Heat & cooling requirements are dependent more on surface area than
volume. If you increase the height of the walls, let's say in a
rectangular prism, volume increases directly with wall height. But total
surface area, including the area of the top and bottom, doesnt increase
as rapidly. A cube doubled in height has twice the volume but only one
and two-thirds times the surface area. A rectangular prism 50x50x8
increased to 50x50x10 has 1.25 the volume at 1.06 times the surface
But temperature gradient is also an issue. Heat rises so the extra foot
at the top will contain the hottest air which means that the average
room temperature must be higher to get the same temps down low where the
people are as they don't get a foot taller with the higher ceiling.
I'll bet that the extra 6% of surface area combined with that new
surface area having the highest temperature delta with the outside will
raise heating costs closer to 10%, or roughly the same amount as the
increase in wall height.
This can be mitigated with ceiling fans or with radiant floor heat, but
it is still a factor with higher ceilings.
It all depends on where the theromstat is. If the theromstat is at 5',
higher ceilings may even be somewhat beneficial as the hot air is
higher up than it would be in lower ceilings. Of course, the cool air
has longer ways down, exposing it to 'more' hot air at the top, but
there's nothing saying the air would be any more hotter at 8' or 10'
assuming the walls have the same insulation value.
subdivision homes and additions, 8' or 10' ceilings don't have much of
an impact on HVAC capacity, if any. For homes HVAC capacity is
typically determined on a sf basis, rather than a volumetric basis. Not
surprisingly, key factors in the energy calcs are whether the HVAC is
in a conditioned space, garage or attic, where the return air grille
is, what's the insulation of ducts, the tint value of the windows, the
SEER value of the unit and of course # of windows and house
orientation. These have far greater impact, or are assumed to have
greater impact, in the codes and calc programs.
Re: cooling, tho', it's always been my impression that, in hot climates,
part of the purpose of a higher ceiling was/is to draw heat upwards from
the living area - conversely, lower ceiling heights in Northern houses
helped keep heat down near the living area. So, for heating, it'd cost
less to heat rooms with lower ceilings (tho' I've no idea how much less).
It's also a matter of comfort. I've found the higher ceiling height of
this house (Houston) more comfortable in the warm weather, whereas the
lower ceilings of the (former) Massachusetts house were less comfortable
during warm days. Although I also realize that might be more mind than
matter, due to the relative "open/breezy" feel of a heigher ceiling versus
the "protective" feel of a lower one.
But that's merely my impression - I don't know the thermodynamic reality.
Well it might be because people are getting taller
on average. (I'm 6'+ ,wife is 5'8", which is only
slightly above average). We find we need to raise
the fridge, dish-washer, counters and practically
everything to be comfortable otherwise we're always
stooping. We're building a cabin with 9' ceilings
because as Mr. Peruna put's it, "it feels better".
We went up 10' and then dropped a suspended
ceiling to 9' to accomodate 1' of insulation. That
was fairly easy to construct, using 4' wide panels.
The panels are placed at 8' then the insulation was
applied and then the panels were lifted and slid
along guides (2x2's at 9'). The panels are pricey
$25 per 4'x8' x 1/8" but the're tough and durable,
and certainly provide an excellent vapor barrier.
That's right! Hell I have to sit down to pee, because
the damn thing is so far away and it splashs if I stand
to pee. Really that's a very good point!
I had a plumber visit today asking for specs and now
I'm going to study raising the W/C in any case, hey
that's great...thanks need to think.
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