Houston: 3.5 tons for 5,200 sq ft house?

[uktra]

Guys--I am finding "educating mrbillpro" a lot of fun! Mrbillpro--do a google search on Building America--click research projects on left. Click picture of Texas (thats the big state on the bottom thats large, like their a/c units). Click on Houston (thats a large city in large Texas that has large a/c's--You guys love large don't ya!)
You will find 14 subdivisions (that's large!) from 3 builders in this program. Find out the HVAC contractors and talk to them. Talk to the customers. I know this is a large task, but I know you are up to it.

[Panama]

Originally posted by dan sw fl

Originally posted by mrbillpro

Originally posted by uktra
Do we have the correct imput on our calcs and do we design the house for the few days of abnormal conditions?

... 5200 sq. ft. home
... a lot of occupants or a lot of parties call it abnormal conditions may be perfectly normal to some and you brought up a good point as to why you can't totally rely on old J & D. ...
[Edited by mrbillpro on 06-29-2005 at 10:37 PM]

Simplifying___
Windows ......11,000 BTUh ( 600 S.F. + )
Ceiling....... 6,000
Walls......... 5,000
Floor......... _____
Duct ......... 4,000
Infiltration . 4,000
Internal Gain. 4,500
People ....... 3,500
TOTAL ........38,000 BTUh +++
_______ THAT'S in a PERFECT (VIRTUAL) WORLD.

35' x 70' = 2,450 x 2 = 4,900 S.F.

How does one get < 4-ton to maintain
77'F at 92'F outside temperature?
I suspect that a _4-ton may cool home
to _14'F less than the Outside Temperature.

& __5-ton _17'F

Window area as stated
( Glass to Floor area ratio = 11% )
DOES lean towards a
"Cave Like" Environment.

NOTE that this VIRTUAL house has ONLY 75 S.F.
of glass on the EAST and WEST Sides.
.. Just Ain't GOING TO HAPPEN IN REALITY
... perhaps, a 1 in 280,000 real world chance.

This is a GREAT THREAD
which ENABLES people to _STRETCH Their VIRTUAL Minds.

However, most people visiting HVAC-TALK forum
will need to STAY IN REALITY.

Very good, Dan.

I used a 15% glazing ratio on the first floor and 10% (code minimum) on the second floor. This should be quite satisfactory for those interested in lowering their utility bills. Putting most of the glazing on the north and south just makes good sense if the orientation and interior layout of the house permits.

But you don't say whether your figures are sensible or total. You seem very high on the ceiling, duct losses, and internal gains that you don't explain. I used R-38 for the attic and J7 duct losses only for the 2nd floor.

I suspect you never use manufacturers' engineering data to select equipment. This is a major mistake by most people in the HVAC industry. I suggest you take a look at some, as it can be very enlightening. You also might get a copy of ACCA Manual S; it's an outstanding booklet that explains all sorts of things that are usually ignored.

[Mr Bill]

Originally posted by trane
Yes but then again there is no perfect size for any house due to changing outside conditions.

uktra, I do sincerely appreciate your thoughtfulness "and I really mean that" but I got to get right now to many calls, but I will check that out when I get some time but I think what trane above said pretty much says it all. Happy A/Cing and have a safe 4th.

[bluetooth751]

I assume the home must have 2x6 exterior walls.

Don't try to cool the 2-story home with one system.

I would talk with the homeowner and learn some of their habbits before I size the equipment.

Manual J does work it was made by a group of people who probably are alot more intelligent than us.

You can't size an air conditioner because the homeowner has two parties in the home every year. Oversized 363 days sized right 2.

[Panama]

Originally posted by uktra
The other big question on the theoretical home is : are the ducts and air handler inside conditioned space? If they are, then a 3 ton will work fine. For all those like mrbillpro that don't think it will work, I suggest they visit some Building America homes in his area and talk to the customers that bought them. He also might want to read Home Energy magazine (july/August 05) just out, about a customer in West Columbia, Texas. People are becoming more educated through the internet and demand it be done right. The old "insufficient air movement" b.s. and "I have been doing it this way for 25 years" won't cut it anymore.

Uktra,

I read the Home Energy article this morning. Thanks for directing me to it.

Paul Blaha probably made more money by listening to his customer than Mr. Bill would have by hooking up a couple of Goodmans to some flex duct. Those 2-stage Lennox systems ain't cheap.

Thanks for all your support. Have a great Independence Day.

PNM

[classical]

Well Uktra you still haven't said where you live that has a climate like Houston.

I read the article and looked up Houston area homes. Looks like there about 600 around here. I have been to several of these neighborhoods and dealt with homes that will not stay comfortable over 95 degrees. In fact my Chiropractor owns one and we are going to have to redo the ductwork and add more capacity so they are comfortable in their game room and the upstairs bedrooms.

[pstu]

Are there really true stories of the Houston Area "Building America" homes not cooling OK? I am very interested in what I can learn from this.

Is it because the actual heat gain is higher than calculated? Is the AC system not delivering enough cooling BTUs? Latent BTUs? Sloppy work by Pulte?

If anyone can provide facts to answer any of those questions, that would be extremely interesting and educational. Since I live near Houston, very relevant too. To me this amounts to a revival of the old question whether Manual J is the right tool in this hot-humid climate. Most of the people who say it isn't don't seem to have enough vocabulary, or math background to explain why. Answers from this angle might supply the missing argument.

Thanks in advance -- P.Student

[Mr Bill]

Originally posted by perpetual_student
Most of the people who say it isn't don't seem to have enough vocabulary, or math background to explain why. Answers from this angle might supply the missing argument.

So my guess with a statement like that you believe everything you read, So do you believe everything you read? or is it possible that some of us think outside the box of things figured in a classroom or lab and have been to a live home and seen how these numbers perform in a real world? The only perfect writings are the inspired word of God that I trust 100%. I can't say as to how these numbers perform in the real world like Al "classical" can he has been to one, but you can bet you last dollar that I will visit one of these homes soon and I will post an exact statement here from the HO, I think that would be fair.

[uktra]

Perpetual Student--I suggest you check into these homes yourself. I think you will find these homes work much better than the usual code built homes. You have to ask yourself, if they don't work as advertised and people were uncomfortable, why are there 14 subdivisions and over 600 homes?

Classical--Anyone can have a problem--nothing is perfect. An example of one problem doesn't prove anything. Document how many real capacity problems are in these homes. If you can't do that then you are just (as they say in Texas) "pissin' in the wind"

[Special Ed]

I've noticed that Panama & Uktra have posted to what amounts to mostly theory & Mrbillpro has posted mostly on experience. I trust experience.

And to say that most A/C's in TX. are over-sized is absolutely incorrect! In fact, if the figures are done right then - in theory - no A/C has been over-sized. It all depends on the house & how it's built that determines the size of the A/C not how it should be built. In other words, you gotta figure out the heat load.

Still, 3 1/2tons for a 5200sq.ft. two-story house? I have my doubts. Even if it was possible you would still have to zone it, at least. Or maybe a 2ton system for downstairs & a 1 1/2ton for upstairs. Or....

[uktra]

special ed--This is not theory, I help design and build homes in the real world.

P. Student--Pulte homes of Houston is rated number 1 in fewest problems by J. D. Power for the Houston area in 2004.

[trane]

I just want to bring up a few thoughts and see if you guys agree or not.
Manual J is only as good as the numbers you put into it and will fail if something is missed.

Manual J assumes on the homeowners behalf how cool he will keep his house on days the temp is above design

You normally have to over or undersize the A/C to get closest to manual J loads

Every A/C unit installed is not the perfect size all the time

Although I don't live in Texas, I would think adding up to 1 ton over Manual J loads would not be a problem in most cases and the customer would notice little difference in the humidity level or the electric bill

And Last- The customer is the one we are trying to make happy. Make them aware of what the new system will be designed for (before installation) and make sure this is what they want or change it to their needs.

[classical]

Uktra when I have the time I will ask if I can post specifics about a home.

Well I bet any amount of money Uktra works for Pulte!

J.D. Powers is just like any other survey not worth squat.

The same type of thing that rates Trane/Am/Std as the best A/C please. J.D. Powers also ranked Oldsmobile as the top auto for years; lets see they went out of business after nearly a Century. The same survey company that at the same time ranks Ford Chevy and Dodge as the best built or best selling truck in Texas. The survey produces what the marketer wants it to produce, as do all polls. It is in how you ask or phrase the question.

I have been in homes built by every builder in Houston for 35 years. I will grant Pulte does build a better than average home but that isn't saying much around here. I haven't seen a home built in the last 20-years would buy. My next home I will build from the ground up.

Regardless of the builder all new homes have one common denominator the A/C Plumbing and electrical are the cheapest items in the house and always go to low bidder. I have yet to see a track homebuilder pay more than $1,500.00 per ton for the A/C.

[Special Ed]

Originally posted by uktra
P. Student--Pulte homes of Houston is rated number 1 in fewest problems by J. D. Power for the Houston area in 2004.

Not for long if they put a 3 1/2ton system on a 5200sq.ft. two-story house.

[uktra]

Classical--you are wrong again--I do not work for Pulte. While you put down J. D. powers survey can you produce a better survey of home buying customers? If there were all these under capacity problems you claim Pulte has, why isn't this reflected in the owner surveys? Again you are "pissin' in the wind".

Special ed --read the thread, no one ever said Pulte was putting 3.5 ton in a 5200 sq. ft. home.

[Edited by uktra on 06-30-2005 at 09:42 PM]

[pstu]

MrBillPro said:

>>So my guess with a statement like that you believe everything you read,
>>So do you believe everything you read? or is it possible that some of us
>>think outside the box of things figured in a classroom or lab and have been
>>to a live home and seen how these numbers perform in a real world?

MrBill, I would much prefer you show me wrong and explain WHY or HOW these homes fail to perform. Yeah I was baiting the Manual J doubters just a bit but you have not lessened my doubts at this point. I do respect that you have much real world experience, I do notice that you are skeptical of Manual J but don't necessarily believe in those things written by you or some others. If only I could hear a plausible theory of WHY or HOW Manual J fails to deliver satisfactory comfort, then I could come around and be much more sympathetic to your views.

I am not saying that you are wrong, however I am waiting for something more persuasive than "I seen it" testimonials. Because if you haven't noticed, there are a lot of people who say "I seen it" in favor of Manual J working.

Myself I have received quotes from AC guys who claim my 2 systems are undersized at 7.0 tons. One guy wanted to up me to 9.0 tons, of course that would require all new ductwork and the price of a pretty good car. Yet my house cools OK, one system is measured at 73% duty cycle and the other at 93% (as measured by minutes on vs. off in the peak hour). Is that not serious evidence I don't need 9.0 tons? Just who is thinking inside a box here?

Regards -- P.Student

[trane]

Originally posted by perpetual_student
MrBillPro said:

>>So my guess with a statement like that you believe everything you read,
>>So do you believe everything you read? or is it possible that some of us
>>think outside the box of things figured in a classroom or lab and have been
>>to a live home and seen how these numbers perform in a real world?

MrBill, I would much prefer you show me wrong and explain WHY or HOW these homes fail to perform. Yeah I was baiting the Manual J doubters just a bit but you have not lessened my doubts at this point. I do respect that you have much real world experience, I do notice that you are skeptical of Manual J but don't necessarily believe in those things written by you or some others. If only I could hear a plausible theory of WHY or HOW Manual J fails to deliver satisfactory comfort, then I could come around and be much more sympathetic to your views.

I am not saying that you are wrong, however I am waiting for something more persuasive than "I seen it" testimonials. Because if you haven't noticed, there are a lot of people who say "I seen it" in favor of Manual J working.

Myself I have received quotes from AC guys who claim my 2 systems are undersized at 7.0 tons. One guy wanted to up me to 9.0 tons, of course that would require all new ductwork and the price of a pretty good car. Yet my house cools OK, one system is measured at 73% duty cycle and the other at 93% (as measured by minutes on vs. off in the peak hour). Is that not serious evidence I don't need 9.0 tons? Just who is thinking inside a box here?

Regards -- P.Student

There is no problem with manual J. If everything is exactly like the values you use to determine the load which is easier to do in a new home and harder to do in a existing home. It leaves little room for error if a mistake is made or a guess at insulation in the walls are wrong. My biggest problem is homeowners not knowing in advance what the system will do in the extreme temps. All of my customers would rather pay a little more in the milder months for being a little oversized than have to add a window unit or set and watch tv with a blanket over them. It is easy for someone to say manual J works every time but are they the ones that have to answer the phone on the days it gets above or below design temps and explain why the new system they installed won't keep up? How many furnaces and A/C units have YOU installed Uktra?

[Edited by trane on 06-30-2005 at 11:04 PM]

[dash]

30 years in HVAC in Florida ,over 7000 new construction homes,manual J has yet to undersize a home.Now we have had a few,where the info. was wrong or the person inputing the data made an error,and undersized a home.

[uktra]

Trane--How many homes have you designed that you guaranteed HVAC monthly costs, humidity levels, and temps no more than 3 degrees room to room?

[trane]

Dash, it depends on who is deciding if its undersized? I agree that if all of the home owners are happy with the design temps you use your doing what your customers want and manual J will work for you. He asked why manual J has failed and I tried to point out some reasons. I also never doubted your installation skills but do Uktra's.