Why is my house so difficult to cool? HVAC suggestions needed!

In My Humble Opinion
1

Our air conditioning situation is frustrating, and I don’t know what I can do about it. Maybe the other 10,000 brightest minds (and the few “total dipsticks” as Cecil calls them) on the planet can shed some light on what I might do differently.

We bought our house here in Euless, Texas, about four years ago. It’s a 1,969 square foot single-level single-family dwelling, with brick veneer over most of the outside. It’s about 10 years old now. The previous owners paid for one year of home warranty coverage, and a good thing, too, as in the first year, our air conditioner died, and we had the outside unit replaced under the warranty. So, it’s not the newest house, but the AC unit is in good shape.

Our neighborhood has many houses built on our floorplan or a mirror image of it. In fact, two of our friendliest neighbors have the exact same floorplan as ours. During a neighborhood discussion the other day, I griped about our high electric bills, and they were astonished at how much we were spending. This summer has thankfully been pretty mild (mostly 90’s, with a few days at or near 100 degrees Fahrenheit), but our biggest bill has been $246 – about $100 more than our neighbor across the street with the same floorplan.

In a worse season, say last summer, we had electric bills of nearly $500 per month, most of which was the result of our air conditioning unit running non-stop. We realized the futility of trying to keep the house at 78 degrees all the time, and have this summer learned to live at 80, 82, or even 84 degrees on the hottest days. It’s not exactly comfortable, but it hasn’t killed any of us (two adults, one teenaged exchange student, two toddlers, and three rabbits).

We recently had an HVAC guy come and take a look. He couldn’t find anything actually broken, but he did perform the semi-annual maintenance on the outside unit – something that is fairly costly, not covered by warranty, and recommended strongly by the warranty company. This, he said, along with switching to a less dense filter for the house’s single air intake would improve our efficiency measurably, but now I’m not so sure. He tested the air coming out of the vents with an infrared thermometer, and it showed 65 degrees, but he didn’t test it until after the maintenance, which makes we wonder if there really was an improvement.

So that’s the setup. I’ve been noodling over the possibilities – I know there are lots of modern ways to make your home more energy efficient – but I’m still trying to figure out what I’m doing wrong that my neighbors with identical floorplans may to have picked up on. During our discussions, they couldn’t think of anything different that they were doing, so I’m coming to you. Things I’ve thought about include:
[ul][]Ductwork – It’s entirely possible that our ductwork may have developed tears or ruptures. I need to take a look in the rafters and see if maybe we’re not venting some of that 65 degree air off into the attic.[]Fan – I can hold my hand up to the vents when the AC is on and feel the cold air coming out, but it doesn’t seem to come rushing out as strongly as it might – almost like a gentle breath than the work of a machine somewhere. How does your fan do for you?[]Hi, Opal![]Solar Screens/Big Trees - We don’t like the way these alter the exterior of the house, but it occurred to me that both of our neighbors have big trees shading the large windows at the front of their houses, whereas we do not. We do have white vinyl blinds on all the windows, though, and in the summer, they are perpetually closed.[]Attic Fans – The idea of continually pushing the hot air out of our attic really appeals to me, but I have to wonder how much of a difference it would make. For the record, neither of my neighbors with the same floorplan have them.[]The Refrigerator – This may sound like a red herring, but my wife and I suppose that behind the AC, this ancient rumbling beast is the leading single source of electrical strain on our power supply. In addition, it generates heat as it attempts to cool its contents, and seems to run more frequently than it should. Maybe we’re due for a new one?[/ul]What else is out there that I may (must) have missed?

2

Have you checked your insulation? If your neighbors houses are insulated (wall and ceiling), and yours isn’t, then it could make a significant impact. Also, is your ductwork insulated as well? I can’t help but think that if your ducts are in your attic and not insulated, then it’s just cooling the attic.

Also, what kind of window coverings do the neighbors have? White blinds with little or no curtains are likely to let in not only light, but heat as well. I have heavy drapes (insulated) on a room which gets a lot of sun, especially afternoon sun, in a particular room at my house, and I can tell the difference when the drapes have been closed all day, and when they’ve been left open with only the white blinds in place. (Even with the blinds closed, it makes a difference to have the heavy insulated drapes.)

3

Shade trees could be making a big difference. There is a noticeable temperature differential between the back (North facing, and heavily shaded) and front (south facing and almost no shade) sides of my house. Probably a 3-4 degree difference.

4

We had an attic fan and AC in New Jersey, and it seemed to make a tremendous difference. It also let us not run the AC lots of times. In the Bay Area we don’t have AC, since we’d only need it a few days a year, and we don’t have an attic fan. When the house heats up, it takes a long time for it to cool off without one.

That clearly can’t be the source of your problem, though. How about your windows? Do your neighbors have double pane windows? The other suggestions here make sense also.

5

Insulate. Lots of it.

Solar-powered attic fans.

There could be something wrong in your ducts.

6

Tree shading does make a big difference. Without them the house literally bakes in direct sunlight.
The direct sun will actually warm walls enough that during the night hours the heat radiates out of the walls into the house.

You might also want to check out the insulation in your attic or even the color of your house. Lighter colors will reflect more sun than absorb it.

7

I totally agree about the importance of not letting the sunlight in. I was sitting in my front room the other day, with the A/C running at 73 degrees, and I was just BAKING. I could feel a tremendous difference in the temperature of the room when I was standing within the sunlight than when I stood outside of it. You might really want some heavy shades to help with that.

Also, I think insulation helps a lot too. My parents’ slab ranch (vinyl siding) was insulated 2 years ago and they say their electricity bills dropped greatly in the summer.

I share the same suspicion about the fridge as you do - I have the-world’s-largest-old-fridge in my kitchen and I am pretty sure if I trashed it for a smaller, more energy-efficient model, my bills would drop enough to pay for it within a year or two.

8

I would compare your duct airflow to your neighbors, if there is a difference then that is where I’d look.

Other then that, is your a/c unit located in the sun while your neighbor’s is in the shade?

9

psiekier - What color is your roof? Light roofs reflect instead of absorb the heat. Do you have attic and crawlspace vents, and are they open in the summer so the air can circulate? Do you have ceiling fans, and if you do, do you reverse the blade direction when the seasons change? You want to draw the warm air up istead of push it down.

Are your electric bills higher in the winter, too? Because that would tell you if it’s your A/C or your fridge. What about your water heater - if it’s old it’s likely to be using more juice than a modern one.

An energy consultant would be an interesting job. People could hire you to analyze the power usage in their homes and suggest ways it could be reduced.

StG

10

I’m in Texas, also and am always working on keeping the electric bills down
My house is 2150 sq f and the ac unit is a 3 ton. My house sounds similar to your including single story, brick veneer and a single air return.

It has been recommended to me to upgrade to a 4 or 4 1/2 ton unit (one ton for every 500 sq f.) and I was warned that an oversized unit would cool before removing the humidity, which would not be good.

Anyway, I added insulated windows instead of screens because the screens are unattrative to me and I thought the double panes would be a better investment, resale wise. I also had insulation added to the attic. If I don’t see some better numbers, I will consider having the walls checked for insulation and/or upgrading the unit to the larger tonnage.

11

Hey, neighbor.

I’m in a 1,700 sq. ft. in Bedford and my highest bills this summmer has been around $230.00.

I have made a couple of improvements this summer that should have helped, but with the rising rates, I don’t know if they have. I had the roof replaced and had them install a ridge vent. I installed eave vents to accompany them. I’ve had electric vent fans for some time, and I’ve notice that they don’t run as late into the evening now with the additional vents.

Here are some things that are contributing to my problems that I’ve not yet corrected. My master bedroom and living room face the southwest and there is little shade on that side. I can feel the heat radiating from the brick for several hours after dark. I’ve installed sun screens on those windows and the screens made a big difference, but some landscaping to keep the sun from heating those bricks would really help.

My A/C ductwork is mostly a plenum in the middle of the house. However, the master bedroom is fed via a flex duct that runs across half of the attic. The insulation on the flex duct keeps coming off. So master bedroom is never quite as cool as the rest of the house.

My A/C air handler is on the unused end of the house. The return air has to travel a circuitous path and down a hall. Originally, there was only one 12" x 24" return air louver. I added a second in the adjoining room and greatly increased the airflow across the coils. The A/C repair guy told me that insufficient airflow was the cause of my coils freezing up; there wasn’t enough warm air transferring heat to the coils. The extra return air vent helped that problem.

One A/C repair guy told me that some the super-duper allergy filters are very restrictive.

Another A/C guy told me that some builders are careless about the louvers on the vent covers. They tend to mash down when packed in the box by the manufacturer. He told me to take a pair of pliers and bend them out so that they are more open.

12

But the blinds are still on the inside, right? By the time sunlight has reached them it has already gone from short wave to long wave and remains inside as heat energy. How about some inexpensive shutters for the outside of the house?

I’m doing a full kitchen renovation and discovered several places where flexible ducting was pinched, and apparently when this building was converted back in the 80’s one duct was brought into the kitchen ceiling but never actually connected to the ceiling register - so it was just dumping all of its output into the ceiling joist area.

Since you say you just had a tune up, I suppose your condenser grill was checked for lint buildup?

How about checking wall surface temperature to see where warm air might be getting in? In the winter if you remove a wall switch or outlet cover plate, do you feel cold air rushing in?

13

Please answer a question;apart from the price of electricity,can the A/C cool the house to a suitable level?

14

All of the AC units are deployed similarly, sitting on a small concrete slab on the north sides of the houses. At varying times of the day, these units can be in the sun or in the shade, but none of us have taken extensive measures to shield them from the sun.

Our roof is dark, but not any darker than those of my neighbors. All three are virtually identical. We have attic vents, and, AFAIK, they are open, but I haven’t looked at them lately to see if there may be some kind of obstruction. Our house has two ceiling fans, and they are on perpetually.

Our electric bill is higher in the winter, but not by an inexplicably wide margin like in the summer; we’re talking about a $30-$40 difference in the winter vs. a $200-$300 difference in a bad summer (like last year).

All three of us have gas heaters (the fan is still electric) and gas water heaters as well, so they play less of a role in the electric bills and more in the gas bills during the winter.

Our new unit is a 4 ton. We don’t seem to have a problem with humidity. I know on really humid days (the ones where you go outside and your sweat doesn’t evaporate), we don’t feel any ill effects indoors.

We have a fairly thick layer of fluffy pink insulation in the attic, but to be honest, I don’t know how it stacks up against my neighbors’. We’ve never been in each others’ attics. We feel the same way about solar screens as you do; I seem to recall one of my neighbors having the solar screens on at least one side of his house. That might be a contributing factor.

AFAIK, our windows are nearly identical – all three of these houses were built by the same builder, on the same floorplan, at about the same time. They are for the most part double-pane glass, but we have some decorative windows that may be a problem in this regard.

Huh, sounds like we may be in the same boat.

We got the same recommendation from our guy, and switched to the cheap filter filled with fibrous blue material.

Are you talking about the vents under the eaves of the house? I may have to look at those; I’ve never checked that closely.

Checked and cleaned, Patty. I’m hoping that made a difference, but since the AC guy only checked the air temperature after the cleaning and not before, I have no basis for comparison.

I will certainly be getting this cleaning done more frequently now, that’s for sure.

On a reasonable day (i.e., it’s not 106 degrees outside), yes; we consider 78-80 degrees to be suitable. It bakes my brain, however, that my neighbor down the street with the same floorplan claims to be able to cool his house to 73 degrees on the same days with a much lower electric bill.

15

I think this is the problem. 65 degrees is pretty high. I’d expect 55 to 58 degrees for a refrigerated air system. Did he check the temperature of the air downstream of the DX coil in the air handler?

If the temperature of the air coming off of the coil in the air handler is 65 degrees, you have a problem with the AC system. If the air coming off of the coil is 55 degrees, then the air is picking up heat somewhere along the duct. Probably poor or missing duct insulation (and if you have flexible duct, I’ll bet this is the case). If this duct is in the attic, the problem is made worse if the attic ventilation is poor - an attic fan would help keep the attic cooler and result is less heat gained by the air in the duct.

How easy is it to inspect the duct? Flexible duct doesn’t hold up too well in an attic, the plastic starts to fall apart. Be careful inspecting it, I’ve had it fall aprt just by touching it.

If the duct is flexible duct, the best course of action is to replace it with rigid metal duct and properly insulate it (expensive though). Replacing it with new flexible pre-insualted duct would be cheaper and easier, and should last for several years before it deteriorates again.

Finally, I wonder how good the HVAC technician was if he thought a 65 degree discharge temperature was ok. It’s not, and he should have known that.

16

Have you checked the insulation in both the walls and the attic?

17

There has been some good suggestions, (and I think many would help) but the problem is in the A/C system.

First things first:
You mentioned a “basis for comparison.” Here’s some:

  1. Houses of your age will require one ton of cooling per 500-1000’ ft². The most common would be 700 sf² per ton. At 700 ft² per ton, your house should be around 2800 ft². (given that you told that you us have a 4 ton unit; 4x700= 2800) The better the windows, insulation, attic ventilation etc the more you can get. A well constructed house may get up to 1000 ft² per ton. A poorly constructed house as low as 500ft² per ton. Note Ca3799 has a 3 ton system serving 2100 ft²

What is your square footage [of living space served by this unit] ?

  1. I agree with Dag Otto that 65° is high. However we don’t know if that is a problem without knowing what the humidity and temperature of the house was when the tech read 65°. A correctly sized, and correctly installed and serviced unit will produce a 20° drop accross the coil. If the return air temperature was 85° then 65° was OK; particularly if the house was humid. So we [you] don’t know if the 65° is/was a problem unless we know/knew what the return ait temperature is/was, and the humidity. When the house is comfortable, the A/C system will produce a 20° drop from your “cold air return” to your supply registers. A typical reading would be 75° return air, 55° supply air, at 50% relative humidity. If you go out of town and turn the A/C system off, you will come home to high humidity and high temperatures. You may have 95° return air and 75° supply air; a 20° drop! But…as the house “recirculates” the air, the return air and supply air will both move down in lockstep. Make sense? So, take a thermometer and tell us:

What is the return air temperature, supply air temperature and relative humidity?

Other questions that will help us tell you what to look for:

  1. Brand of A/C? Model number?
  2. Programmable thermostat? Do you use it?
  3. Does this house sit on a slab? Is there ductwork in the attic?
  4. Do you run the fan continuously?
  5. Where is the thermostat located?
  6. What size furnace? (Btus)(and blower if you know it)
  7. Does this unit have a history of refrigerant leaks? Does it use R-22? (or 410A?)
  8. Is there ductwork in an attic? Is it insulated? Has it been inspected?

If you really want to get anal and find the problem call the service tech back and ask him to check out the system. Set the thermostat for 75° several hours before he arrives.

Ask him to record the following information, before and after. (Before being defined as before he makes any adjustments whatsoever)

  1. Static pressure test of condenser. This is a little uncommon but it will tell if there is air in the system. This will require: A) PSIg reading of condenser/system with system turned off. B) Accurate reading of outside air temperature at the time pressure was taken. (We’re looking for something called the “P/T relationship” of that refrigerant)
  2. Outside air temperature and humidity.
  3. Inside air temperature and humidity.
  4. Return air temperature at return air register.
  5. Return air temperature at the point of entering furnace.
    (The reading between item 4 and 5 should be no more than 1-2°. If #5 is higher it indicates that you are picking up heat through the return air ductwork; a sure sign of leaking or broken ductwork in an attic sucking in hot air.)
  6. Supply air temperature.
  7. Fan speed setting
  8. Suction pressure and head pressure
  9. Both superheat and subcooling
  10. Identify the type of metering device

Note that this information is not extraordinary. A professional tech harvests this information every single day. (with the exception of item one, that takes 90 seconds to perform) The point is, this is a garden variety service call and is part of a routine preventive maintenance call. It shouldn’t cost you any more than a basic PM call—$89 or so in my parts.

Anways…You haven’t given us enough information to diagnose this. However…my guess is that there is a problem with the A/C system. All of the other ideas are good—including your own. However they are not addressing the “root cause” of the problem. If you do this-----and I strongly suggest you spring for the $89***-----remember, before and after.

(*** look at your utility bill if you’re struggling with that)

18

Also…

A house that was 80-84° and the tech found no problems? 65° and that wasn’t an issue?

In every company there are varying levels of skills among techs. You might choose a different company—one of the larger ones with professional training. And ask for a journeyman—a skilled tech to come out.

You have a problem of some sort. Perhaps the tech didn’t have the experience to diagnose a problem that is out of the ordinary.

Just sayin…

19

The A/C guy told me what my problem was. A valve on the suction side of the compressor is failing and the suction pressure is too low. There’s not a solid column of fluid coming from the condensor back to the compressor. I’m just not yet ready to spring for a new one, yet. They’re required to install more efficient units now, so I’ll have to have the air handler replaced at the same time.

I was talking about the vent covers at the end of the duct; the ones going into your room. But, it wouldn’t hurt to check the ones outside also. You might check to see if they need cleaning, too.

20

That is an expansion valve and it located at the evaporator inlet. It can be replaced without replacing any of the coils, or system. It’s about $300 to replace.