Hello,

I am buying my Council flat which has a history of mould and poor ventilation. I am planning to fit a MVHR unit to solve the mould and help reduce heating costs.

I want to save money, being poor and was hopping to fit it myself. Getting it commissioned (balanced) afterwards.

I have designed the system in my head, looking at as many recommendations and building regulations as a good novice might.

The problem being I need to get permission from the Freeholder (the Council). I will need to submit a design and specifications to meet an unknown standard. This is going to cost more I know.

So my two questions as it stands are...What is the best way forward ? I guess I need to find someone to design as well as commission the unit. But I have a clear idea what I want and will only need a few pointers. Or do I just find someone who can commission it and agree my basic plans ? Any recommendations, I'm in South London ?

The other question I have is regarding my design. I have a choice between venting the unit "on the same level as the intake", through an already cut window or by using a redundant chimney. The redundant chimney is from an old 'hot air system' and is substantial and there will be no danger of moisture coming back into the unit. I was hopping to use the chimney as it has a passive suck to it which will aid the fans. Yet at the same time, will it make it impossible to balance and commission the system to any standard ?

I'll planning to fit a Nuair unit (MRXBOX95B-WM1 ) to a well sealed concrete flat, about 50m2 in total.
Cost of unit MRXBOX95B-WM1 is £575 + 4% carriage + VAT = £717.60
With ridged piping throughout and making good, I expect to pay no more than £1500 in total, if I can 'do it myself'.

I was hoping any design and commissioning will not add too much to this, someone has quoted me a lot to commission it after seeing plans and calculations; which I may not be able to do to any real standard.

Any advise or comments more than welcome. Thanks

Thanks.
I will try and get something agreed, I've already let the cat out of the bag by asking.
I should be able to satisfy Building Controls who seem to only want to make sure that the unit is compliant and it is big enough for the job and therefore the Freeholder should be happy(figures crossed). I will report back with the hoops I had to jump through.

For intake I was going to remove a fan in the kitchen which has a hole going straight out, the chimney goes up another 3 floors and like I say has a good suck on it. I'd welcome any other comments on using the chimney.

The box will have to go in a cupboard but I've a good one, away from the bedroom and living room which will do nicely.

I do plan to continue to insulate, I've a couple more rooms where I need to line the old solid walls which do loose heat. But one thing at a time and the mould needs attention.

Here is a scale plan.

Please note the chimney !
I am still concerned about designing with using the chimney as I wonder if this will make it impossible to balance.

Any other advise, I know I should not supply over doors but they are existing holes from old 'hot air' system and it will save loads of time and effort .


Here's me trying and do the calculations, although I'm a bit clueless.

It seems to me that I need 13 L/S for the Kitchen
plus 8 L/S for the bathroom. Equals 21 L/S for boost speed.

Now I'd only need (50m3 x 0.3) 15 L/S at normal speed.

So it would be 15 L/S split between the two in's and out's at normal speed.
and 21 L/S split for boost speed.

Any advise?
Would anyone what to do the commissioning for me ? I'd pay what I could and it should be an easy small job.

Echo concern about chimney exhaust. If the MVHR is doing it's job the exhaust air will be cold, so there will be no suck anymore. The cold air travelling up 3 floors of chimney will ensure this chimney is kept chilly too.

Thanks.

So it seems that most people think that the chimney is a bad idea.

Since there would be a low temperature difference the suck will be greatly reduced.
I would then be left with a possible problems of a chilled flume which will attract moister.

Is that right?
Sorry don't want to let go of some ideas. I would therefore have to vent out the bathroom window which has a fan in it at the moment. Will this be another problem in it's self ? Was hoping not to have to cover any of the window but should be able to box the corner where it will go out. Again any comments welcome.


I guess I'll be waiting for a blue moon for the Council to agree so Yes might well be able to wait for you to come to the big smoke.

EDIT.
With it working at about 90% there will be a 1 or 2 degree difference it the air at the bottom and the air at the top of the chimney so it would still such up and out.

The left of the flat is not outside.

I have changed the design now without the flume. Now I have a choice which one I use for in and out of the building. The window or the hole in the wall. I was thinking I might swap them if I abandon the flume so each fan is working more evenly.

I can put the vents up the middle of the hall just I will need to box them in so loose more space. Was thinking with such a small system it will not make too much difference. But I've no real experience.

Still concerned about using the window, although it would stop me having to replace the double glazed glass, which has a hole for a fan in it.

The problem I have it its a second floor flat and cutting any new whole in the external walls will be too much of an effort for any real benefit from all this work. Cost basically of scaffolding etc. And Freeholder would freak.

So I have a whole cut in the kitchen wall and boiler being on the other side of the kitchen window.
The other existing out is the hole in the bathroom window. Or the flume.

three floors up ?

There's also no space on bathroom wall. The window is long and thin, high up, all the way along the outside wall.

Thanks though.

So this is a tidy solution. Thanks "slidersx200"

Cons.
1. Does not use flume. (unless somebody wants to back the flume idea I guess I'll have to let go of it. )
2. Difficult to service unit. but not impossible. and more noise transfer from that wall.
3. More bends then ideal, but thats retro fitting.

Right ! I'll forget it for a while... and my mind will start to settle.
Thanks for all the pointers.
Still unsure about calculations...

Don't need resistance calcs. Install as well as poss for retrofit, minimize run lengths and bends, use rigid ducting wherever possible. The commissioning will sort the rest as the terminals can be adjusted to give required flow rates.
The chimney is a red herring. Use the window if it means the difference between installing and not. You can change this later if someone is not happy. Get that bathroom window upgraded and whilst it is out, core drill for the exhaust duct. Or reduce the size of the new window leaving room for the duct next to it, fill not drill?

Thanks Finny.

Are you saying 'do not use chimney no matter' or are you saying 'use it if you can' ?

Else I'm feeling a bit more confident. Thanks.

The minimum total flow rate to deliver 0.3ach is 38m3/h, the maximum you are ever likely to need is 100m3/h so the normal could be anywhere in between depending on number of occupants and how they behave.

To maintain good air quality in a bedroom while you are sleeping normally requires 15.4m3/h per person. My calcs gave 34.7m3/h to the bedroom at normal mode so not much above that recommendation, assuming 2 people in there.

Depending on how airtight the flat is and how well the air can transition between spaces there might not be much need for worry given the total volume anyway.

PS my last post should have read "if you can't run both ducts to outside through the bathoom the unit is probably better facing the way you had it before."

Yes. Ready to go, almost !
I've added silencers to supply.

Yes I'll go with 125mm as it is what the unit takes.

So I've added the rates to plan for the BCO. Also some ratios with a total supply of about 51m3/h for myself to get 0.42ach.

Will have to wait a little for an OK from Freeholder and will need to think about the practicalities of using the window and how I'll make it work. But will keep you informed.

Thanks again.

So I'll be finished this weekend.

Managed to get commissioning agreed for £150.

I was going over the flow rates and have been using the numbers "slidersx200" gave me above.
Now he split the extraction from the kitchen and bathroom 40% and 60%, where as the space is a 30% 70% split. Did he just make an error, or am I meant to supply more to bathroom than kitchen in relation to their size?

Thank for any help, would like to set it up before commissioning.

Hi , slider , got any link to good simple info on how to do these calcs. recommend rate etc.
thanks ,
Just got hold of a 2nd hand ventaxia sentinel unit so think of upgrading my little 2 room sys. to whole house.
cheers Jim