Air Con Sizing

Danny30

Thanks for this, super helpful.

Just wanted to ask, you say your hallway is also cool, so I am assuming the the air con unit in the Lounge is getting through the door in that case? Does it cool the hallway and the bathroom down also when the air con in the master bedroom is not swithced on?

vic_sf49

I shall have to experiment.

The bedroom one is already being replaced next week, and has now developed a 2nd issue, so definitely a problem child.

Today it seemed to be calling for most of the refrigerant, and hogging it, so the lounge one was tepid.

I'll try just running the lounge one tomorrow. Although if the system is having issues, it might need to be switched off this week, which will make me cry!

I recommend you go with whatever brand, comes with free parts AND labour. ETA, luckily I did.

vic_sf49

I've not forgotten about this, but either it's not been working correctly, or has been, yet outside is much much cooler, so I'm not getting a true feel for where the cool air travels.

I was also previously running them on higher fan speeds, and at colder set temps, which I've learnt makes the room you're in, rather uncomfortably cold.

So that may be a factor you need to consider. Yes, you could run the one (was it) 18000 or 24000 btu unit, on full whack, to cool the other areas, but your lounge / dining area, might be baltic.

I'll see how the next few days pan out, as the temps warm up again.

Replacement is hopefully still scheduled for Thursday.

ComicGeek

There's a big difference between having an air con unit in one room to provide respite from the heat, and having the whole house evenly conditioned.

I always think of cooling as blowing up a balloon - you are physically pushing the heat away, and the air con system also has to keep pushing out cold air to keep the heat at bay. If you seal up the rest of the house (ie closing windows, closing curtains etc), then you are also helping to keep the heat outside, which means that the air con system can be more effective. Air con will never be effective with windows open and sunlight streaming into the house.

Install the air con in the hottest room, and then this heat doesn't migrate around the house.

vic_sf49

Great comment there from@ComicGeek , "install it in the hottest room, then this heat doesn't migrate around the house", which explains what I'm coming to realise.

I likely only need the bedroom one on in the morning, to counteract the heat from the morning sun.

Then run the lounge aircon from noon, to deal with the afternoon and evening sun.

And having them come on using the timer / schedule, so they're on just before it gets hot, and can run on a gentler setting, to maintain the current temperature, rather than massively needing to cool the place.

So I might end up running mine less, but more efficiently.

Tis all a learning curve. I had them fitted just before the first heatwave, so wasn't sure how they'd do, and probably over-egged the settings.

All this ^^ to be tested, on the upcoming 30 degree days.

jonnydeppiwish!

have you tried ceiling fans? Just installed mine and it’s a lot cheaper! Bought this one as wanted something that didn’t look like it was out of the 70s

https://ollyri.com/products/modern-faux-wood-6-speed-reverse-frequency-fan-light?variant=47196013690932

ComicGeek

Ceiling fans, closing curtains etc can work great when there are only a couple of hot days in a row. Delaying the build-up of heat in room until the cooler night/days arrives and you can purge ventilate.

But what do you do when there are multiple hot days in a row, and the night time temperature also doesn't drop much? Ceiling fans and tower fans can provide some relief, but the disruption to sleep and work is still there.

We have talked about increased global temperatures from climate change for decades now, and people are just starting to realise what this means - it's not a slow and steady small increase in daily temperatures, it's an increase in average temperatures with large increases in peak temperatures. Around 2.7k excess deaths in the UK in the last couple of months due to heatwaves - only around 1.6k road deaths in 2025, so perhaps we should be treating excess heat as seriously as road safety in this country now.

I saw some nonsense on Channel 4 news about using cold rocks in basements and chimneys to cool buildings in the UK - that might have been sufficient 10-15 years ago, but would never work today and will definitely not work in 10 years time.

stuart45

Never heard of the cold rock trick. I've heard of hanging wet cotton sheets at an open window to cool air as it enters the house, although it's more effective in a dry heat.

vic_sf49

Got it working today @Danny30, to give it a decent enough test. Not on as high a fan setting as 3 weeks ago, but high enough to feel where the airflow was.....

Blue = noticable cool airflow from the lounge aircon.

Red = door is open, but you can't feel the cool air from the lounge today. Feels warm compared to the lounge, as soon as you're 2 feet through that door.

Yellow = forgot to say I have a fan there, which I don't always realise is still on (solar panels, so it running at 2 watts, isn't going to bankrupt me.)

So I reckon it's the bedroom aircon + fan, that cools that hallway, and rooms off it. That aircon had been failing to stop cooling once at temp, so that very very cold air, was making itself known.

Bedroom was too cold to sit in however!

vic_sf49

Thanks for starting this post OP, as it's been a great experiment for me.

And to wrap this up, only the bedroom aircon is on.

Fan is not on. Lounge aircon is not on.

It is the bedroom one that's cooling the hallway, as I was stood outside the bathroom, and could feel the cool air.

Fan setting on aircon was set to 1 of [Quiet/1/2/3/4/5]

Airflow as follows....