Ventilation

[Rich C]

This time of year all you will do is bring in cold damp air and make your problem worse.

At this time of year the outside air is actually pretty dry because cold air holds a lot less moisture.

Cold air does hold less moisture of course but we are in the UK, it's wet all year round and the air outside still has plenty of moisture in it during the day. You do not want to bring that into your house.

And yet looking at Fitzroy's numbers above, 100% RH air at 5C when heated to 20C will have a RH of 40%. Why would that be so bad to have in your house?

My house normally sits at 60-70% RH, the kitchen can get higher while cooking. Opening a window dries the air significantly (a couple of hours will get the room down to 50-60% from around 80%).

 

[Rorschach]

Because in the middle of the day the air could be quite warm and as such very wet, but no matter what the RH is by bringing in air from outside you are making your house colder, the moisture will condense and then you bring in colder air again and so on. Then you spend a fortune trying to heat your cold and damp house, all the time bringing in cold air.

 

[John Brown]

So what's your suggested solution, Rorschach?

 

[Rich C]

In the middle of the day today it was 5C... (homer)

 

[Trainee neophyte]

Having just struggled through the wettest November (almost) ever, our house is going black. I am wondering if a small extractor fan would move air from the hot sitting room to the cooler bedrooms/bathroom (all on one level). Or would it pull cold air in from outside, through all the cracks and crannies, and make the house colder? Colder air has less water vapour, and it is less likely for water vapour to condense out if the air is colder than the building, but it is cold...

Moving warm, moist air to a colder room guarantees instant condensation, so could make matters worse.

To remove damp, open all the doors and windows. When I was a youngster, living in a Cornish farmhouse, we never had damp, despite it being Cornwall. We never had heating, either. Frost on the inside of the windows was perfectly normal. If it was windy, the curtains moved, even with the windows shut. In a modern house, this can only happen on curry night.

I am currently trying the cunning plan of running the fire constantly, and keeping bathroom and bedroom doors and windows open. Seems to be working.

 

[Rorschach]

So what's your suggested solution, Rorschach?

I mentioned it earlier. Keep the cold air out, keep the house comfortably warm and run a decent dehumidifier, constantly if required.
If the house is large then an additional fan to move the air around inside might be a good idea.

Doing this means that you keep the air inside dry and you are not wasting money on heating.
We spend a fortune sealing up gaps and insulating houses with double glazing and fibreglass etc in the house, then as soon as someone mentions condensation the first advice to blow all the heat out and replace it with cold air, it's madness.

 

[RogerS]

Environvent. Pulls air from the loft, but has built-in heater for Arctic periods. Output is via a vent in our roof, just above first roof tile. Internal fixings might be easy, but unless you are confident on slates/tiles, I would think carefully about piercing felt and slate/tile replacement. They do this every day and have a van-full of hardware.
If you are in N.E. U.K., around NewKassel (as they pronounce it here), I can give you a contact for this area's rep, one A. Hunter. If not, Head Office is pleasant to deal with; lass there on the 'phones is cogent and intelligent.

Sam

Some confusion here (at least in my head!). Looking at the Environment site there seem to be two types of system. Sammy...is yours a basic one-in-one out device ?

For a whole house, we have (up in the loft but not yet connected ...position 235 on the TUIT list) one that extracts the heat out of the exhaust air and then pumps it back into the house ....which addresses Rorscahs' concern.

 

[John Brown]

Obviously heat recovery ventilation would be the best solution, but from what I've read, it involves loads of ducting, which would be extremely difficult for our house.

 

[RogerS]

Obviously heat recovery ventilation would be the best solution, but from what I've read, it involves loads of ducting, which would be extremely difficult for our house.

Yes...you're bang on the money there. I was fortunate to be doing a whole house renovation back to the bare walls.

I've no idea if MikeG has any suggestions to retro-fit ?

 

[John Brown]

The PIV manufacturer's web sites claim that, in two storey houses, the warmer air at the top of the stairwell mixes with the cold air pushed in from the loft, and this somehow diminishes the cooling effect. Not sure if I can get my head round that, but I just placed a sensor up near the top of the stairwell, and I can see nearly two degrees C compared with the rest of the house.

While I appreciate all the stuff about it being crazy to blow in cold air, I also appreciate that ventilation of some sort is essential.

 

[Petehpkns]

John,

Take a look here if you haven’t.

homebuilding..../how-to-solve-condensation, edited as I don’t have permission to post links, not enough posts I guess....

As my earlier post, stopping/reducing the amount of wet air from kitchens, bathrooms, etc. Then ventilation as you recognise, if you live in older properties then you just accept increased energy bills, or radically alter them by adding insulation.

Pete

 

[Rorschach]

You don't need to spend money on a fancy system for ventilation though, open a window. If you want a through draft then open a window upstairs on the sunny side and downstairs on the shaded side of the house.

Your house will be getting plenty of fresh air from all the leaks and opening the front door etc so I wouldn't worry about it.

 

[SammyQ]

Looking at the Environment site there seem to be two types of system. Sammy...is yours a basic one-in-one out device ?

Yes. The more complex heat recovery system (recycling existing household air) was beyond our budget and, more importantly, my research indicated this version could only achieve its intended efficiency in a new-build, preferably to Passivhaus standards.

As I stated above, we embarked on this with healthy suspicions, quite prepared to be disillusioned and 'have the perishers rip it aht' if the device fell short. Our experience has been quite the opposite. The condensation problem we had, has gone. For that, I am glad, for the health issues referred to earlier.

I am also not so stupid as to think that there will be NO thermal cost repercussions, but given the low wattage of both fans and their low revs, I am hopeful that the overall financial cost will be bearable. My last year's costings arrived yesterday, so ask me this time next December for an objective measurement.

Sam

 

[MikeG.]

PIV is like half a MVHR system, which is what you really should have to solve your problem. The difference is the MVHR systems both draw air into the house, and expel stale air to the outside......but critically, they use a simple heat exchanger to get the heat from the waste outgoing air and transfer that to the incoming fresh air. Thus the incoming fresh air is pre-warmed, and all that expensively produced heat isn't simply pushed out to be replaced by cold air. MVHR will definitely work. It's one of the most important developments at the domestic level in the last 30 years

 

[John Brown]

Thanks, Mike. That's pretty much the conclusion I'd reached. Not sure if the heat recovery option is viable in this property.

 

[Distinterior]

I've installed a good amount of new kitchens in new build houses that have had an MVHR system fitted in them. As Mike stated, they work a treat......The only downside from my own experiences are, the Extractor Hood in the kitchen CAN NOT be ducted to the outside as this would be preferable. It has to be installed in a Recirculation Mode and the cooking fumes recycled back into the kitchen.
I have discussed this matter with various Builders/Architects etc on the individual projects, but they have all advised to recirculate the kitchen extractor fumes.....

So far, all the Clients seem to be happy with the outcome as none of them have come back to me complaining about residual fumes or condensation in the kitchens.
The first project that I came across with an MVHR System fitted was about 6 years ago.....

 

[MikeG.]

..... Not sure if the heat recovery option is viable in this property.

It almost certainly is. There are so many variations on MVHR systems these days that almost anything is achievable. Retro-fit is more awkward than building it into a new property at the right stage of construction, but there is a system out there that would work for you, with no question.

 

[Rorschach]

how much (roughly) would a unit like this cost and what is the payback time?

 

[MikeG.]

I've installed a good amount of new kitchens in new build houses that have had an MVHR system fitted in them. As Mike stated, they work a treat......The only downside from my own experiences are, the Extractor Hood in the kitchen CAN NOT be ducted to the outside as this would be preferable. It has to be installed in a Recirculation Mode and the cooking fumes recycled back into the kitchen.
I have discussed this matter with various Builders/Architects etc on the individual projects, but they have all advised to recirculate the kitchen extractor fumes.....

So far, all the Clients seem to be happy with the outcome as none of them have come back to me complaining about residual fumes or condensation in the kitchens.
The first project that I came across with an MVHR System fitted was about 6 years ago.....

Kitchens almost always have two extract ducts rather than one, and that's plenty for clearing up the air after burning your dinner (there's a boost switch, too for the MVHR for when you burn the sausages. The cooker hood is almost redundant, but helps remove grease from the air.

 

[MikeG.]

how much (roughly) would a unit like this cost and what is the payback time?

It's not so much a unit as a system. It's basically a couple of fans in a plastic box, lots of ducting, and some very basic controls. To buy all the kit to DIY fit in a 4 bed detached property was around £2000 to £2500 when I looked recently. The expensive part comes when you pay someone to crawl around in your loft running the ducts and fitting everything....but for any competent DIYer that should take a couple of days at most. It needs a lot of thinking about, because the pipe runs can be complex.