Removing damp from basement

[t8769]

A friend has made a bedroom in a small cellar which has limited ventallation, and its started to get damp. She's often away and wants to leave something down there to ventallate it.

Its difficult to put a dehumidifier down there as there's no where for hte draining pipe to go and they don't want to keep carrying water out.

If she puts a ventallation fan in, it'll cost a lot in heating as hot air is blown out of the house.

Is there any way she can get air into there, either with a pipe that blows or sucks air, or some other contraption that removes humidity but will take the water out.

The cellar is only accepsable by stairs, but does have a ventallation grill.

thanks

[Fash]

One option is to use a "heat recovery ventilator". This is basically an extraction fan with a heat exchanger which warms the incoming air so reducing the heat loss. If you google it you'll get lots of options of various sizes and controls. You can for example get them with a humidistat control to only turn on when it get's too damp.

I could put some links, but once you know what to look for it's pretty straightforward to find something. You do need a slightly bigger hole than for a standard ventilation fan but not much.

Fash

[meow2222]

Dehumidifier works out cheaper all said. You can add a condensate pump if you want to route the water up a floor. Carrying a gallon of water out once or twice a week is no big deal really.

Its also poss to use a fan to exchange air betwen celler and ground floor, and put your dehunid on the ground floor, but this is less effective and allows little possibility of differing heating.

NT

[Stuart Noble]

With ventilation I'd say a DH is a complete waste of time. You will simply be sucking air in from the world at large. Reassuring when you see how much water it generates, but ultimately pointless. A sealed space is a different matter.

[meow2222]

Venting to the rest of the house merely moves the damp from one location to another, where it is extracted. There is no reason to seal a room up to dehumid it.

NT

[mail]

On 28 Sep, 08:30, t8769 wrote:

Dear T 8769 Your friend was ill-advised to do this without considering all the necessary factors in the first place and if it is a legally habitable room (a bedroom) it must, surely, have a window? Absent a window I may be wrong but I think it will not conform to Building Regs and she puts herself at risk should she put any guests or any other person than herslef in such a location should they come to harm. That said I think she needs to determine if the dampmess is as a result of failure of the tanking or condensation now that it is tanked. If the former then my advice is to start again or just use it for storage. If the latter then all the normal condensation controls can be applied eg insulate the walls internally to keep the dew point up, control the water vapour entering, (a bit difficult if someone is sleeping!) and providing ventilation. How to do the ventilation all depends on the layout but in most houses with cellars there are suspended timber floors (ok not all!) and if there are suspended floors there are two routes (at least) to ventilate to the exterior, I would introduce one at the front and one at the back (or sides - whatever) such as to establish a flow thru from the outside just as one would with a window. I would have the vents controllable with, say, trickle vent capacity and this together with heating should make the place less prone to condensation particularly if someone is sleeping in it. A dehumididifer would be a complete waste of time unless you were able to seal the area from other wet air and would not be appropriate for anything other than a one-off drying operation say after a flood. (ok you could put one in on a humidistat but that is curing the symptom not the problem). Chris

[meow2222]

Sounds like you've not done it. Its very effective.

NT

[Steve]

How can a dehumidifier be effective in this situation?

Stuart and Chris have made the point that a dehumidifier would need to be in a sealed room to be effective and this is fact.

Unless you have a way of knowing where the individual water molecules in your house originated from and have a way of identifying said molecules and, then somehow, cleverly diverting those nasty extra water molecules elsewhere so that they went nowhere near your dehumidifier?

Dehumidifiers have their place but as Chris has said you must realise that they are not a cure and that their use will only help drying out and then only if they are used correctly.

Steve

[meow2222]

I'm sorry but its not, and I know that from years of using them.

huh?

It depends. In some cases theyre all the treatment thats needed, and in some not so. For cellars theyre cheaper and more energy efficient than unnecessary ventilation, and often all that's required to make a place healthy.

All habitable rooms should have some ventilation, so if the cellar has none it will need it, but if its still damp, a dh is a simple solution.

You can use them for one off events such as flooding, or for ongoing control of excess damp, or for other purposes such as drying clothes etc.

NT

[mail]

Dear NT Years of use, per se, do not change the laws of physics. Think about the process and you will see that your experience is telling you something that is not what you have deduced it is. Here we have a cellar - which is wet either from condensation or failure of tanking. For the purposes of our discussion it matters not which. The cellar has access to the rest of the house ( a door) and some minimal ventilation (see the original post). Water molecules travel in air at a considerable speed and consider the findings of Dalton with respect to vapour pressure. Install a dehumidifier in a room which has open windows or ANY access to open air and you are not dehumidifying that room but the rest of the world. Not surprising that it fills up the machine with lots of water. As part of my professional work I have been responsible for designing dehumidification for flooded (be it post Fire Brigade, loft tank failure, roof failure, storm damage or whatever) buildings from Grade

1 listed properties of national importance to 3 up 2 down terraces in Balham. The proceedure is to install the deumidifier in the area concerned and close all windows and doors supplementing if necessary with duct tape or polythene (if leaky as many old buildings are) introducing (if in winter) electrical for remote source heat (dry heat without use paraffin burners etc) humidistats, RH measurment apparatus and most importantly to record the volume of water and produce a graph v time to measure progress. Absent a significant reduction in the source of water VAPOUR from sources external to the cellar all you are doing is collecting water from the environment as well as some from the cellar and not putting the drying force where it is required - the walls of the cellar. Hope this evidential approach to the discussion results in acceptance or an evidential-based counter argument... Chris

[meow2222]

Evidence based... with normal ventilation if I ran the dh the room stayed dry, if I didnt it got a real damp problem. Same was true either way, vented or not.

2nd piece of evidence: RH levels vary through some houses, with a damp area and the rest not. The existence of some air movement between the differing areas doesnt change that. It reduces the difference, but does not eliminate it.

Theory based... air entering from outside carries with it a certain level of water vapour. The RH in the damp room is the result of an equilibrium between vapour ingress or egress and water entry from the cause of the dampness. Adding a dehumidifier will shift that point, reduce RH and increase rate of evaporation.

If youre doing a dry-out after a big flood, you'll get there quicker if you seal it all up, as you can then produce a lower RH. You can also measure water collected. If OTOH youre in a normal living situation, you dont want to seal your house up, and the limited normal level of ventilation doesnt usually prevent the RH being lowered to a useful target by a dehumidifier. If you had the windows wide open that would be pointless, but normal ventilation is within the capability of a domestic size machine to keep Rh down in one room, and the resulting water collection is not affected by a great amount.

NT

[t8769]

Many thanks for the excellent suggestions and information.

The rest of the house is fine, the basement only slightly damp.

Perhaps the best solution would be to have a small fan that blows air from the small basement room into the rest of the hose, thus getting lots of ventallation into the room, but not blowing a lot of air out of the house and costing lost of money for heating.

Its a bit late for tanking, and the damp isn't that bad.

Cheers

[Fash]

Why not use a heat recovery ventilator to the outside. This way you can increase the number of air changes and reduce humidity by bringing in colder air from outside which holds less water. The 'heat recovery' part means having a heat exchanger in the ventilator which warms the outside air coming in using the inside air going out. Do a google search to find suppliers.

Roughly speaking you can triple the ventilation rate without impacting on the heating bill. You can use humidistat controls or timers or whatever. I could put some links but I presume you can google for yourself.

Regards,

Fash

[t8769]

Thanks for the info guys.

As it is only slightly damp, I have a feeling that a fan circulating air to the rest of the house would probably do the trick, but otherwise the heat recovery ventilator sounds ideal

Cheers

[dicegeorge]

Just visited a building which got flooded, they put in a dehumidifier but did it wrong, the roof beams cracked and the ceiling sagged!

they are not happy bunnies

[g]