into consideration certain needs about weather fluctuations, monsoon seasons, etc...So some on here are reverting to the 400/per ton calc. Others are saying that even though the calcs say for example 3 ton unit in my situation, it's best to go a bit higher to be more comfortable when here in Phoenix, we have the monsoon season in August and temps hit 120....

So it seems all the info I'm finding at times, contradicts the Manual J calcs, or is off a bit...
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Old 05-11-2013, 01:00 PM   #22
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Manual J tells you the capacity an A/C needs at the design conditions. Not what size A/c has that capacity at those design conditions.

What design conditions did you use when you got those results.
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Old 05-11-2013, 01:08 PM   #23
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Originally Posted by beenthere View Post
Manual J tells you the capacity an A/C needs at the design conditions. Not what size A/c has that capacity at those design conditions.

What design conditions did you use when you got those results.
Yeah - I misquoted that with all the Manual research I've been doing.

What do you mean "design conditions?"

Indoor cooling temp - 76
Outdoor - 108
Indoor humidity - 45
(the calc wouldn't let me go lower, but int he peak summer of AZ, our monsoons reach 45 humidity with 110 temp). lasts 2-3 months

Indoor heating - 78
outdoor - 50
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Old 05-11-2013, 01:16 PM   #24
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Design conditions, are the "conditions" temp and humidity the A/C is to cool the house to at what outdoor temp.

An over sized A/C won't remove humidity right. Your normal design temp is only 2 degrees cooler then your monsoon season temp. nothing to worry about.

You nee to find an A/C that has a 35,678 BTU sensible capacity at 108 outdoor temp and 76 indoor temp. No 3 ton will have that capacity. All A/Cs are capacity rated at 95 degree outdoor temp and 80 degree indoor dry bulb with 67 degree wetbulb.
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Old 05-11-2013, 01:22 PM   #25
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Originally Posted by beenthere View Post
Design conditions, are the "conditions" temp and humidity the A/C is to cool the house to at what outdoor temp.

An over sized A/C won't remove humidity right. Your normal design temp is only 2 degrees cooler then your monsoon season temp. nothing to worry about.

You nee to find an A/C that has a 35,678 BTU sensible capacity at 108 outdoor temp and 76 indoor temp. No 3 ton will have that capacity. All A/Cs are capacity rated at 95 degree outdoor temp and 80 degree indoor dry bulb with 67 degree wetbulb.
Thank you. So despite looking everywhere online, I can't find anywhere that would provide this type of info. This is the type of confusion I'm dealing with. Maybe it's because I just don't understand it. According to the calcs, a 3 ton should do the job? 3 ton = 36,000, no? But you're telling me based on my conditions, I need something more. How are you figuring this out?

I'm looking at buying a 1 year old used Trane 4 ton XL20i and matching Trance air handler and am trying to figure out if it would work.
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Old 05-11-2013, 01:28 PM   #26
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I wouldn't buy a used Trane 20i. With no warranty. if one of the compressors goes out. You are looking at some big bucks to replace one, if not both compressors.

You need to look at the extended performance data. Trane calls it "service facts". This has the BTU capacity at different outdoor temps.

A 3 ton A/C is not 36,000 BTUs. 3 tons is a nominal rating. And only at 95 outdoor temp, and 80 degree indoor temp at 67 degrees wetbulb.

Its like the EPA MPG rating of a car. 27 MPG highway. Try driving at 110 on the highway and see if you get 27 MPG.
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Old 05-11-2013, 01:31 PM   #27
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Quote:
Originally Posted by beenthere View Post
I wouldn't buy a used Trane 20i. With no warranty. if one of the compressors goes out. You are looking at some big bucks to replace one, if not both compressors.

You need to look at the extended performance data. Trane calls it "service facts". This has the BTU capacity at different outdoor temps.

A 3 ton A/C is not 36,000 BTUs. 3 tons is a nominal rating. And only at 95 outdoor temp, and 80 degree indoor temp at 67 degrees wetbulb.

Its like the EPA MPG rating of a car. 27 MPG highway. Try driving at 110 on the highway and see if you get 27 MPG.
That makes sense. I thought heat pump warranties were transferable? Well at least if the original owner purchased the transfer option. I can't find any facts about "service facts" on their website.

Last edited by Daugela; 05-11-2013 at 01:39 PM.
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Old 05-11-2013, 01:40 PM   #28
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I pulled up a York 18 SEER 3 ton 2 stage.

At 95 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 34,200 BTUs, at 1250 CFM.
At 105 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 32,000 BTUs, at 1250 CFM.
At 115 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 29,800 BTUs, at 1250 CFM.

A York 4 ton 18 SEER 2 stage.

At 95 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 42,900 BTUs, at 1750 CFM.
At 105 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 40,100 BTUs, at 1750 CFM.
At 115 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 37,400 BTUs, at 1750 CFM.
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Old 05-11-2013, 01:41 PM   #29
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That makes sense. I thought heat pump warranties were transferable? Well at least if the original owner purchased the transfer option. I can't find any facts about "service facts" on their website.

If your buy the house its installed, and use it there. But if you buy it and move it, its not.
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Old 05-11-2013, 01:45 PM   #30
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Quote:
Originally Posted by beenthere View Post
I pulled up a York 18 SEER 3 ton 2 stage.

At 95 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 34,200 BTUs, at 1250 CFM.
At 105 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 32,000 BTUs, at 1250 CFM.
At 115 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 29,800 BTUs, at 1250 CFM.

A York 4 ton 18 SEER 2 stage.

At 95 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 42,900 BTUs, at 1750 CFM.
At 105 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 40,100 BTUs, at 1750 CFM.
At 115 outdoor temp, indoor of 75 at 48%RH it has a total capacity of 37,400 BTUs, at 1750 CFM.
Well now, 4 ton it is....I will have to check this with other manufacturers. In general, do most 4 ton have this rating?

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