How to cool house to lower temps?

August 31, 2025, 08:39 AM

I added insulation to my parents attic one summer, and you could tell the difference almost immediately. It was a weekend project. I installed attic vent chutes, and purchased a number of bags of blown-in insulation. Because I purchased so many bags the machine to use was free. I had my mom feed the machine while I was in the attic. It took less than an hour and we were done. The most time consuming part was the prep.

August 31, 2025, 08:48 AM

RogueJSK

Similarly, depending on what insulation you already have in your walls, you can sometimes blow additional insulation into your walls. This is done by using a hole saw to cut holes in the drywall at the top of each stud bay, then using a blower and hose to add in additional cellulose insulation, and you then just have to patch and repaint the holes in the walls. Not prohibitively expensive.

OP, if you haven't already, it may be worth contacting your electric company. I don't know about your area, but around here, the electric companies offer free home efficiency surveys. A contractor comes out and inspects your home, and then provides recommendations about things you can do to improve your energy efficiency and HVAC efficiency. This often involves free/grant-subsidized costs for implementing those recommendations too.

This is generally simpler stuff along the lines of recaulking windows, sealing gaps around doors, adding attic insulation, planting trees, retaping ducts, etc. (You're not going to get a free HVAC unit out of it.)

At my last house, I got free blown-in attic insulation and some free trees for the west side of my house out of this program. I also replaced the weather stripping around the front and garage doors, based on their recommendation.

August 31, 2025, 01:01 PM

9mmepiphany

quote:
Originally posted by RogueJSK:
OP, if you haven't already, it may be worth contacting your electric company. I don't know about your area, but around here, the electric companies offer free home efficiency surveys. A contractor comes out and inspects your home, and then provides recommendations about things you can do to improve your energy efficiency and HVAC efficiency. This often involves free/grant-subsidized costs for implementing those recommendations too.

This is an excellent idea...I can't believe it wasn't the first thing to came to mind

August 31, 2025, 01:13 PM

konata88

Is there a test I can do that would suggest whether not more insulation in the walls (not sure if possible since there is already insulation there - styrofoam?) or attic (blown to the right depth but I think the pink layers would be better based on my friends house)?

The thermal capacitance is already at a certain level which will just heat up the house regardless of outside temp (every wall, furniture, surface I measure is the same temp). Do I pick a day when the outside is hot (say 100 degrees), turn off the AC which is trying to maintain interior temp at the thermal inertia level (let's say 80 degrees) and see how fast the internal temp rises (thermometer) in a south / west facing room (with blinds closed)? Or what's a good, simple test I can do?

More insulation is probably better, at least conceptually. Just wondering how to figure out if there will be a pragmatic difference.

I think my AC is undersized too (13 seer, 3T?) for a ~30,000 cubic foot house (note, I think the air here is relatively low humidity - nothing like what it would be on the east coast).... Others in the area seem to have about 5T+ for similar volume house. Even still, their AC is running all the time too (they have a lower set point but not sure it matters - it may only be cooling down to the differential).

August 31, 2025, 01:20 PM

konata88

quote:
Originally posted by RogueJSK:
Similarly, depending on what insulation you already have in your walls, you can sometimes blow additional insulation into your walls. This is done by using a hole saw to cut holes in the drywall at the top of each stud bay, then using a blower and hose to add in additional cellulose insulation, and you then just have to patch and repaint the holes in the walls. Not prohibitively expensive.

OP, if you haven't already, it may be worth contacting your electric company. I don't know about your area, but around here, the electric companies offer free home efficiency surveys. A contractor comes out and inspects your home, and then provides recommendations about things you can do to improve your energy efficiency and HVAC efficiency. This often involves free/grant-subsidized costs for implementing those recommendations too.

This is generally simpler stuff along the lines of recaulking windows, sealing gaps around doors, adding attic insulation, planting trees, retaping ducts, etc. (You're not going to get a free HVAC unit out of it.)

At my last house, I got free blown-in attic insulation and some free trees for the west side of my house out of this program. I also replaced the weather stripping around the front and garage doors, based on their recommendation.

I'll look into it but not hopeful - our utility company sucks.

I wonder how much it would help, if additional insulation could be added, if we focused on just the south and west facing walls. Or would we need to do the whole house to be effective. Don't want to spend too much - hope to be out of here someday.

I see that there is some spray foam insulation that can be applied to the interior of the roof. Instead of adding more to the ceiling (floor of the attic), would it be better to add insulation to the roof interior? It's just plywood right now (and then whatever is on the exterior roof side, including the tiles).

August 31, 2025, 01:22 PM

P250UA5

quote:
Originally posted by ptruck:
I added insulation to my parents attic one summer, and you could tell the difference almost immediately. It was a weekend project. I installed attic vent chutes, and purchased a number of bags of blown-in insulation. Because I purchased so many bags the machine to use was free. I had my mom feed the machine while I was in the attic. It took less than an hour and we were done. The most time consuming part was the prep.

This is what I need to do. Maybe in the fall/winter. Put in soffit guards, radiant barrier & add more blown in insulation.

The radiant barrier looks to be the hardest, just getting to the top without falling through the ceiling

August 31, 2025, 01:25 PM

thumperfbc

Konata, I believe we are in the same region and suffer the same general climate. About 8 years ago we had our HVAC replaced. When the guy was working up the estimate they went room by room and checked airflow and temps and all sorts of things. They asked about any complaints we had with the current system. My chief complaint with the system then was the upstairs never really got cool even if downstairs was more than cool enough in the middle of summer.

The fellow looked around and then realized what the problem was: There was no air return in the upstairs space. None at all. There was a single air return in the entryway of the home (convenient location to the unit itself).

He explained there was no real way for the hot air upstairs to make it into the system efficiently and without that, it would never cool well. They redid the plenum box (or whatever it is called) to add a second return to the upstairs area and it made a huge difference.

Maybe it isn't relevant to your home, but it sure was to mine. I can easily maintain temps as low as I've tried (68) all summer long.

August 31, 2025, 01:38 PM

cparktd

I have 2 huge Holly bushes, one on each side of my 5 ton unit… but not so they block the airflow… just shade it. The sun never hits the unit and I have convinced myself that helps.
2600 foot house, one floor ranch. I can dial up any temp I wAnt winter or summer and hold it unless we have 20 guest and cooking as in a family holiday meal in warm weather… then it gets a few degrees behind.

August 31, 2025, 02:01 PM

konata88

Thumper - thanks. That makes sense. I have a single story.

August 31, 2025, 04:03 PM

jljones

The spray on foam insulation in the attic is the way to go. It is pricy. But an old house will see more retention of heat/cooling with the addition of spray foam insulation in the attic and new windows.

We saw a drastic change in heating and cooling with it. We started ripping out interior walls and adding insulation and have rooms that I can darn near heat with a candle.

August 31, 2025, 04:12 PM

4MUL8R

The differential temp is not from outside but from the return air temperature.

August 31, 2025, 04:30 PM

RogueJSK

quote:
Originally posted by jljones:
We started ripping out interior walls and adding insulation and have rooms that I can darn near heat with a candle.

Insulating interior walls also deadens sound.

Not something I'd necessarily do to your house all by itself, but if you're ever in a situation where you're going to be opening up the walls anyway, might as well put insulation in there before closing it back up again.

I did that with rockwool insulation in the master bathroom at my last house, during a bathroom remodel. It not only helped keep the bathroom toasty warm during winters, it also meant that someone could take a shower while another person slept in the adjoining master bedroom without disturbing them with the splashing and thumping.

August 31, 2025, 04:53 PM

konata88

Sorry for the dumb question, still trying to understand what to expect. If differential is between outlet and return vents (say 15 degrees), is this regardless of outside temp? What if the outside temp was 60 degrees vs 100 degrees?

I need to measure again but I thought the outlet temp gets cooler if the outside temp is also cooler. If so, then how does outside temp affect the differential, if at all?

August 31, 2025, 06:00 PM

Skins2881

This has been my confusion, you are discussing ∆T and outside temperature. They are unrelated.

Let's say your RA temp is 80° and your SA temp is 65°, eventually your RA temps will fall, lowing your SA temp continuously until you set point for room temp is satisfied.

The only relationship the outside temperature would play into things is if your house is poorly insulated or the system is not large enough to reject more heat that infiltrates from outside.

September 01, 2025, 09:08 AM

mrvmax

I have poor insulation in the walls and attic, single pane windows from the 80’s and a 23 year old unit. I can easily get to 70 degrees with outside temps of 95.

My utility bill is only about $350 in the middle of summer in South Texas. I have gas heat so in the winter it is about $100 for gas and $30-$40 for electricity. If I were to replace my windows (I have a lot of them) and insulate, it would take a while to recoup my investment. It might lower my bill by $100 or $150. I am happy with paying $350 in the summer and $100 in the winter.

I’d calculate savings before investing and also decide if you are staying there long term or not. If you plan on living there for a while, it may be worth investing. Most people do not stay in the same house for long.

Window units are pretty cheap, you could consider one to supplement. I picked up a 12k BTU 120v unit for less that $200 at the home despot. I only keep it on hand for when my main unit goes out. It will cool off enough to get me by for a few days. I am replacing my entire system this fall since I am sure it is going to fail due to age.

September 01, 2025, 09:50 AM

rangeme101

Great information given by all. Sounds like you need an AC check up. You could be low on refrigerant. Outside coils could be dirty. Poor insulation. Evaporator coil might need cleaning. Are you replacing your filter/s on a regular basis? Dirty filters will reduce the results of the unit. I replace monthly. Diff temp from return vent to supply vent should be 15-20 degrees. If not then your system needs to be checked. You could have a leak in any of the ducting to the supply or returns. This would suck hot attic air into your system reducing efficiency. If your house is insulated properly and it's 100+ outside you should still get the 15-20 temp diff inside. Now you might not be able to get your house below 75 inside but your vent diffs should always be that 15-20 degrees diff. Have your system checked by a trustworthy and reliable HVAC expert. I worked warranty for a major home builder in Houston TX 2005-2011. Every summer this was a constant homeowner call for AC not cooling. Most homeowners have no idea how a HVAC system works or its ability to cool. If it's +/- 100 outside with high humidity your house isn't going to be 65 inside with a typical residential unit in a cookie cutter house.

September 01, 2025, 01:26 PM

9mmepiphany

quote:
Originally posted by rangeme101:
Great information given by all. Sounds like you need an AC check up. You could be low on refrigerant. Outside coils could be dirty. Poor insulation. Evaporator coil might need cleaning. Are you replacing your filter/s on a regular basis?

That would have been my first suspicion and should be a regular maintenance thing

quote:
Dirty filters will reduce the results of the unit. I replace monthly.

This makes an amazing amount of difference.

I replaced mine when it started heating up (I'm not thrilled about going up the ladder without a spotter) and the difference was immediately noticeable...also vacuum out the grating

quote:
Have your system checked by a trustworthy and reliable HVAC expert. I worked warranty for a major home builder in Houston TX 2005-2011. Every summer this was a constant homeowner call for AC not cooling. Most homeowners have no idea how a HVAC system works or its ability to cool.

It's pretty funny when folks turn off their AC when they leave the house in the morning and complain that their AC isn't working when they turn it on when they come home.

Somehow the concept of their turning the inside of their house into an over escapes them, as does the fact that their walls and furniture will continue to radiate heat until they get cooled down.

My house is insulated enough to generally maintain a 20 degree difference with the outside temps. In the summer, you need to take into consideration that the sun coming through your unshaded windows treats the inside of your house just like sun coming through your windshield heats up the inside of you car

September 01, 2025, 01:55 PM

trapper189

A side benefit of the spray foam insulation is it keeps your attic cooler which keeps your ductwork cooler if it’s running through the attic and more conditioned air actually reaches the inside of the house.

September 01, 2025, 04:05 PM

rangeme101

You can also inquire about and do if found necessary, an air balance. Each vent should have a certain amount of cfm flow. HVAC tech can test each vent and if needed install, if you don't already have, baffles that can be adjusted for cfm flow at each vent. I know in a new house build that info is part of the HVAC design. So it's easy to know what each vent should have. Worth an inquiry. I had several houses adjusted for rooms that were too cold or hot than others. Or rooms in the sun or shade will need different flow.

September 01, 2025, 04:21 PM

Sacramento Johnson

Hi,
Living in southern Nevada, keeping the one's house cool is a major concern during the 6 months long summer we have!
I did a few things to help my AC and keep my electric bill from being overwhelming.
I don't really have any humidity to deal with, so your situation may be different.

1. Added a large attic fan that runs continuously all summer, pumping out the heat up there. (Our night time lows are still in the 90s for the entire summer.)
2. Ceiling fans in all rooms that run day and night.
3. Shade trees; the water to keep them alive is still cheaper than electricity.
4. Closing off rooms and their ac vents that are not in use, along with closets.
5. New duct work with better insulation and a second air return vent to help keep air flow over the ac. (Get the ducts cleaned regularly as well).)
6. Plastic shutters or shades over every window and heavy light blocking curtains in bedrooms in addition.