Living-room ceiling height for a new build

[Riley'sLife]

At night, we propose to draw cooler air into a well insulated living-room from outside, while expelling the warmer air via a ceiling mounted whole-house fan at the same time

In the mornings, we hope to be able to keep the lower temperatures achieved in the room for as many hours as possible without using the aircon in that room at all, or at least not until it becomes absolutely necessary.

I am mind-juggling the benefits of a low ceiling when using aircon with the advantage of a room with high ceilings for keeping any warmer air stored above head height, against the cost of running aircon in a high ceiling room and the more rapid effect of heat building up in a low ceiling room.

Anyone know what the optimum ceiling height is for such a living-room in the Tropics? The room will be 32sq. metres.

[IMHO]

As you know, generally speaking the floor of a room is cool, and during the daytime at least the ceiling gets hot - even with the best of insulation. Higher ceilings keep that heat radiated from the ceiling further away from you, lower ceilings bring it closer..

There's no one easy answer though... As the ceiling gets higher, it gets even closer to the roof, making it hotter. I also increases the volume of air in the room for an AC to cool. There is a sweet spot there, but it needs to take all of this into consideration. the normal "standard' in Thailand is a ceiling height of 2.8-3.0M in rooms with a roof directly above, but that usually drops to around 2.5M for rooms with a floor above.

As for venting the room into the roof cavity - do not do this unless you have a lot of soffit ventilation. If you don't have a very well ventilated roof space, what can to happen is hot air will force it's way through the fan aperture and into the room as the air inside the roof heats and expands (assuming the fan isn't running, and can't seal off when it's not). On this front, even typical downlight fittings can "leak heat" into the room (as confirmed by my infrared thermometer).

Edited July 18, 2015 by IMHO

[Riley'sLife]

Yes, it’s that elusive “sweet spot” that I need to determine!!!

Just to clarify… the whole-house fan will feed into fully insulated ducting connected to a dedicated screened louvre at the gable-end of the Bali-style roof so that the expelled air will not enter the roof void, Other adjacent screened louvers will vent the roof void itself , as will the extensive soffit vents and all will be thermostatically fan assisted 24/7 to hopefully eliminate the possibility of condensation affecting the steel roof.

The house will be raised above ground level on either 1.4m or 2.4m high conc pillars (the "boss" didn't decide yet!) and will be on one level. The roof will be Off-white Colorbond with foil barrier on steel frames with suspended ceilings incorporating at least 150mm fiberglass insulation. The livingroom will have only one external wall -east facing with double or triple glazed French windows opening onto a balcony extending out just over 3m. The ceiling heights for other rooms which surround the livingroom to the south, west, and north (and will be used with aircon whenever they are used) will be 2,4m.

Your valued input is greatly appreciated. From other posts you have made on the forum relating to construction I can see you know what you are talking about.

[Pdaz]

I'd make the ceilings 3m as a minimum. It's not just about cooling. High ceiling give a feeling of openess and space. So much more appealing than low ceilings. I don't know how tall you are but I'm 193cm and a 2.4m ceiling seems very low to me. Also the standard 2m high thai door is rather old fashioned looking these days. High ceilings and " oversized doors" are much better imho

[jimmym40]

I totally agree with Pdaz comment above. 2.4 height ceiling is gravely too low. I've built and lived in 4 houses in the past 20 yrs here. I've always went with 3.0 height ceilings. Gives a much more pleasant atmosphere and openness. Also, since the room you are talking about is only exposed to one outside wall, I wouldn't be too concerned about the heat and keeping it cool. There's only several months out of the year that you really have that nice cool air that you can circulate. I really don't think you'll be saving a lot of money by using the fan system. Plus, how is that going to look in the middle (or somewhere) of the living room?

[oneday]

I would never set my ceiling height based on cooling unless you are poor and can't afford the electric bills.

I would concentrate on aesthetics. Too low a ceiling is going to feel claustrophobic. I like the standard ceiling heights in Thailand at about 2.8M.

[steven100]

yes , thailand standard ceiling in 2.8m which is considered low.

Go with 3.0m ceiling , it will be both visually pleasing and the room may cool quicker as the warmer air has more upper area to dissipate.

[technologybytes]

Its natural to assume that a high ceiling room will cost more to cool with aircon, but in my experience its not the case, as cool air falls and hot air rises you will find the the air above the level of the air conditioner can be warmer. I can demonstrate this in a high ceiling room with aircon on when its a hot day outside, if I climb a step ladder and put my had above the level of the air con on the other side of the room I can feel the warmer air above the level.

If you want a cool space, have higher ceilings. In my experience the higher the better.

Also, for best insulation do build cavity walls. I converted a room to cavity walls on the "hot side" recently and it made a tremendous difference, an added benefit is not having those ugly columns in the corners.

If I build a house in the future or if I renovate a old one I will certainly go with cavity walls.

Also, plenty of roof insulation and just as important, roof ventilation.

Edited July 20, 2015 by technologybytes

[SOUTHERNSTAR]

OP just like the ceiling height has an effect on temperature, the distance between the roof and the ceiling also has an effect. If its possible look at ways to increase the distance between the roof and the ceiling and get airflow going in this space by extracting hot air and allowing cooler (outside) air to flow in.

[fred Kubasa]

Recently I visited a friend's apartment in Hong Kong that seems to answer your query. He had an old apt. with 12 foot ceilings, he put in a false ceiling, ( 2 ft. acoustical tiles ), at 8 feet and installed 2 small exhaust fans ( like the bathroom ones), with a separate switch for those. The air con. goes on very briefly and the fans, at ceiling height, remove the hot air. He can then shut off air and fans until heat level rises. Claims he cut energy cost 50 % !

[jimmym40]

Ref "fred" above. I don't believe him, 50%. He just doesn't want to admit it wasn't a good idea.

[Psychic]

I have white insulated color bond, and except for the lack of wind it is as cool as the outside.

Also, my living room is nearly 4m versus 2.8m or so in the bedrooms and the living room is much cooler than the bedrooms.

I will probably vent the bedrooms to try and move the heat. Its not unbearable since the house was built with 20cm q-con but I am trying to avoid air-con as much as possible and on the hottest days they're still a little warm in the evenings.

It sounds like you're on the same line of thinking, so I'd recommend the higher ceilings.

[Gumballl]

My (wife's) single story home has 3.5 (perhaps 3.75) meter ceilings. We do not have a heat problem whatsoever. We do have vents (that are screened) in many places outside the roof overhang (awning), but nothing motorized circulating the air in the space between the tiled roof and the 'exterior' of the ceilings in the home.

[fang37]

Insulation is a combination of factors -

We have QCon -15 x 10cm - bigger the better

Quality roof tiles

Tinted windows

Aspect of house matters

Ceiling height - ? - 9'3"?

Exterior - garden - trees assist

We have A/C (Mitsu) in the living room & bedrooms.

In summer, we use A/C in the afternoon - fans at night - Fang.

It has been a successful recipe.

[passingas]

High ceilings do not cost more to cool with air-con, as cool air always falls, just as warm air always rises....ti's called physics. In our 4 story library at the University I teach at, the ground floor is always nice and almost....cool enough for a wanna be polar bear like myself. You go up to even the 2nd floor and you will notice a real temp difference. You will never, ever cool the higher reaches of a tall ceiling room, no matter how long you run your AC. So in essence....don't worry about it. Get it comfortable and then turn the AC either way down or off, altogether. I have 14' ceilings in my house, with no AC at the present. That may very well change here in the very near future, though. pg

[IMHO]

High ceilings do not cost more to cool with air-con

I'm sorry, but that's just not true.

Not only does more room volume cost more to cool, you also need a bigger AC to do the job.

OK sure, there's not much difference between 2.8 and 3.0M, but push it to 3.5M or more, and the spec for your AC just changed.

[Gumballl]

High ceilings do not cost more to cool with air-con

I'm sorry, but that's just not true.

Not only does more room volume cost more to cool, you also need a bigger AC to do the job.

OK sure, there's not much difference between 2.8 and 3.0M, but push it to 3.5M or more, and the spec for your AC just changed.

If a person has a single-story home, with 3.5m ceilings, and this person is no more than 2m tall, then what difference would it make at all if the air sitting above the 2m level is air-conditioned or not?

As mentioned earlier, cool air falls towards the ground, and hot air rises. Thus with a 10 sq-m room, regardless of whether it has a 2.5m or a 3.5 m ceiling, the effort to cool the 'habitable' zone of the room will remain the same. Your suggestion that a larger a/c unit would be needed is hogwash.

If you live in a two-story home, then heat from the first floor will definetely rise to the second floor... thus requiring additional cooling on the second floor (perhaps on a constant basis) would be needed to mimic the same environment as would be available on the first floor.

My suggestion is always build a single-story home; it is more efficient to keep cool in the warmer climates.

[IMHO]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

[bankruatsteve]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

So, if I have a 2-story home and run the A/C on the 2nd floor and the cool air comes down and bumps into the hot air coming up, then... aagh aagh. This is just so confusing.

[IMHO]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

So, if I have a 2-story home and run the A/C on the 2nd floor and the cool air comes down and bumps into the hot air coming up, then... aagh aagh. This is just so confusing.

LOL. It'll mix somewhere in there too - we're not talking about trying to dissolve oil in water - air mixes with air just fine

[fang37]

No need to be confused!

If in doubt, contact the A/C supplier.

BTW, per my previous post, a cool house is a combination of a number of factors.

We have a 2 storey home. Feeling - groud floor is cooler than the upper floor.

[Naam]

High ceilings do not cost more to cool with air-con

I'm sorry, but that's just not true.

Not only does more room volume cost more to cool, you also need a bigger AC to do the job.

OK sure, there's not much difference between 2.8 and 3.0M, but push it to 3.5M or more, and the spec for your AC just changed.

one can partly compensate for high ceilings and the higher volume by mounting the indoor units much lower. does not work of course with ceiling units.

in this context is worthwhile to mention that changing intake and blow-out is energy efficiency rubbish. old style unit sucked from down and blew out from top thus leaving the air volume above the unit rather undisturbed. the decision to change was made by economists to save production cost because a number of units are produced meant for cooling and heating.

the consumer pays for the technical nonsense if his unit is meant for cooling purpose only. his only consolation are the blatant lies concerning EER and SEER published by the manufacturers.

[Naam]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

Objection Your Honour!

during construction period of our home we rented for one year a double story penthouse with a huge opening to the lower (unused) floor. the three 12k btu/h units could hardly manage to get the living room down to 26ºC whereas the lower floor was 23-24ºC without any unit running.

[Psychic]

I agree, I have never been on the second floor of a house in Thailand where it was cooler than the bottom floor.

And, although I can not speak on the AC requirements, again the high ceilinged room is considerably cooler than the other rooms. The only reason I can suggest is that the hotter air rises and has more room to do so.

I would think, logically, that an AC unit that was positioned in the cooler part of the room would only activate at the temperature its set at. If the room temperature there was cooler then it wouldn't be running as much as in a lower ceilinged room which was consistently hotter.

[IMHO]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

Objection Your Honour!

during construction period of our home we rented for one year a double story penthouse with a huge opening to the lower (unused) floor. the three 12k btu/h units could hardly manage to get the living room down to 26ºC whereas the lower floor was 23-24ºC without any unit running.

I'm responding to a guy talking about a 10sqm box, saying there's no difference between a 2.5M vs 3.5M ceiling height

[technologybytes]

Forget the theory, I'll stick with my own experience. Higher ceilings are better and in my own experience cost no more to cool.

[Gumballl]

As mentioned earlier, cool air falls towards the ground, and hot air rises.

Not with AC turned on.... it all swirls around as the indoor unit blows out, and sucks in, air at the rate of 350 - 1,000 CFM

Objection Your Honour!

during construction period of our home we rented for one year a double story penthouse with a huge opening to the lower (unused) floor. the three 12k btu/h units could hardly manage to get the living room down to 26ºC whereas the lower floor was 23-24ºC without any unit running.

I'm responding to a guy talking about a 10sqm box, saying there's no difference between a 2.5M vs 3.5M ceiling height

What's your objection?

Sure the volume of the rooms are different, but in reality, for most average-sized people, they would only care about the air temperature from ground level up to 2m.

Who give's one thought of the air temperature above this level?

All things being equal, a higher ceiling is better. Take a Thermodynamics 300+ level course and you would know this.

[IMHO]

Good to see we still have the armchair experts active

A 10sqm room with a 2.5M high ceiling, with a typical, non-faulty, 9-10K BTU AC, with clean filters, is going to exchange the full air volume of the room in as little as about 3 minutes on the highest fan speed. Thermal buoyancy isn't a factor with this kind of air movement.

[Naam]

Good to see we still have the armchair experts active

A 10sqm room with a 2.5M high ceiling, with a typical, non-faulty, 9-10K BTU AC, with clean filters, is going to exchange the full air volume of the room in as little as about 3 minutes on the highest fan speed. Thermal buoyancy isn't a factor with this kind of air movement.

that is correct but the existence of 10m² rooms clashes with reality and, i admit, so does the extreme opposite of my home. below is a sketch showing grey shaded a total area of ~180m². room height is 3.60m, volume ~600m³, ACs are mounted at 2.20m. during the hot months the two units in the living room set @25ºC running full blast cooling the main living area to 26ºC whereas the unused areas (dining, library, foyer, tv-room) have a temperature of 28ºC. in the evenings these two units are shut down when i use my tv-room where the unit is switched on which provides 26ºC at a setting of 26º even though the room is open on two sides losing cool air.

[Anon999]

Yes, it’s that elusive “sweet spot” that I need to determine!!!

Just to clarify… the whole-house fan will feed into fully insulated ducting connected to a dedicated screened louvre at the gable-end of the Bali-style roof so that the expelled air will not enter the roof void, Other adjacent screened louvers will vent the roof void itself , as will the extensive soffit vents and all will be thermostatically fan assisted 24/7 to hopefully eliminate the possibility of condensation affecting the steel roof.

The house will be raised above ground level on either 1.4m or 2.4m high conc pillars (the "boss" didn't decide yet!) and will be on one level. The roof will be Off-white Colorbond with foil barrier on steel frames with suspended ceilings incorporating at least 150mm fiberglass insulation. The livingroom will have only one external wall -east facing with double or triple glazed French windows opening onto a balcony extending out just over 3m. The ceiling heights for other rooms which surround the livingroom to the south, west, and north (and will be used with aircon whenever they are used) will be 2,4m.

Your valued input is greatly appreciated. From other posts you have made on the forum relating to construction I can see you know what you are talking about.

When I built my 2 story house a few years ago I specified the ceiling height as 2.44 metres (8 feet) the length of wall boards. The aircon seems to cope very well, we have 7 of them and as the walls are autoclaved aerated concrete blocks the insides stay reasonable cool and dissipate heat quickly. There is also double glazing but that doesn't prevent heat build up in the room, something I learned in the UK from my extension.

Suggest you use lightweight galvanised steel for the roof, no need to worry about condensation then and also have a 'dry roof' construction. That permits the hot air to escape under the ridge tiles.