The weather on the Pacific Coast from Northern California to British
Columbia tends to be warm and dryish in the summer but cool and damp
in the winter. Depending upon where you are, there may be no need
for summer air conditioning / cooling. So while for much of the
continent, the season for dehumidifying is the summer, on the left
coast it is the winter.
Dehumidifiers produce heat, therefore their energy efficiency is
important in continental applications. However, on the left coast,
they are used mostly in the winter, so the heat they produce is
mostly a slightly more expensive form of something you're going to
do anyway: heat the air in the house.
On the other hand, we may allow our rooms to cool below 65 degrees.
I know that I do. But as I discovered yesterday when reading the
manual of a Classic ECD15E Dehumidifier purchased from Home Hardware,
operation of a dehumidifier at below 65 degrees is frowned upon, for
two reasons: efficiency goes in the sink (so to speak), and the
coils can freeze up, causing waste and damage. So much for the idea
of moving the unit from room to room, leaving it in an unoccupied
room. We could have lived with leaving it in the living room and
allowing the dry air to seep into less used corners of the house, but
the fan of the unit is too loud. Unfortunately, loud fans seem to be
a fact of life in Canadian appliances (gas fireplaces, fume hoods...).
So I took the unit back, and Home Hardware kindly refunded the
purchase price of $cdn190 plus taxes, which I thought rather a lot
considering its simplicity.
For west coast uses, energy efficiency isn't so important, but the
ability to operate (or at least the ability not to break down) at 65
degrees or less IS important. Those are two big differences from the
dehumidifiers used in "continental" climates.
Any suggestions? Canadian Tire has a line of six dehumidifiers, all
made by "Simplicity" (= Danby). I went out to Canadian Tire here,
and found that they did have a couple of these in stock, but they
were all in crates, no display. And no Efficiency Ratings for any of
them. That was at the beginning of the search, so perhaps I was
picky. Since then I've checked Future Shop (none), London Drugs (
none), Home Hardware (just the one mentioned, and a larger model of
the same), Zellers, Superstore (their online catalogues don't list
lists no less than 15 units, but after looking at a couple, I see no
sign of low temperature operation, no mention of noise levels.
Going outside Canada, I saw a DeLonghi dehumidifier advertised as
offering operation down to 44 F. Not sure how I'd get one here.
So, does anybody manufacture a "Left Coast Friendly" dehumidifier,
and how can I get one in Canada? Our house is only 900 square feet,
so the smallest size will probably be appropriate.
Finally, wouldn't a dehumidifier be more efficient if it took the
warm moist air in at ceiling level, then expelled warm dry air at
floor level? That would recirculate the air for those of us with 8-
foot ceilings and thus no ceiling fans. Yet consumer dehumidifiers
are universally designed to sit on the floor. I'm not sure what I'm
suggesting, maybe a permanent installation in one room, or maybe
something that can be moved around like a pole lamp.
Maybe not. NREL says Seattle has these average temps and humidity ratios:
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
40.1 43.5 45.6 49.2 55.1 60.9 65.2 65.5 60.6 52.8 45.3 50.5 F
..0042 .0045 .0046 .0051 .0061 .0072 .0082 .0085 .0078 .0065 .0051 .0044
The humidity ratio w is the number of pounds of water vapor per pound
of dry air. It does not depend on the air temperature, and it doesn't
change much in 24 hours. The relative humidity is the number of pounds
of water vapor per pound of air divided by the maximum number of pounds
of water vapor the air can hold (at 100% RH) at a certain temperature.
That could be true in a Canadian airtight house with humidity sources,
unlike air-leaky US houses with energy-wasting winter humidifiers...
It's cheaper than electric resistance heat, with a COP of about 1.6.
You can measure this with a Kill-a-Watt meter and a measuring cup.
Turn on a small exhaust fan with a humidistat when the indoor RH rises to
60%. In January, w = 0.0042 makes Pa = 29.921/(1+0.62198/w) = 0.201 "Hg.
Indoor air at 60% RH and absolute temp T (R) has Pi = 0.6e^(17.863-9621/T),
approximately, and Pa = Pi makes T = 507.5 R or 507.5-460 = 47.5 F, so
you can dehumidify the house with an exhaust fan as long as the indoor
temp is at least 47.5 F. If you want to save more energy, take advantage
of weather fluctuations and hygroscopic house materials and do this less
often, only when the outdoor air is warmer and drier than average (during
the day) in wintertime and cooler and drier (at night) in summertime.
Maybe not. Diffusion and convection make the water vapor pressure and the
humidity ratio of the air near the ceiling and floor about the same, even
though humid air rises.
Thanks for your comments, Nick!
I'm not sure how the absolute figures given above relate to the
experience that everyone who lives here has. Wouldn't RH be more
pertinent? I also doubt the accuracy of the figures. Ave. Temp. of
50.5 F in December? Nonsense, or a typo. Our own experience here, and
I don't think Seattle is too much different (although Seattle is
definitely wetter) is that it does not rain in August, and if it does
rain, the ground can be "bone dry" again in half an hour. In November,
on the other hand, it seems to rain constantly; your lawn will be a
quagmire. Water tables rise, and the moisture evaporates through your
basement walls into your living space.
I'd suggest that the moisture figures above reflect a) the fact that
warmer air is able to carry more water vapour and perhaps b) some sort
of filtering out of the effect of rain.
Airtight houses in Canada tend to be where the climate is severe. The
ideal place is Saskatchewan, which has hot summers and severe winters
with lots of sunny days. Airtight, passive solar, summer-shading
overhangs ... all work out well in Saskatchewan. There they have a
"continental climate" which would not likely need dehumidification in
Here in coastal British Columbia, construction tends to be more leaky.
And the case in consideration, our house, is a leaky house built in the
1930s. This thread is the result of an Energuide energy audit, which
resulted in the consultant telling us that we should make the house
more airtight, but that BEFORE we did that, we had to deal with the
That's reassuring. We're also looking forward to the subjective
feeling of warmth in dry air at a temperature where we would feel cold
in damp air.
Summertime is never an issue here. I'm afraid that the most
hygroscopic house materials are the books. Don't want to store
moisture in our books. So it looks like you also prefer exhaust fans
to dehumidifiers. My concern is that the warm damp air gets replaced
by cold damp air from the basement or outside. I'd really like to give
dehumidification a chance before making another hole in the wall.
By "humidity ratio", do you mean "relative humidity"? So, let's say
that the air at 70F and 70% humidity at ceiling level, but 65F and 70%
humidity at floor level. Something like that? Then I submit that this
could still be an advantage because of the dehumidifier's greater
efficiency at 70F than at 65F.
Oops. A typo. Shoulda been 40.5, with 35.8 and 45.1 average daily min and max.
I rechecked the rest of the numbers, which look OK.
Maybe that's where your water vapor is coming from. A 1930s house with
no vapor barrier under the basement floor?
Dunno about rain. Warmer air can carry more water vapour.
Airtight houses need dehumidification in wintertime because they contain
humidity sources, people breathing and showering and washing floors and
cooking and so on, as well as damp basements. A perfectly airtight house
would let the indoor RH rise until condensation happens on the indoor
surface of windows.
Sounds like you have a major indoor humidity source.
That's backwards :-)
Also concrete, wood, paper, fabric, and so on.
The RH might range from 30 to 60% with no damage.
Cold air tends to be drier than warm air. You have my numbers, which you
seem to have ignored. It isn't hard to make a hole in a window. You may
already have an exhaust fan in a kitchen or bathroom.
No. I already explained the difference. You seem to have ignored that too :-)
The water vapour could be coming from the basement, yes, it is likely.
There is no stairway for the moisture to come up to the main floor,
just the furnace and a few small holes for plumbing. Yet rise it does.
Is it? In places like Saskatchewan, they make a joke about the temp
being minus 40 but tolerable because "it's a dry cold". You can be
sure that when those same people retire to British Columbia, they often
feel (subjectively) colder even though the temperatures are oh 40 C
warmer, because of the dampness of the cold. And the most harrowing
tales of winter misery are not from the Yukon, but from houses in damp
Books are made of paper. If the moisture condenses, it can easily
evaporate from wood or fabric, but not so easily from books in
bookcases against a wall.
That shows that the RH is frequently above 60% because the books in my
office, next to the wall, do get a touch damp.
I questioned their applicability. I remember about 25 years ago I
wanted to get an old house in Ottawa insulated. The main choices at
the time were blown in cellulose and urea formaldehyde. I was dubious
about the UF, so I asked the contractor to provide "proof" that it was
OK. Surprisingly, they provided lab studies which "proved" that UF was
OK. I looked at the figures and the methodology, and concluded that in
the real world there was no way that UF foam could be blown the way it
was in the lab, so I went with cellulose. A couple of months later,
the issue blew up and I luckily didn't have to take the contractor to
court or demolish the house etc.
So I'm not sure what your numbers mean in this context. It can rain
zero days in August, and 29 days in November, yet August is
considerably damper than November. I can only think that those figures
somehow have the rain column shunted off into another category. Also,
the temperature inside the house does vary. In summer, we allow the
temp inside the house to go up to 76 or even 80. It is still
comfortable; if not, we can go outside under the grape arbour. At
other times we might let the temperature fall to 65 or even 62 and put
on a sweater. Those are the times when the vapour might condense out,
and those are the times we might need the dehumidifier.
I hadn't thought of that.
Ooops, sorry, I have a selective memory. Sometimes it doesn't cotton
on to terminology. Maybe I'll remember now.
But this is interesting ... the air at the top of the column might be
70F, with an RH of 50%, but at the bottom of the column 65F with the
same "humidity ratio" and therefore a higher RH. The warmer air might
not activate the unit's humidistat. That is consistent with the
observation that in the morning when we wake up, most of the
condensation is at the bottom of the window; the top may be clear. It
might also explain how the basement is a source of humidity to the main
part of the house: warm damp air rises through cracks, but never has a
chance to settle back down into the basement. And finally, it makes me
think that this old house might be more air-tight than I thought it
was. The wall construction is peculiar, as it includes 1" thick
horizontal planking. Maybe that traps a bit more of the moisture which
would otherwise escape.
More dehumidifier investigation: Local stores (to Nanaimo, BC):
Zellers and The Bay don't sell them. Wal*Mart has a Fedders unit whose
model number (D4989M) does not match any specs on the Internet. The
closest source for Bionaire in Canada is a dealer in London, Ontario
(over 2,000 miles away). No local refrigeration outlet has a
dehumidifier in stock, though one said he could order a Friederichs D30
unit for $cdn488. As reported earlier, there seem to be at least
three manufacturers (Bionaire, Soleus, Surround) who produce a small
dehumidifier with a noise level around 40 dBA and some sort of
anti-frost protection so that the unit can be allowed to operate at
temps of 65 or lower. The latter two seem not to be available in
The COP doesn't matter as far as adding heat to the house goes. A kwh of
electric to run a dehumidifier adds a kwh of heat to the building, just like
a kwh of electricity through a resistance heater.
The only difference is a kwh of electric through a dehumidifier not only
adds a kwh of heat to the building, it removes some amount of moisture from
Care to explain where the extra 0.6 kwh came from??
Granted the vaporization energy removed from the moisture gets dumped into
the room as latent heat, but that energy was always there, you've just used
some entropy from the electricity to change the heat of vaporization to
One kwh of energy into a dehumidifier means one kwh of energy added to the
house. Period. No miracle COP will add more energy to the house.
I see daestrom's point from a Physics point of view, but in
practicality I agree with Nick. With months of heating season ahead,
you have damp air in your house. What can happen to that air? It can
be ventilated, exhausted from the house (and, in most climates,
replaced by drier air) and the vapour energy is simply lost (to the
homeowner). The only way to keep the energy is to condense the vapour
inside the house, and the best place for the condensed vapour is down
the drain (or in houseplants), thanks to a dehumidifier. Not in your
books or insulation or constantly on your windowpanes.
The only problem with that here in NY is, we don't have a lot of 'damp air'
in the house in the winter time. Quite the opposite, because of low outside
temperatures, the house can be quite dry and we have to run a *humidifier*,
not a *dehumidifier*. Not for any sort of energy, but just for
The only time we need to run a *dehumidifier* is in the basement area in the
summer time. These units cool the air to remove moisture, then re-heat the
air from the condenser section of the vapor-cycle. Net result is it warms
up the basement slightly.
But I guess I can see where in some climates, where the winter temperatures
don't get too low, the dampness can be a bother. But seems like if it gets
down to say 40F outside , then when you warm your home air up to 70F you've
got just the right humidity, not too damp at all.
See subject line, "Pacific Coastal Dehumidifier". Here in Canada, it
seems difficult to get a dehumidifier you could put in your living
space (all the ones I have seen are too loud, they might go in the
basement) because so much of Canada has a Continental climate not too
dissimilar from New York.
Some houses, such as my own, have humidity excess from late September
until June. Aside from the Pacific Coastal climate, those in other
areas could have the same challenge if their house is built tightly, as
Nick pointed out.
Not an air leaky house but just a large heated air differential. Many add heat
exchangers to increase the "leaky house"
Going from -30C to +21C via heating leaves very little moisture (rh) despite the
sweating and cooking people.
wrote in message
Only for as long as it takes the water to evaporate again.
UNLESS you're clever enough to dump the condensate outside
the building envelope. At that point, whether you gain any
extra depends on whether it takes more energy to heat up
the condensate again, or to heat up the air-volume that you
have to acquire to replace it.
Yes, you're right I meant raising the sensible heat.
But if the basement or whereever has 100% RH at 50F, then your dehumidifier
is discharging it's heat at about 55F, not much use there. I have never
seen a dehumidifier that can extract moisture in a 50F basement and direct
the heat into a 70F house.
The only dehumidifiers I've seen take the air and cool it to remove
moisture, then warm the same air back again with the condenser coil of the
same vapor cycle. Sure, in 68F basement with 80% RH, you can warm the air
out of the dehumidifier to a higher temperature, but it's still in the
basement. In winter, when the basement is 50F, your dehumidifier will only
succeed in warming the basement air to 55F or so. Still not much use in
You have a dehumidifier with separate evaporator and condenser coils so you
can place one in the basement and one in the living space? And able to work
well with a 30 F delta temperature? Not your 'average' dehumidifier.
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