The garage is unheated and damp, and I've noticed mildew on things.

I have left the doors and windows open for a couple of days and that
seems to have helped, but I'd like to do a bit better.

There's a chest freezer in there, that collects a lot of condensation on
the sides and lid.

I don't want to buy or run a dehumidifier unless absolutely necessary,
but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

Thanks,

Daniele

On 29/12/2015 15:58, D.M. Procida wrote:
The garage is unheated and damp, and I've noticed mildew on things.

I have left the doors and windows open for a couple of days and that
seems to have helped, but I'd like to do a bit better.

There's a chest freezer in there, that collects a lot of condensation on
the sides and lid.

I don't want to buy or run a dehumidifier unless absolutely necessary,
but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

Thanks,

Daniele


Car wax the outside of the freezer so it doesn't rust.
Collect the drips from it in a bucket and dispose of it outside.
You have a dehumidifier (just not a very good one).

There have been a lot of days in December where the outside air has been
saturated. You can't get rid of damp by ventilation alone when this is
the case. You need some heat from somewhere. A sunny window, the freezer
motor, a fan or a small heater/dehumidifier.

In message . com,
lid writes
On 29/12/2015 15:58, D.M. Procida wrote:
The garage is unheated and damp, and I've noticed mildew on things.

I have left the doors and windows open for a couple of days and that
seems to have helped, but I'd like to do a bit better.

There's a chest freezer in there, that collects a lot of condensation on
the sides and lid.

I don't want to buy or run a dehumidifier unless absolutely necessary,
but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

Thanks,

Daniele


Car wax the outside of the freezer so it doesn't rust.
Collect the drips from it in a bucket and dispose of it outside.
You have a dehumidifier (just not a very good one).

There have been a lot of days in December where the outside air has
been saturated. You can't get rid of damp by ventilation alone when
this is the case. You need some heat from somewhere. A sunny window,
the freezer motor, a fan or a small heater/dehumidifier.

I have been toying with the idea of using an air source heat pump to
control the air temperature, target 10deg.C, in an insulated garage to
allow use as a utility area. So far I have not progressed beyond a few
lazy brain cells:-)

--
Tim Lamb

On 29/12/15 17:25, dennis@home wrote:
There have been a lot of days in December where the outside air has been
saturated. You can't get rid of damp by ventilation alone when this is
the case. You need some heat from somewhere. A sunny window, the freezer
motor, a fan or a small heater/dehumidifier.

I run a dehumidifier in my shed for a couple of days every fortnight or
so in winter - pulls out about 14l of water and seems to keep the
condensation at bay (theres a lot of exposed wood so I aim to dry that
and let the buffer new damp).

In article ,
(D.M. Procida) writes:
The garage is unheated and damp, and I've noticed mildew on things.

I have left the doors and windows open for a couple of days and that
seems to have helped, but I'd like to do a bit better.

There's a chest freezer in there, that collects a lot of condensation on
the sides and lid.

If the freezer has an anti-condensation case heater, you should switch
it on. However, those often operate only around the door seal, and
that's to prevent condensation there freezing and sticking the seal
to the case.

I don't want to buy or run a dehumidifier unless absolutely necessary,

They don't work at outdoor winter temperatures anyway.

but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

That's a misunderstanding of the problem. The condensation forms on
the freezer where the cold is leaking out from the inside (at least,
that's the easiest way to think of it;-). The heat from the freezer
is actually very welcome, and the heated air will have a lower
relative humidity, not higher (unless the freezer is frost-free).

A friend has a large garden shed which they use for storage. Problem
was that many of the items in there would be damaged by damp, so I
designed a system in there to maintain the humidity at no more than
80%. This has been running for 15 months now, and it has worked
perfectly - there's been no damp in the shed over this period -
no new metalwork in there has gone rusty (which it used to before),
and there's no smell of damp timber or fabric. Whilst the outside
humidity often reaches 100%, the humidity in the shed has never
exceeded 81%.

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%. This has completely prevented any condensation forming over
the 15 month period. It has cost £55 in electricity over the 15
months (mostly in the winter), which is much less than the £200/month
they used to pay in storage rental space.

At some point when I have time, I will write up the system in a blog,
but basically, you need a low power heater (depending on thermal
properties of the garage) to kick in when relative humidity exceeds 80%.
One slight complication here is that most humidity sensors become wildly
inaccurate outside the 30-70%RH range. I use SHT75 sensors driven by
the Raspberry Pi directly, which are accurate from 0-100%RH.

If the air circulation and temperature uniformity are good inside
your garage, you might even get away with a 90%RH setpoint, but I
didn't have time to try that before the items arrived for storage.
(I did start with a 70%RH setpoint initially, and bumped it up.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Its science though is it not? Warm air holds more water vapour than cold
air, so one assumes the hot air around the exchanger in the freezer can mop
up the damp and then when it moves onto cold surfaces, it gives up its
water.
there is a reason why air conditioning units heat exchangers are normally
outside!

Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
"D.M. Procida" wrote in
message
...
The garage is unheated and damp, and I've noticed mildew on things.

I have left the doors and windows open for a couple of days and that
seems to have helped, but I'd like to do a bit better.

There's a chest freezer in there, that collects a lot of condensation on
the sides and lid.

I don't want to buy or run a dehumidifier unless absolutely necessary,
but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

Thanks,

Daniele

On Tue, 29 Dec 2015 23:00:38 -0000 (UTC), (Andrew
Gabriel) wrote:

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%. This has completely prevented any condensation forming over
the 15 month period. It has cost £55 in electricity over the 15
months (mostly in the winter), which is much less than the £200/month
they used to pay in storage rental space.

There's a number of systems that reduce humidity by monitoring the absolute
humidity inside and outside, and turn on a ventilator when it's drier outside
than in... Less useful in a shed than in a cellar, where the temperature can
differ greatly from the outside temperature.

Most of the systems are homebrew, Raspi, Arduino, or such; the commercial
systems tend to be expensive and limited.


Thomas Prufer

In article ,
Thomas Prufer writes:
On Tue, 29 Dec 2015 23:00:38 -0000 (UTC), (Andrew
Gabriel) wrote:

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%. This has completely prevented any condensation forming over
the 15 month period. It has cost £55 in electricity over the 15
months (mostly in the winter), which is much less than the £200/month
they used to pay in storage rental space.

There's a number of systems that reduce humidity by monitoring the absolute
humidity inside and outside, and turn on a ventilator when it's drier outside
than in... Less useful in a shed than in a cellar, where the temperature can
differ greatly from the outside temperature.

There are a few occasions when the absolute humidity (dew point) in
the shed is higher than outside. This tends to be in spring and autumn
around midday, and I have thought about adding a ventilator to kick in
when this happens. But it's not often enough to be worth rushing to do
it, so I haven't done it yet.

However, there are days on end when the RH outside is 100%, and even
periods when it's super-saturated (over 100% and moisture condensing
out on everything, dripping from trees, etc). Ventilation won't help
at all in these cases, and this is what you really need to protect the
shed contents from.

Most of the systems are homebrew, Raspi, Arduino, or such; the commercial
systems tend to be expensive and limited.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Wed, 30 Dec 2015 11:19:22 -0000 (UTC), (Andrew
Gabriel) wrote:

There are a few occasions when the absolute humidity (dew point) in
the shed is higher than outside. This tends to be in spring and autumn
around midday, and I have thought about adding a ventilator to kick in
when this happens. But it's not often enough to be worth rushing to do
it, so I haven't done it yet.

However, there are days on end when the RH outside is 100%, and even
periods when it's super-saturated (over 100% and moisture condensing
out on everything, dripping from trees, etc). Ventilation won't help
at all in these cases, and this is what you really need to protect the
shed contents from.

Yes -- much different if there are thick walls, buried. Apparently one can dry a
cellar well just with ventilation.

And I saw a website with a diy heat exchanger that ventilated and recouped the
heat from the exhaust. The heat exchanger was either very many soft drink
straws, or polycarbonate plates. And the heat exchanger tan into problems with
condensate freezing in sub-zero weather.

I have bag of (I think) zeolith, absorbs moisture and releases it again when
heated in an oven. It keeps the contents of one plastic box dry, if reasonably
well sealed. The bag absorbs about 200 grams of water.

Thomas Prufer

On 29/12/2015 23:00, Andrew Gabriel wrote:

A friend has a large garden shed which they use for storage. Problem
was that many of the items in there would be damaged by damp, so I
designed a system in there to maintain the humidity at no more than
80%. This has been running for 15 months now, and it has worked
perfectly - there's been no damp in the shed over this period -
no new metalwork in there has gone rusty (which it used to before),
and there's no smell of damp timber or fabric. Whilst the outside
humidity often reaches 100%, the humidity in the shed has never
exceeded 81%.

I read somewhere that you need to keep the RH below 60% to stop rust on
steel. Many new box girder bridges use dehumidifiers inside the boxes
rather than paint as its cheaper and lighter.

In article . com,
dennis@home writes:
On 29/12/2015 23:00, Andrew Gabriel wrote:

A friend has a large garden shed which they use for storage. Problem
was that many of the items in there would be damaged by damp, so I
designed a system in there to maintain the humidity at no more than
80%. This has been running for 15 months now, and it has worked
perfectly - there's been no damp in the shed over this period -
no new metalwork in there has gone rusty (which it used to before),
and there's no smell of damp timber or fabric. Whilst the outside
humidity often reaches 100%, the humidity in the shed has never
exceeded 81%.

I read somewhere that you need to keep the RH below 60% to stop rust on
steel. Many new box girder bridges use dehumidifiers inside the boxes
rather than paint as its cheaper and lighter.

At the start of this project, I didn't know what the value was,
or if it was simply that the atmosphere must be non-condensing
(i.e. less than 100% at metal surface). Also, I was suspecting
a different (lower humidity) requirement for timber and furnishings.

Based on what I've learned in doing this, I suspect the requirement
for steel is that the atmosphere must be non-condensing. I have not
measured the moisture content of the timber in there - I keep
forgetting to do this when I'm visiting. However, there is no
musty/damp smell which you often get in damp sheds/cellars/garages,
so I think the 80%RH limit seems to be working for the timber and
furnishings. What I don't know is if 90%RH would also work (it would
reduce the heating bill, but I can't experiment with the furnishings
which are now stored in there).

I have very accurate control on the humidity limit and the shed is
airy inside, with nothing stored up hard against the walls or floor.
If you don't have both of these, then the temperature (and consequently
the RH) will change in different places in the shed. Then it would be
necessary to lower the limit on the measured RH to try to ensure that
pockets where it is higher are still low enough to prevent dew point
condensation.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 29/12/2015 23:00, Andrew Gabriel wrote:

snip

I use SHT75 sensors driven by the Raspberry Pi directly, which are
accurate from 0-100%RH.

Wow, the SHT75 must cost more than the Raspberry Pi?

In article ,
Fredxxx writes:
On 29/12/2015 23:00, Andrew Gabriel wrote:

snip

I use SHT75 sensors driven by the Raspberry Pi directly, which are
accurate from 0-100%RH.

Wow, the SHT75 must cost more than the Raspberry Pi?

There are cheaper humidity sensors, but as I said, I needed some that
were accurate up to 100%RH. There is a cheaper version - SHT72, which
I think also works up to 100%RH but is not so accurate across the whole
range.

BTW, I think there's a Pi driver for these now, although there wasn't
when I did this so I had to write my own. They are similar to I2C, but
without any device addressing, so they need a dedicated bus for each one.
Timing is not critical (all I/O is clocked), so you can bit-bang it from
user-space, which is what I do. Connections can be made directly to the
Pi's GPIO pins without any interface buffers/logic, although you can't
drive more than a few feet of cable.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:

but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

That's a misunderstanding of the problem. The condensation forms on
the freezer where the cold is leaking out from the inside (at least,
that's the easiest way to think of it;-). The heat from the freezer
is actually very welcome, and the heated air will have a lower
relative humidity, not higher (unless the freezer is frost-free).

Warmer air can hold more moisture than colder air. Passing it over the
condensed moisture on the surface of the freezer, and then out of the
garage, would seem like a neat trick if it could be achieved.

I don't mind if that makes the garage colder... unfortunately, the thing
that mostly warms it up is people running around playing ping-pong in
it, which visibly contributes to the humidity.

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%.

I'd definitely be interested in giving that a go if you can provide mor
information. I have a Pi Zero begging to be used for something like
that.

Daniele

In article ,
(D.M. Procida) writes:
Andrew Gabriel wrote:

but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

That's a misunderstanding of the problem. The condensation forms on
the freezer where the cold is leaking out from the inside (at least,
that's the easiest way to think of it;-). The heat from the freezer
is actually very welcome, and the heated air will have a lower
relative humidity, not higher (unless the freezer is frost-free).

Warmer air can hold more moisture than colder air. Passing it over the

Yes, so heating the air with a fixed absolute humidity results in
a reduction of relative humidity.

condensed moisture on the surface of the freezer, and then out of the
garage, would seem like a neat trick if it could be achieved.

The moisture on the surface is condensing out because the freezer
case is colder than the air, and below the dew point. If you collected
the condensate and piped it out of the garage, that's actually a mini
dehumidifier. Although parts of the freezer case are colder than the
air, the freezer outputs more heat into the garage than the cold parts
of it remove. Its net heat output to the garage is its power consumption
plus the latent heat of condensation that forms on it and is removed
from the garage in liquid form without evaporating.

The heat from the freezer is a bonus because it will be raising the
temperature of the garage (slightly), and when air comes in from outside,
its relative humidy will be reduced when it's heated. If the air and
garage were uniformly heated, it would make condensation in the garage
impossible. Unfortunately, the heat output from the freezer is unlikely
to be enough and the temperature rise won't be uniform.

I don't mind if that makes the garage colder... unfortunately, the thing
that mostly warms it up is people running around playing ping-pong in
it, which visibly contributes to the humidity.

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%.

I'd definitely be interested in giving that a go if you can provide mor
information. I have a Pi Zero begging to be used for something like
that.

Unfortunately, it's a piece of software I wrote 17 years ago and have
hacked about ever since, and it's not in any state to be opensourced.
Maybe when I retire, I'll rewrite it designed for Raspberry Pi, rather
than as the current set of emulators of other products I used to use
years ago (and still do in a couple of installations which well predate
the Pi). I am surprised something like this isn't readily available
already.

However, for just this application, a shell script loop reading the
humidity and deciding to switch a heater on or off is all that's
required (providing there is now a Pi driver for a suitable humidity
sensor).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 30/12/2015 20:28, D.M. Procida wrote:
Andrew Gabriel wrote:

but perhaps the warmer (therefore damper) air around the freezer could
be ducted outside with the help of an extractor fan - it seems a shame
to waste the heating and damp-collecting properties of the freezer.

That's a misunderstanding of the problem. The condensation forms on
the freezer where the cold is leaking out from the inside (at least,
that's the easiest way to think of it;-). The heat from the freezer
is actually very welcome, and the heated air will have a lower
relative humidity, not higher (unless the freezer is frost-free).

Warmer air can hold more moisture than colder air. Passing it over the
condensed moisture on the surface of the freezer, and then out of the
garage, would seem like a neat trick if it could be achieved.

I don't mind if that makes the garage colder... unfortunately, the thing
that mostly warms it up is people running around playing ping-pong in
it, which visibly contributes to the humidity.

The system uses a Raspberry Pi to continually monitor the humidity,
temperature and dewpoint inside the shed (and also outdoors for
comparison). It switches on a heater in the shed if the RH exceeds
80%.

I'd definitely be interested in giving that a go if you can provide mor
information. I have a Pi Zero begging to be used for something like
that.

Daniele


I think I might insulate, if only for the comfort of the ping pong players

In message , Thomas Prufer
writes
On Wed, 30 Dec 2015 11:19:22 -0000 (UTC), (Andrew
Gabriel) wrote:

There are a few occasions when the absolute humidity (dew point) in
the shed is higher than outside. This tends to be in spring and autumn
around midday, and I have thought about adding a ventilator to kick in
when this happens. But it's not often enough to be worth rushing to do
it, so I haven't done it yet.

However, there are days on end when the RH outside is 100%, and even
periods when it's super-saturated (over 100% and moisture condensing
out on everything, dripping from trees, etc). Ventilation won't help
at all in these cases, and this is what you really need to protect the
shed contents from.

Yes -- much different if there are thick walls, buried. Apparently one
can dry a
cellar well just with ventilation.

And I saw a website with a diy heat exchanger that ventilated and recouped the
heat from the exhaust. The heat exchanger was either very many soft drink
straws, or polycarbonate plates. And the heat exchanger tan into problems with
condensate freezing in sub-zero weather.

I have bag of (I think) zeolith, absorbs moisture and releases it again when
heated in an oven. It keeps the contents of one plastic box dry, if reasonably
well sealed. The bag absorbs about 200 grams of water.


Zeolite, it's what they use in desiccant dehumdifiers
--
Chris French

On 29/12/2015 23:00, Andrew Gabriel wrote:
In ,
(D.M. Procida) writes:

I don't want to buy or run a dehumidifier unless absolutely necessary,
They don't work at outdoor winter temperatures anyway.


ICBW but I thought dessicant wheel types would.

Andy

In article ,
Vir Campestris writes:
On 29/12/2015 23:00, Andrew Gabriel wrote:
In ,
(D.M. Procida) writes:

I don't want to buy or run a dehumidifier unless absolutely necessary,
They don't work at outdoor winter temperatures anyway.


ICBW but I thought dessicant wheel types would.

You might be right.
However, these use more power (for the same level of dehumidifying),
and I suspect a heater of the same power rating would be just as
effective.

The heater I use in the shed is a 1kW oil-filled radiator, but with
a series diode to limit it to 500W. When the system is running, the
heating duty-cycle is so low that when you feel the radiator, you
would not even think it has been on. The power output required to
drop the RH from 100% to 80% at low temperatures simply by raising
the temperature is remarkably low.

I had not expected this initially and using a heater was going to be
a stop-gap before trying a dehumidifier, but when I found how little
heat was required, I dismissed using a dehumidifer in the shed.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Hi Andrew

On Friday, January 1, 2016 at 10:01:34 PM UTC, Andrew Gabriel wrote:
In article ,
Vir Campestris writes:
On 29/12/2015 23:00, Andrew Gabriel wrote:
In ,
(D.M. Procida) writes:

I don't want to buy or run a dehumidifier unless absolutely necessary,
They don't work at outdoor winter temperatures anyway.


ICBW but I thought dessicant wheel types would.

You might be right.
However, these use more power (for the same level of dehumidifying),
and I suspect a heater of the same power rating would be just as
effective.

The heater I use in the shed is a 1kW oil-filled radiator, but with
a series diode to limit it to 500W. When the system is running, the
heating duty-cycle is so low that when you feel the radiator, you
would not even think it has been on. The power output required to
drop the RH from 100% to 80% at low temperatures simply by raising
the temperature is remarkably low.

I had not expected this initially and using a heater was going to be
a stop-gap before trying a dehumidifier, but when I found how little
heat was required, I dismissed using a dehumidifer in the shed.


Does that work across the whole shed with a single heater? I would have expected
the heat would not reach all necessary areas sufficiently.

I have a 1.5 width garage I would like to do something similar with, and was
wondering about a dehumidifier.,,

Thanks
Jon N

On 01/01/2016 21:58, Andrew Gabriel wrote:
In article ,
Vir Campestris writes:
On 29/12/2015 23:00, Andrew Gabriel wrote:
In ,
(D.M. Procida) writes:

I don't want to buy or run a dehumidifier unless absolutely necessary,
They don't work at outdoor winter temperatures anyway.


ICBW but I thought dessicant wheel types would.

You might be right.
However, these use more power (for the same level of dehumidifying),
and I suspect a heater of the same power rating would be just as
effective.

The heater I use in the shed is a 1kW oil-filled radiator, but with
a series diode to limit it to 500W. When the system is running, the
heating duty-cycle is so low that when you feel the radiator, you
would not even think it has been on. The power output required to
drop the RH from 100% to 80% at low temperatures simply by raising
the temperature is remarkably low.

I had not expected this initially and using a heater was going to be
a stop-gap before trying a dehumidifier, but when I found how little
heat was required, I dismissed using a dehumidifer in the shed.


A desiccant dehumidifier would use about 400w for a smallish one while
actually running.
This would heat the shed at least as much as your 500w heater as it
would recover the latent heat from the water it condensed while the air
is damp.

In article ,
jkn writes:
Hi Andrew

On Friday, January 1, 2016 at 10:01:34 PM UTC, Andrew Gabriel wrote:
In article ,
Vir Campestris writes:
ICBW but I thought dessicant wheel types would.

You might be right.
However, these use more power (for the same level of dehumidifying),
and I suspect a heater of the same power rating would be just as
effective.

The heater I use in the shed is a 1kW oil-filled radiator, but with
a series diode to limit it to 500W. When the system is running, the
heating duty-cycle is so low that when you feel the radiator, you
would not even think it has been on. The power output required to
drop the RH from 100% to 80% at low temperatures simply by raising
the temperature is remarkably low.

I had not expected this initially and using a heater was going to be
a stop-gap before trying a dehumidifier, but when I found how little
heat was required, I dismissed using a dehumidifer in the shed.

Does that work across the whole shed with a single heater? I would have expected
the heat would not reach all necessary areas sufficiently.

The heater is in the middle of the shed. The owner got some cheap
Celotex/Kingspan and insulated the roof initially, and later some
of the walls, but never finished it.

Everything in the shed is raised on old pallets and spaced slightly
away from the walls, so there's air circulation to get the heat circulated.
It seems to work. The temperature/humidity sensing is near one of the
walls, which should be one of the worse positions in terms of higher
relative humidity and lower temperature.

I have a 1.5 width garage I would like to do something similar with, and was
wondering about a dehumidifier.,,

I already had the ancient oil-filled radiator. (It had been my
grandmother's, but being old, it's very well made and I rewired it
some years ago.) If it had been necessary to buy something, given
what I now know, I would have recommended a couple of tubular heaters
to place at each end, for better heat distribution. CPC has them on
offer occasionally. I would avoid a heater with any particularly hot
parts such as a radiant heater or bare wire heated convector heater.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 02/01/2016 17:28, dennis@home wrote:

A desiccant dehumidifier would use about 400w for a smallish one while
actually running.
This would heat the shed at least as much as your 500w heater as it
would recover the latent heat from the water it condensed while the air
is damp.

There's the capital cost to consider too. Though it does look as if
they're not much over £100.

Andy

On Friday, 1 January 2016 22:01:34 UTC, Andrew Gabriel wrote:
In article ,
Vir Campestris writes:

I don't want to buy or run a dehumidifier unless absolutely necessary,
They don't work at outdoor winter temperatures anyway.


ICBW but I thought dessicant wheel types would.

You might be right.
However, these use more power (for the same level of dehumidifying),
and I suspect a heater of the same power rating would be just as
effective.

Far from. When we put a desiccant type dehumidifier into an unheated building it filled its tank daily.


NT