Ceiling vent at top of stairwell?

[MJNewton]

I am planning a retrofit installation of an MVHR system to our "2.5 storey" (i.e. the top floor is half in the roof space) 2007 house, and the current plan for the system layout is here.

 

I am wondering whether to fit a ceiling vent at the top of the top-floor stairwell (indicated on the drawing by the blue question mark) to help reduce the effects of stratification? Certainly in the summer months a fair amount of heat collects up there and is much warmer than the lower floors and so some active cooling (or at least freshening) of that air could be advantageous. Whilst I haven't noticed an obvious temperature differential when the heating is on during the colder months I can't help but feel that there must be warm air sitting up there.

 

With MVHR I'm thinking I might end up with something of a 'dead spot' in this location as there is no obvious air pathway between a supply and extract vent from what I can tell without the inclusion of a vent. Might it therefore be worthwhile? If so, supply or extract? I am leaning towards supply given it's more of a living space than a wet room, however extract could be beneficial based on the fact that in the winter I could be recovering some of the heat up there, and in the summer could be extracting it out of the house (with the bypass on hence no recovery).

 

What does the panel think? Happy to receive comments on any other aspect of the proposed design too.

Edited April 5, 2018 by MJNewton

[MJNewton]

Not the most popular posts this one! ? Nevertheless, I thought I'd follow up with my conclusion in case it is food for thought for others that may find themselves in a similar quandary.

 

What I have decided to do is *not* put a vent at the top of the top stairwell. The reason being is that my planned flow rates (on boost) for the top floor are: en suite extract 8 L/s, master bedroom and dressing room supplies 5.8 L/s each. Thus, there should be a net positive supply (11.6 compared with 6) which should therefore result in air flow out through the stairwell thus in turn eliminate the dead spot I was concerned about.

 

Of course, this theory is wonderfully simplistic but it's all I can go on until the system is installed at which point I could always add a vent if need be or, most likely, just live happily with the as-planned system!

[Cpd]

I am putting an extract at the top of my stairwell as it’s all open plan downstairs and even with a kitchen extractor / carbon recycler the stairwell  is a dead spot and I would like to capture any cooking smells before they make it upstairs to the bedrooms. Am getting closer to the point where my vague plans need to be put into action..... 

[MJNewton]

I suppose every house/layout is different, and indeed we all might have slightly different priorities and preferences over what matters most.

 

I know what you mean about the putting plans into action. I'm sure when it's all done I'll have spent more time planning than doing, and that's despite mine being a retrofit which throws up challenges all of itself!

Edited May 16, 2018 by MJNewton

[Jeremy Harris]

I took the precaution of fitting a fresh air inlet immediately above the entrance to the kitchen/dining area.  The utility and downstairs WC come off the kitchen/dining area, so overall we have a lot of extract moving air away from the rest of the house, and adding a fresh air inlet tends to force airflow away from the stairwell and down and out through the extracts.  I did this because I was concerned about cooking smells going up the stairwell, and it seems to work.

 

I think putting an extract in the stairwell would encourage air from downstairs to rise even more than it would tend to do anyway, so may make things worse, whereas feeding fresh air in at the top of the stairwell may well encourage air to flow back down to the kitchen extract.

[Cpd]

23 hours ago, JSHarris said:

I think putting an extract in the stairwell would encourage air from downstairs to rise even more than it would tend to do anyway, so may make things worse, whereas feeding fresh air in at the top of the stairwell may well encourage air to flow back down to the kitchen extract.

 

This does make sense and I will take it on board, I could close of the stair sides that face the kitchen and this would go a long way to prevent the air from the stairwell supply short pathing to the kitchen extract. There would then be a supply at the very far end of the room above the fireplace and a double extract in the kitchen.   The whole downstairs is only 40.85m2 with a total volume of 97.07m3. I like the idea previously talked about of putting an extract in the bin cupboard.