I've noticed this in a few houses I've lived in, some worse than others.

I tend to attribute it to the vehicles in the garage cooling off and radiating heat into the house.

Sometimes I'm not so sure though, the house heats up oddly after dusk with no sunlight and no running boiler.

Solar radiation bouncing around or some shit?

Humidity change?

Is it brick? Concrete? good heat sink material?

Are you turning on more lights (tiny heaters) after the sun goes down?

Is it a perceived change when you walk from inside to outside or vice versa? Or is it an actual change in the inside temperature on the thermostat?

Ooh nice. My area is very dry usually but it can swing around a bit.

The humidity, that is...

Otto, no, it's a robust insulated wood frame on a big ole concrete slab. 80's vintage.

The temp spikes a few to several degrees. All of my lights are LEDs so not a lot of self-heating.

Good thoughts though, I didn't think of the house as a heat sink, but that makes sense. Just not sure where the heat is coming from.

I live in an adobe brick home and the brick heats up during the day and then radiates part if the heat back into the house at night.

The walls are very warm to the touch during July, August and September.

quote:

Originally posted by DoctorSolo:
Ooh nice. My area is very dry usually but it can swing around a bit.

The humidity, that is...

Otto, no, it's a robust insulated wood frame on a big ole concrete slab. 80's vintage.

The temp spikes a few to several degrees. All of my lights are LEDs so not a lot of self-heating.

Good thoughts though, I didn't think of the house as a heat sink, but that makes sense. Just not sure where the heat is coming from.

My house in Florida did this and it was very noticeable.

AC was never shut off or anything but once the sun went down you could feel at least 1 foot away strong heat radiating from the bricks, especially on the West side of the house.

This was outside obviously but the heat would have certainly been radiating inside as well. I'd imagine anyway.

Not sure of the science behind it but once the sun stopped shining the absorbed heat would be released to the cooler surrounding air.

Interesting! Mebbe the foundation is soaking heat during the day.

It's a weird thing.

Interesting that you mention this because I just noticed the same phenomenon a few weeks ago.

My A/C has been out the last few years and I just made do with a large floor fan.

A few weeks ago I had the A/C repaired, turned out a breaker on the roof mounted A/C had tripped. While I was talking to the repair tech I pointed out that the digital thermostat face plate had a tendency to make/ break contact simply by applying light pressure to it, and it often tripped on its own simply by vibration, with the A/C and fan kicking on/off several times a minute, and he felt that might contribute to the breaker tripping so I ended up getting a new thermostat as well. He advised me to leave the fan in the "ON" setting rather than the "AUTO" one.

I don't need it super cool and set room temp at 77 F. and that worked perfectly for me...until about 7 pm or so, when I started to feel like it got a few degrees warmer. The fan was still running, so my first thought was that the A/C had quit again...but I blew it off thinking perhaps it was just my "internal" thermostat. But the same phenomenon happened every evening about the same time. I'd check the thermostat and it still read 77 F... I have a roof mounted AC, tall ceilings, a significant western exposure, live in a stucco structure, and don't have a garage...so I've pretty much settled on the possibilities that A) I'm feeling a humidity change once the sun goes down or B) perhaps some sort of heat sync is radiating heat near the A/C...that's the best I got.

We have a sun room that takes in a lot of solar heat before sunset and bleeds it out a bit to the nearby rooms.
My bedroom also butts up against the attic of the garage on the south side of the house. The garage is on a delay. It will stay cool into the afternoon like it is on a 3 hr. delay, but then stays pretty hot well after sunset unless it is opened.

I wonder whether this is a measured phenomenon, or a perceived increase?

In the absence of data (for example, hourly thermometer readings with HVAC systems disabled) one hypothesis is that maybe where you are, temps may suddenly drop at sunset, and that may be the source of this. Reason being heat capacity and human perception are funny things.

Imagine a massive object that is just slightly cooler than the outdoors is, when it's hot out. You're not going to feel any warmth coming from it because everything else is warmer, and you're getting blasted from the environment.

Now cool the environment suddenly. Now, that high-thermal-capacity-just-cooler-than-high-noon object - at the same temp as before - compared to everything else is the warmest thing out there, so you'd feel warmth radiating from it because everything else got colder. It's the same object doing its same heat radiation at the same temperature - but now it's the hottest thing out there and that'd make it noticable.

Anyway, that's one scenario to consider.

I read somewhere that 5pm or so is the hottest time of the day,

so it makes sense that any structure will hold heat and radiate it off for a time after the ambient temp has dropped,

my garage, insulated , not hvac, will peak in the mid 80's in the evening (sun sets on that side of the house, and a paved driveway)

it will still be warm inside vs the ambient temp outside sometimes the next morning

quote:

Originally posted by OttoSig:
My house in Florida did this and it was very noticeable.

AC was never shut off or anything but once the sun went down you could feel at least 1 foot away strong heat radiating from the bricks, especially on the West side of the house.

This was outside obviously but the heat would have certainly been radiating inside as well. I'd imagine anyway.

Not sure of the science behind it but once the sun stopped shining the absorbed heat would be released to the cooler surrounding air.

Would agree 100%. I spend most days at home and particularly my bedroom which is on the west side of the house. Since being more house bound I've noticed this phenomenon just as the sun sets, it stays cooking. My weather thermometer on the wall will get up to 89º whereas at the a/c thermometer will read 77º. It will stay this warm and the concrete walls warm to the touch for a few hours....thank goodness for the cooler months

Similar, our bedroom is on the west wall, you can feel the heat off the block walls in the late afternoon, especially in the summer where temps get up in the high 90's.

We're looking at upgrading windows in the house from single pane to more efficient units this winter.

Mine doesn't get warmer since I'm running the AC, but depending on the high temp for the day the AC runs more consistently between 1700 and 2200 even while the outdoor temperature drops.

Peak daytime heating usually occurs around 1600-1700 where I'm located, and the AC runs that additional time dissipating the thermal energy accumulated over the course of the day around the foundation/walls and in the attic. Just my .02...

My stats for yesterday:

Not our place.

When the sun is actually out we get a lot of afternoon and evening exposure and the house is always the warmest as the sun drops over the horizon. But up here in the PNW, the house invariably begins to cool down when the sun is down; sometimes quite slowly, other times more quickly, all of it pretty much depending upon the prevailing winds/breezes or lack thereof. The fact that our place can be somewhat drafty likely contributes in keeping any internal radiant heat that may have built up during the day from increasing the internal temps as it releases into the house at night as well, at least during the warm months.