Hvac doesnt run as much on an overcast day?

[Hobby_Man22]

It's still 95 outside even though it's cloudy, minus the sun beating down. This has me thinking I need more insulation on the roof. Currently have r30 would like to add another layer of r15 over the r30. I don't like how the ac runs constantly from 1-5pm. Sometimes it shuts off, but then kicks back on after 5 minutes

 

[Jim greengo]

Check your doors/windows also.
When was last time ac was serviced?

 

[BrandonV]

Where in Texas are you located and what is the thermostat set at? As the outdoor temperature reaches the design temperature of your system the unit is going to get closer to running continuously.

 

[The Cobbler]

sun gives a lot of solar gain , more so that air

 

[chinboys]

Borrow an infrared camera to highlight the area where the heat is being driven in via inadequate insulation or drafts.
Get a Manual J design calculation to verify your cooling tonnage.
Make sure your hvac system is working correctly... Refrigerant level and clean evaporator and condenser coils.
Correct the problems.
Realize with inadequate insulation, the heat transfer mechanism via radiation and conduction during the heat of the day means your air con system cannot keep up with the heat gain.
Set up a setback of 3 degrees on your thermostat. The system will run longer but also stay off longer.
Don't expect any system to have more than a 20 degree delta between outside and inside temperatures.

 

[Hobby_Man22]

Borrow an infrared camera to highlight the area where the heat is being driven in via inadequate insulation or drafts.
Get a Manual J design calculation to verify your cooling tonnage.
Make sure your hvac system is working correctly... Refrigerant level and clean evaporator and condenser coils.
Correct the problems.
Realize with inadequate insulation, the heat transfer mechanism via radiation and conduction during the heat of the day means your air con system cannot keep up with the heat gain.
Set up a setback of 3 degrees on your thermostat. The system will run longer but also stay off longer.
Don't expect any system to have more than a 20 degree delta between outside and inside temperatures.

It will hold 72 when it's 100 outside, but it's going to run the whole time. If you kick it up to like 77 it will shut off for a bit. Like 10 minutes off before it kicks back on for another 30 minutes or so.

 

[Sumboodie]

Not sure how you have insulation on aroof. Around here we usually do at least r48 in the ceiling.

No 95* though. Hit 62* today with sun (haven't seen that in weeks it seems) and I was sweaty.

 

[mike93lx]

It will hold 72 when it's 100 outside, but it's going to run the whole time. If you kick it up to like 77 it will shut off for a bit. Like 10 minutes off before it kicks back on for another 30 minutes or so.

Constantly running, but keeping the setpoint in the hottest day means it is sized perfectly. It's exactly what you want

 

[liliysdad]

Don't expect any system to have more than a 20 degree delta between outside and inside temperatures.

I’ve heard this my entire adult life…and it’s absolute nonsense. It was 112 here today. If my system couldn’t keep my house any cooler than 92, I would be pissed.

System runs damn near all day, but maintains a temp of 73-74 on the hottest days. I keep the thermostat on 70 during the hottest part of the day, 68 at night. I’d have a mini split in every room if I couldn’t do better than that.

 

[CraigStu]

I am not sure I understand your thinking of insulating the roof. Are you conditioning the attic as well as the living spaces? Not that it would hurt to add more roof insulation but I wonder if adding more insulation to the attic floor, and working to get more airflow through the attic might be easier.

 

[jar944]

Don't expect any system to have more than a 20 degree delta between outside and inside temperatures.

You mean 20 degree delta between incoming and outgoing air across the coil.

Not inside and outside air.

 

[DGersic]

Sun heats everything more. Look at your roof, what colour is it? If it’s dark, it heats up a lot. Look at your windows, too. They can let in a lot of heat along with the light. Walls, similar to roof, light colours heat up less than dark.

Insulation slows down the movement of heat.

 

[wssix99]

Reading about passive house design may give you some creative ways to fight solar gain for your particular house and location: https://en.wikipedia.org/wiki/Passive_solar_building_design

 

[racecougar]

Reading about passive house design may give you some creative ways to fight solar gain for your particular house and location: https://en.wikipedia.org/wiki/Passive_solar_building_design

It works quite well. My house was designed by a passive solar specialist architect. It's incredible how efficient the building is.

 

[dcg9381]

It's still 95 outside even though it's cloudy, minus the sun beating down. This has me thinking I need more insulation on the roof. Currently have r30 would like to add another layer of r15 over the r30. I don't like how the ac runs constantly from 1-5pm. Sometimes it shuts off, but then kicks back on after 5 minutes

In Texas, the roof insulation is a big deal. I assume you have an attic and insulation on the attic floor.
I assume your air handler is in the attic.

Adding spray foam to the roof deck will result in a substantial decrease in temperature in the attic, and then you have an air handler sitting in a space that is much cooler.

Adding more "attic floor" insulation isn't a bad idea, but it's not as effective as doing the roof deck due to the location where our air handlers are in Texas typically.

 

[CraigStu]

...Adding more "attic floor" insulation isn't a bad idea, but it's not as effective as doing the roof deck due to the location where our air handlers are in Texas typically.

Ah that does make sense. I didn't realize the AC in the attic was so common.

 

[mike93lx]

Ah that does make sense. I didn't realize the AC in the attic was so common.

Two of my three units are as well and it's hot as **** up there.

At least it's better than having a water heater over living space

 

[Hobby_Man22]

In Texas, the roof insulation is a big deal. I assume you have an attic and insulation on the attic floor.
I assume your air handler is in the attic.

Adding spray foam to the roof deck will result in a substantial decrease in temperature in the attic, and then you have an air handler sitting in a space that is much cooler.

Adding more "attic floor" insulation isn't a bad idea, but it's not as effective as doing the roof deck due to the location where our air handlers are in Texas typically.

You can't add insulation to the roof deck down here. Everyone who does that gets mold. Has to be in the rafters

 

[mike93lx]

You can't add insulation to the roof deck down here. Everyone who does that gets mold. Has to be in the rafters

If you insulate the attic, you need to condition the space and seal it. Doing that will prevent mold

 

[jar944]

You can't add insulation to the roof deck down here. Everyone who does that gets mold. Has to be in the rafters

You can do a hot deck roof in any climate. And even if you couldn't (you can) you could do vented/ air gapped assembly.

 

[dcg9381]

Two of my three units are as well and it's hot as **** up there.
At least it's better than having a water heater over living space

Oh, I've seen houses with both "features".

I think they started adding radiant barriers to roofs in early 2000s, which helped with attic temps, but the temperature in a Texas attic on a "traditionally insulated" home and a foam insulated home is easily 20 degrees or more. That's a lot of added "efficiency" for an air handler and duct-work that might be R-4 insulated at best.

You can't add insulation to the roof deck down here. Everyone who does that gets mold. Has to be in the rafters

Are we talking foam insulation? Maybe we're not talking about the same thing? It's better to cover the rafters in foam to prevent thermal bridging from the roof deck, but yea, modern homes in Texas the attic is sprayed to the roof deck.

Here's my living room (no attic) - sprayed directly to the roof deck. In the attic, rafters are covered. There are "perhaps" issues with foam insulation and moisture in northern climates, so you'll likely see humidity control systems up north. But here, we run our HVAC so much that it doesn't seem to be an issue.

This is my 3rd structure built like this. No mold or issues other than an energy bill that's below average. Steel shop has the same insulation.

You can do a hot deck roof in any climate. And even if you couldn't (you can) you could do vented/ air gapped assembly.

I just dealt with a structure (up north) that had an air gap assembly and foam insulation. Not a fan, but I'm also not that familiar with their insulation techniques and it may be 100% valid up north... Had they used OSB for the air gap, would have been fine.