Completely Stumped

[wdj03]

Hey folks, nice to find you here. I've got a puzzling situation with my system. (Sorry, this is very long, but I'm trying to include all of my info at once instead of making you guys ask me..) For the past 2-3 years, it's done a very expensive and poor job of cooling my house.

Symptoms:
First off I live in coastal South Texas, so heat & humidity are both extreme here. My programmable thermostat is set at reasonable levels - 77 in the evening, 76 at night, 79 during the day (no sense in setting it any lower). Once the outside temps come up, the AC is outmatched. It quickly climbs to 80-81 and stays there all day. The unit turns on at about 11am, and doesn't turn off until midnight or later. My electric bill for April was about $275 and May was $350. I wouldn't be suprised if I got past $400 this August.

Technical Info:
- My house was built in 1978, I purchased it about 5.5 years ago. It's about 1,850 square feet, with mostly 8' ceilings, bringing interior volume to about 15,000 cubic ft.

- We replaced the furnace/evaporator unit about 3 years ago, but still have the original condenser. Both units are sized the same (either 3.0 or 3.5 ton, I don't know which but I've been told that it's the correct size by at least 2 or 3 folks).

- Yes, it's easy to suspect a 28 year old condensor, but I have it checked every year and the guy says that there's just nothing going on with it that tells him that it needs to be replaced.

- In two rooms (550sqft), I had poor ventilation but good (R-39) insulation. In the rest of the house (1300ft) I had adequate ventilation, but extremely poor (R-10 maybe?) insulation. Over the winter, I added ventilation in the two rooms. Yesterday, I had R-30 blown into the rest of the house.

- My ductwork has been tested and is nice & tight, so I'm not blowing cool air into the attic.

- I've sealed around all of my vent openings, and 99% of the other spots with openings or non-insulated access into the attic.

- My wife does a good job of keeping up with the filter, and I have my inside & outside coils cleaned each year (during the checkup).

- The split between my intake and vent temperature is respectable. At the vent nearest the unit (about 3' away) the split is 19-20. At the vent farthest from the unit (30'+) it's 18-19.

My thoughts:
I always assumed that the silver bullet would be getting my attic adequately insulated. I put that project off because I kept telling myself that I'd DIY and save some money. I finally got over that stupid idea and payed someone to do it yesterday. Unfortunately, it only got about 1-2 degrees better.

Yes, I have a few minor details to finish (a few more soffet vents, sealing around some openings, recaulking windows, etc..) but I can't see any of those things making up for the high temps & huge bills that I'm getting.

For one comparison - My in-laws live a mile away, have a house that's 20% bigger, stays 4-5 degrees cooler (with the unit cycling on & off properly), and their bill is less than half what mine is.

As far as I can see, the only major thing that is left is to replace the condensing unit. Do you guys see any other options? What's the general opinion for best bang-for-the-buck on the market for a new outside unit?

[BaldLoonie]

Attic duct heat gain.

Not fun BUT wait til the hotest part of the day. Get a digital probe type thermometer. Get up in the attic, take a wet rag with you or cold drink as it will be brutal. Stick the probe in the return duct as the air enters the blower unit. Then stick the probe in the supply duct a foot or 2 from the outlet of the unit. The difference should be 15-20 degrees on a good working system with proper airflow. But that's not the real test. Then get out of the attic if you haven't passed out yet. Take temps at the intake return grills and compare to the return at the unit. Then do the same at the supply grills. See how much heat is gained between the grills and the unit.

I had a rich guy couldn't cool his upstairs 2 rooms with a 3 ton. Turns out that over 1/2 of his capacity was going to remove heat picked up from the attic in the supply & return ducts. That 1" of insulation surrounding your flex duct has a real problem keeping the 150° attic heat out.

[wdj03]

No worries about getting in the attic.. I did this test last summer. My father in law is a home inspector, so he had the thermometers.

My A/H is in a closet, so I only have one return grille down near the floor. I put one thermometer in that grille. I have a vent about 3' from the supply duct coming out of the unit, and I put the other thermometer in there.

I tested about 5 times, swapping thermometers each time. Return temps were consistently 80-81, supply was consistently 60-62. I also checked at the duct farthest from the unit - about 30' through the attic. I only gained 1-2 degrees.

Also, my ducts are hard, not flex.

[Mr Bill]

You must be a mind reader! that scares me :D I was going to tell him the same about checking the TD in the attic and not at the return and then go back and recheck it at return and supplys.

[Mr Bill]

Could very well be if that condenser is that old the condenser coil has lost a lot of it's integrity and cannot keep up with the heat removal needed, unless like baldie said your picking up a ton of heat through the duct system that's very possible.

[wdj03]

The only other idea I can think of is related to air flow.

If I'm not pushing enough CFM's through my evaporator, then my split will look good but there won't be enough volume to cool my house.

How can I:
A) Check to see how much air I'm pushing
B) Check to see how much I need to push
C) Adjust A to equal B

I don't have a manufacturer or model # on my A/H with me right now, I'll get that when I get home tonight..

[wdj03]

Originally posted by mrbillpro
Could very well be if that condenser is that old the condenser coil has lost a lot of it's integrity and cannot keep up with the heat removal needed, unless like baldie said your picking up a ton of heat through the duct system that's very possible.
If this was the case though, wouldn't my split be less than 18-20 degrees?

[trane]

What kind of filter are you using?

[bornriding]

FRom my experience being in the south ( S. Bama ) - If the unit is a 3 ton, then you are undersized.
I the unit is 3.5 ton, then yu have other issues, but ones that a good tech should discover.
At 1850 sg ft, without much humidity, you are pushing the very limits of a 3 ton system, with the insulation you stated, and the age of the home.

Richard

[billva]

Originally posted by wdj03

Originally posted by mrbillpro
Could very well be if that condenser is that old the condenser coil has lost a lot of it's integrity and cannot keep up with the heat removal needed, unless like baldie said your picking up a ton of heat through the duct system that's very possible.
If this was the case though, wouldn't my split be less than 18-20 degrees?

nope, they compensated with the refrigerant charge. if you can give pressures and line temps we can give more info.

[wdj03]

Originally posted by trane
What kind of filter are you using?
Not sure exactly what you're after here..

It's not the cheap old 3/4" blue things. I think the ones we buy run about $20 each and are a good 2"-3" thick.. I think they're HEPA, but I'm not sure.

We keep a spare in the closet, so I'll check it when I get home (I want to change it out in a day or two anyway due to the dust from the insulation install)..


Originally posted by FRom my experience being in the south ( S. Bama ) - If the unit is a 3 ton, then you are undersized.
I the unit is 3.5 ton, then yu have other issues, but ones that a good tech should discover.
At 1850 sg ft, without much humidity, you are pushing the very limits of a 3 ton system, with the insulation you stated, and the age of the home.
It might be 3.5 then.. Again, I'll check when I get home in a little while.. When I was getting the AH & ductwork done, I had the estimators (3 of them I think) tell me what a full system would cost. None of them reccomended sizing up.

[Mr Bill]

Well my home is 1940 sq.ft and I have a 4-ton system on it with a TXV coil and it cools fine cycles fine and the light bill is not that high compared to most horror stories I have heard mine was $159.00 last month and I am in Houston, heat and humidity capital of the world.
By the way I have a mixed matched of mfg's also, I have a Carrier condenser 12 seer and a Trane furnace and a Aspen 12 seer txv evap. and mine works great! and feel great! in the house. :D

[the dangling wrangler]

What kind of filter are you using? [/B][/QUOTE]
Not sure exactly what you're after here.. [/B][/QUOTE] Let's try something simple here . Try changing that 2 or 3 inch filter first. I don't think your system was designed for a 2 or 3 inch filter , too restrictive. If you slow down the blower , the temp will drop also . Try the simple stuff first. Go back to the cheap, throw away filter for a week and see what happens.

[dmitch]

Right check air filter, most older system are capable to keep enough cfm's your filters could be restrictive, stick one of those old blue ones in notice some difference

[trane]

Originally posted by wdj03
[QUOTE]Originally posted by trane
[B]What kind of filter are you using?
Not sure exactly what you're after here..

It's not the cheap old 3/4" blue things. I think the ones we buy run about $20 each and are a good 2"-3" thick.. I think they're HEPA, but I'm not sure.

We keep a spare in the closet, so I'll check it when I get home (I want to change it out in a day or two anyway due to the dust from the insulation install)..

________________________________________________

In most cases the installer needs to know that you are planning to use those types of filters so they can design the ducts and filter opening size to handle the added resistance created by the better filtering capability. What size is the filter you are using and what is the rating?

[wdj03]

Originally posted by mrbillpro
Well my home is 1940 sq.ft and I have a 4-ton system on it with a TXV coil and it cools fine cycles fine and the light bill is not that high compared to most horror stories I have heard mine was $159.00 last month and I am in Houston, heat and humidity capital of the world.
By the way I have a mixed matched of mfg's also, I have a Carrier condenser 12 seer and a Trane furnace and a Aspen 12 seer txv evap. and mine works great! and feel great! in the house. :D
$159? I do that in the winter.. hahaha..

I'm about 3 hours south of you mrbill, it's nice to have someone fairly local, yet not in my market. Even the reputable companies in my area seem a little shady from time to time. That's why I'm hoping to get a little bit of an education here..

I don't mind dropping the money on a new system and good installation if that's what I need to do. What I can't do is just have a snazzily dressed salesman come by, open my closet, look at my unit and reccomend their top of the line bright shiny new system.

If my outside unit is dying, fine. Show me the pressures & temps that lead you to that conclusion. If my system is undersized, show me a Manual J calc for what I have and then show me the Manual J calc for what I need.

Is this too demanding as a homeowner?

[wdj03]

Originally posted by the dangling wrangler
What kind of filter are you using?
Not sure exactly what you're after here.. [/B][/QUOTE] Let's try something simple here . Try changing that 2 or 3 inch filter first. I don't think your system was designed for a 2 or 3 inch filter , too restrictive. If you slow down the blower , the temp will drop also . Try the simple stuff first. Go back to the cheap, throw away filter for a week and see what happens. [/B][/QUOTE]
First off, my filter is a 25"x16"x4" (I think) I'm almost positive that my A/H is designed for it - I think I specifically requested that it handle the larger HEPA filters.

I appreciate the suggestions on the filter, but before I try this...

I tripled the insulation in 70% of my attic. That only got me 1 degree cooler. Is it really possible that a thinner filter is going to gain me 4-5 degrees?

[wdj03]

In most cases the installer needs to know that you are planning to use those types of filters so they can design the ducts and filter opening size to handle the added resistance created by the better filtering capability. What size is the filter you are using and what is the rating?
As stated above it's 25"x16"x4" (I might be an inch off in the 25 or 16, but it's close to that and it's definitely 4" thick..)

I'm almost positive that I did request and pay a little extra for that type of filter.. The box for the filters was installed with the rest of the A/H unit, so they knew what they were putting in.

By the way.. My furnace is a Ruud Silhouette II, 75,000 BTU gas. I found the manuals, but there wasn't any info on the coils or blower in it. Are those added as required by the installer?

[wdj03]

Sorry for blabbing so much, but one more piece of info..

I found a website for my installer, and he's a Ruud Top Contractor, with an ACCA Partnership logo on there, and NATE certified.. I don't know what all of that means, but it at least suggests that he's not a moonlighter.

This installer specified and installed the A/H, ductwork, furnace, and coil.

I will admit that the guy doing my checkups & cleanings is a retired Tech & business associate of my in-laws. I might call the installer for a checkup & cleaning this year.

[nina]

wdj03 wrote:
> show me a Manual J calc for what I have and then show me the Manual J calc for what I need.

you won't find many willing to show it as they may fear you take the results and shop elsewhere using their calculations

[Mr Bill]

Originally posted by wdj03
with an ACCA Partnership logo on there, and NATE certified.. I don't know what all of that means

Yep that's is normal, not many of the public do and this is why most of these folks need to advertise more so you will know or just shut down and stop taking our money.

[crowder]

It sounds like you may have an added heat load problem. I would check my attic ventilation system if you have one. I had the same problem with my mother-in-laws unit. It would run all day and only cycle at night or when it would rain and cool off outside. I could feel the heat coming from the attic when I would open the air handler closet door. Make sure the closet is not open to the the attic allowing heat to flow into your conditioned space.This will increase the heat load in the house,or maybe just around your thermostat causing a false heat load. I repaired my mother-in-laws attic fan and the unit started cycling like it was suppose to.

If you have a 3 ton unit and a 1800+ sq ft of living space. You are right on the borderline of being undersized without the added heat load. Rule of thumb is 500 to 600 sq ft per ton of cooling, depending on who you ask and what type environment you live in. I would of went with 500 sq ft per ton for your neck of the woods. Meaning I would have went with at least a 3.5 to 4 ton unit for both the inside and outside unit.

BEST PRACTICE
When replacing the outside replace the inside. Especially if one is twenty years older than the other. Systems are much more effecient now days than they were twenty years ago. Now you probably have a pretty effecient inside unit with a not so effecient outside. You've probably paid enough in power bills since you replaced the inside to replace your complete system a couple of times.

Hope this helps

[wdj03]

Originally posted by crowder
It sounds like you may have an added heat load problem. I would check my attic ventilation system if you have one. I had the same problem with my mother-in-laws unit. It would run all day and only cycle at night or when it would rain and cool off outside. I could feel the heat coming from the attic when I would open the air handler closet door. Make sure the closet is not open to the the attic allowing heat to flow into your conditioned space.This will increase the heat load in the house,or maybe just around your thermostat causing a false heat load. I repaired my mother-in-laws attic fan and the unit started cycling like it was suppose to.

If you have a 3 ton unit and a 1800+ sq ft of living space. You are right on the borderline of being undersized without the added heat load. Rule of thumb is 500 to 600 sq ft per ton of cooling, depending on who you ask and what type environment you live in. I would of went with 500 sq ft per ton for your neck of the woods. Meaning I would have went with at least a 3.5 to 4 ton unit for both the inside and outside unit.

BEST PRACTICE
When replacing the outside replace the inside. Especially if one is twenty years older than the other. Systems are much more effecient now days than they were twenty years ago. Now you probably have a pretty effecient inside unit with a not so effecient outside. You've probably paid enough in power bills since you replaced the inside to replace your complete system a couple of times.

Hope this helps
I do have an opening into the attic above my furnace & inside unit. And yes, it does seem pretty warm inside and around my closet. I would like to insulate it, but I thought that it's required to be open to the attic since I have a gas furnace.

As far as my ventilation goes, I'm pretty close to Owens Corning's reccomendations as far as total NFVA and system balance. I have a little bit of soffet vent work to do, but nothing major. I don't have any form of forced ventilation. I've read that this interrupts the normal soffet-to-ridge flow and makes your ventilation system less effective.

One other thing that I forgot to mention.. Don't know if you guys are familiar with it, but I had that radiant barrier stuff sprayed in just before the new ductwork & AH were installed. It's supposed to help and the demonstration that they do is really impressive. Now that I think about it, I'm kinda worried. Sure, the stuff might do a great job of keeping heat out of the attic for a little while longer. But what if it keeps the heat IN the attic longer too?

[Mr Bill]

Originally posted by wdj03

I do have an opening into the attic above my furnace & inside unit. And yes, it does seem pretty warm inside and around my closet. I would like to insulate it, but I thought that it's required to be open to the attic since I have a gas furnace.



And "do not" close that up that is were you get your combustion air from.

[wdj03]

Ok.. Problem discovered.. I had a tech come out & check it.

Turns out my condensor coil is almost dead. The guy touched it with his screwdriver and parts of the fins were falling off. He said to not even wash it or it will fall apart.

Now.. On to the next decision, what to upgrade with. I'll start another thread..

Thanks for the help here!

[iamrichard]

Originally posted by bornriding
FRom my experience being in the south ( S. Bama ) - If the unit is a 3 ton, then you are undersized.
I the unit is 3.5 ton, then yu have other issues, but ones that a good tech should discover.
At 1850 sg ft, without much humidity, you are pushing the very limits of a 3 ton system, with the insulation you stated, and the age of the home.

Richard

I agree with the hypothesis that the system may be undersized. If the unit is as old as the house it is time to upgrade.

Richard also

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