I've been informed that my damp problems are caused by condensation and
that a positive pressure ventilator would solve them. This seems to
consist of an extractor fan (with or without a heater) working in
reverse in the loft and feeding air to the landing. They seem to be a
very fancy price (£300 to £570 + installation).
Has anybody done this? Any recommendations?
It sounds like utter bollocks to me.
Condensation means either drag in cold air from outside, heat it and use
it to lower the RH, or simply heat the inside more to allow the air
itself to hold more moisture.
the firmer has ti be teh most expensive, especially with electric heating
heat recovery ventilation is much better
Or far cheaper, insulate the areas that are colder
(in-ep-toc’-ra-cy) – a system of government where the least capable to
These single fan magic solutions simply don't work. Whilst adequate
ventilation is a large part of the solution to condensation simply
putting a fan in the attic and blowing air in somewhere does not
guarantee any sort of air flow where it is needed. Additionally, most
houses are not sealed so leaking windows, holes where pipes come in
etc can create a pressure of their own which will reduce the fan
There are ventilation/extraction systems which do work but these have
input vents in every room and extract vents in kitchens and
That sounds like rubbish to me. You need to extract moist air at the
source of the moist air only. Other than that - insulation, especially
where moisture condenses.
Drawing air in and allowing it to distribute itself randomly will not
help at all, especially it will not help with your heating bills.
On Sunday, April 7, 2013 10:02:12 AM UTC+1, Another Dave wrote:
Bollocks, but not complete bollocks; there is a grain of sense in it that i
s being sexed up to make it attarctive to the ill-informed.
The recommendation was, undoubedly, made by someone offering to sell you a
positive pressure ventilation unit.
The real fix, as others said, is more ventilation (lower the indoor air Rh
, increases heating costs) and/or insulation (increase the surface temperat
ures above the air dew-point, lowers heating costs).
Extract fan(s) will make the space negative pressure with respect to outsi
de and the make-up air (cold and with entrained dirt) will be dragged in th
rough any gaps (open windows, cracks around doors, under floor boards, etc.
Positive pressure will have a supply air fan, ideally heated and filtered,
so air leaks out. It is used in clean rooms, but as ventilation systems co
sting vastly more than a simple fan. They have seized on the 'positive pres
sure ' buzz words to mis-sell their cheap tat.
There was a study done in 'Which?' (ISTR, decades ago, I've never seen it
mentioned since) in which ventilation systems were an effective cost-savin
g measure IF the costs of reduced cleaning were taken into account.
A trickle-ventilation extract fan with a humidistat sounds more like what
you'd need. Or a kitchen extract hood, if the moisture originates from coo
On Sunday, April 7, 2013 4:41:41 PM UTC+1, firstname.lastname@example.org wrote
He can give me the spare £400, so he doesn't feel like a cheapskate.
Actually the OP said the problem was damp, which he was told was caused by
condensation and the solution was the £500 positive pressure gizmo.
Did the salesman have a damp meter with green and red flashing LEDs?
The condensation suggestion may have just been the link to sell the gizmo
and is equally suspect.
I think I'd start by checking gutters, downpipes, roofs, flashings, air pa
ths into cold lofts, etc., the usual suspects re damp.
I'm the OP.
Alright, already. I've got the message.
For the past two weeks I've been running a couple of de-humidifiers I
borrowed from a neighbour (he's discovered two springs under his kitchen
and lives next to Well Cottage!). They do seem to work and I've just
this minute bought my own on e-bay.
I'll go with this for a while and see what happens.
I think there is more than one source of the problem. The kitchen floor
is tiles laid on top of the original quarry tiles (the house was built
in 1928) and there is almost certainly no membrane. In addition the log
stove chimney is not lined and I'm trying to get that seen to as some of
the damp shows signs of smoke. The other chimney is lined but has no air
bricks. The previous owners fitted double glazing (no trickle vents) and
cavity wall insulation (23 air bricks blocked up) etc, etc.
I'm expecting a long campaign :(
On Sunday, April 7, 2013 7:05:13 PM UTC+1, Another Dave wrote:
Damp is discussed on this forum, about old buildings;
Allegedly, an impervious floor covering (usually cement, but tiles could d
o) will reduce the evaporation from the floor, but shifts the problem up th
e walls. Similarly cement rendering will trap moisture within walls; they'r
e very keen on hacking cement off old properties, French drains and similar
stuff; search the archives.
If the neighbour has a spring, the water level must be high. Maybe you cou
ld investigate using some of it as grey water and thereby lowering the wate
The best way to fix condensation is at source with extract fans, run
when there is an activity going on.
Showers, bathrooms, cookers etc.
And/or, buy yourself a dehumidifier which has the fringe benefit that
it helps to warm the place up a bit.
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