Check my logic here (HVAC)

[Aerovette]

Upstairs AC. I installed a NEST thermostat so I can have my privacy invaded. Each morning, I check the history for the day before. In eco mode, It runs about 14 hours a day. In non-eco mode, it runs about 17 hours a day.

It reaches temperature (75) and cycles off. The time it is off is fairly short, but it DOES cycle off.

My logic says this is more of a poor insulation/air leak issue, than a unit performance issue. If the 75 degrees can't stay in the house for any length of time, I have air leaks.

Agree?

If I set the temperature lower than 75, it seems to take FOREVER to get there and it won't do it when it is at the hottest part of the day (98 yesterday and will be 100 today) That says it is a unit issue. BUT...

We have an office at work that will not stay cool. It is located where an air return is. This made me start thinking. The hottest rooms in the house are located right at the return. The rooms away from the return are always noticeably cooler.

Is it possible that the cool air entering those rooms is immediately being sucked back in to the return vent and not actually cooling the rooms? That's what it seems is happening. It seems more than coincidental that the hardest rooms to keep cool are exactly where the return vent is. ALSO, that is where the t-stats are located.

What say ye?

[Rikki Z-06]

Originally Posted by aerovette

Upstairs AC. I installed a NEST thermostat so I can have my privacy invaded. Each morning, I check the history for the day before. In eco mode, It runs about 14 hours a day. In non-eco mode, it runs about 17 hours a day.

It reaches temperature (75) and cycles off. The time it is off is fairly short, but it DOES cycle off.

My logic says this is more of a poor insulation/air leak issue, than a unit performance issue. If the 75 degrees can't stay in the house for any length of time, I have air leaks.

Agree?

If I set the temperature lower than 75, it seems to take FOREVER to get there and it won't do it when it is at the hottest part of the day (98 yesterday and will be 100 today) That says it is a unit issue. BUT...

We have an office at work that will not stay cool. It is located where an air return is. This made me start thinking. The hottest rooms in the house are located right at the return. The rooms away from the return are always noticeably cooler.

Is it possible that the cool air entering those rooms is immediately being sucked back in to the return vent and not actually cooling the rooms? That's what it seems is happening. It seems more than coincidental that the hardest rooms to keep cool are exactly where the return vent is. ALSO, that is where the t-stats are located.

What say ye?

Burn it down and collect the insurance. YW

[GTOguy]

If you hadn't chased Yadkin off, he could have helped you with this.

[Rikki Z-06]

Originally Posted by GTOKareNNN

If you hadn't chased Yadkin off, he could have helped you with this.

STFU about him already

[dvarapala]

Originally Posted by GTOKareNNN

If you hadn't chased Yadkin off, he could have helped you with this.

Originally Posted by Rikki Z-06

STFU about him already

It's the truth.

If CHAS were still here OP could have asked him too.

[ThePirate]

You need a variable speed AC.

[Aerovette]

Originally Posted by ThePirate

You need a variable speed AC.

'Splain me please.

[Aerovette]

Originally Posted by GTOKareNNN

If you hadn't chased Yadkin off, he could have helped you with this.

Don't care.

[mrvette]

Vents for upstairs should be limited somewhat, and if possible get an attic vent fan to take out the hot air......my folks house evened out a LOT with the attic vent fan.....

my house here in Floriduh is one story/slab and the HVAC unit is in the garage, next to the kitchen then LR then hallway to BRs, and the 300' room addition....room addition has a white metal roof.....and a mainly non functional ceiling return....main return is near kitchen floor, with one more near the LR floor house is the same temp all over.....

[StaticCling]

Mr.Vette is technically minded, ask him?

[Bill]

The simple answer is, you're pushing the limits of what your A/C can do. Yes, the more well insulated your house is, the better, and shade trees are definitely a help, especially if they block the sun on your roof on the west side of the house. Having said all that, your A/C is only going to cool the air so much. If you're running it so that it virtually never shuts off, you're just riding that Pony Express horse to exhaustion, and sooner or later you are going to kill your A/C. I'd suggest just adjusting yourself to the season, keep it set at 80-82 during the day when you aren't home, and bump that A/C to 78, maybe 79, when you arrive home, and use ceiling fans. Maybe bump the temperature down a bit at night, after the Sun has gone down if that helps you sleep at night.

When it's 100 outside and you're trying to force 75 inside the house, unless your house is super insulated, of course that A/C is going to struggle.

The best bang for the buck, I think, is improving attic insulation, adding a radiant barrier, maybe even solar roof fans, but of course, all this isn't really practical to do right now. You have to do that when it's cool outside.

One thing you can do now is clean your A/C coils. Do it early in the morning. Shut them off, spray coil cleaner on the coils, let is sit, then use your garden hose to clean them off. If you haven't done that in a while that will help the units function better, as they can throw off more heat with clean fins.

[MadInNc]

Originally Posted by GTOKareNNN

If you hadn't chased Yadkin off, he could have helped you with this.

Helped ya **** it up ya mean

[04 commemorative]

When we go to bed,whatever I have thermostat set on I set thr fan to run for 12 hours,this way when AC cycles off the cool air is being distributed through out the house....I think this works better ..... I also do that during the day if it is really hot too.

[DAB]

could be any of the following:

poor insulation
air leakage/infiltration
wrong sized unit
wrong sized ducting
poorly laid out ducting/registers and vents
low on refrigerant
dirty coils (inside and out)
too much sun from window blinds being open


and probably a few more smaller things i can't think of.

homes rarely have properly engineered HVAC systems. they just SWAG it and hope for the best.

[GTOguy]

Originally Posted by bill_daniels

The simple answer is, you're pushing the limits of what your A/C can do. Yes, the more well insulated your house is, the better, and shade trees are definitely a help, especially if they block the sun on your roof on the west side of the house. Having said all that, your A/C is only going to cool the air so much. If you're running it so that it virtually never shuts off, you're just riding that Pony Express horse to exhaustion, and sooner or later you are going to kill your A/C. I'd suggest just adjusting yourself to the season, keep it set at 80-82 during the day when you aren't home, and bump that A/C to 78, maybe 79, when you arrive home, and use ceiling fans. Maybe bump the temperature down a bit at night, after the Sun has gone down if that helps you sleep at night.

When it's 100 outside and you're trying to force 75 inside the house, unless your house is super insulated, of course that A/C is going to struggle.

The best bang for the buck, I think, is improving attic insulation, adding a radiant barrier, maybe even solar roof fans, but of course, all this isn't really practical to do right now. You have to do that when it's cool outside.

One thing you can do now is clean your A/C coils. Do it early in the morning. Shut them off, spray coil cleaner on the coils, let is sit, then use your garden hose to clean them off. If you haven't done that in a while that will help the units function better, as they can throw off more heat with clean fins.

THIS^^^. It gets super hot all summer where I am. I have a one story house on a slab with a lot of tile and decent shade, but not a lot. I use the whole house fan in the AM and pull cool air into the house and shut all the windows by 8am when the temps get up to about 75. My AC is an in-garage unit (house is 2200SF) and doesn't even kick on until about 3PM on a 95-100 degree day. It is set at 80 degrees. With my electricity costing 39 cents per KWH, no WAY could I afford to keep my house at 75 during the summer. I use ceiling fans in every room to move air. As long as the air has a little movement, it's totally comfortable. But, I have very low humidity here, too, and that is a factor. My house is all dual pane glass and is very well insulated. Getting the hot air out of the attic in the evening at bedtime and in the morning is a huge help.

[RHunt]

Originally Posted by DAB

could be any of the following:

poor insulation
air leakage/infiltration
wrong sized unit
wrong sized ducting
poorly laid out ducting/registers and vents
low on refrigerant
dirty coils (inside and out)
too much sun from window blinds being open


and probably a few more smaller things i can't think of.

homes rarely have properly engineered HVAC systems. they just SWAG it and hope for the best.

yup.
remember - hot air rises and cool air sinks.
this is a common problem with 2 story homes.
And yes, most houses leak air.

I would make sure the A/C unit puts out the right amount of cool air and then revisit the ducting to have the intake where the warmest air is.

[Aerovette]

Originally Posted by RHunt

yup.
remember - hot air rises and cool air sinks.
this is a common problem with 2 story homes.
And yes, most houses leak air.

I would make sure the A/C unit puts out the right amount of cool air and then revisit the ducting to have the intake where the warmest air is.

As my original post says, I suspect the warmest rooms are warmest BECAUSE that's where the returns are.

Air exiting the ducts is measuring about 65 - 67 degrees.

[Rodnok1]

Don't forget sun load from windows, not only quality of windows but just the heat. We always close blinds on sunny side during summer and it helps immensely. I need to get heavier curtains actually.

[RHunt]

Originally Posted by aerovette

As my original post says, I suspect the warmest rooms are warmest BECAUSE that's where the returns are.

Air exiting the ducts is measuring about 65 - 67 degrees.

maybe split the returns to more rooms?

[RHunt]

I think the best cure is a 2 zone system.