Old style spur socket

[JohnW2]

Homes are far from being air tight - much tighter than they once were, but they still have lots of leaks. ......... The small air 'leaks' are essential - imagine what life would be like in a fully air tight home.

Indeed. If they were anything approaching 'air tight', extractor fans obviously wouldn't work at all.

So really all an extract fan does is encourage local air to be extracted from a more concentrated point.

Again, indeed - but even though the air extracted is 'local air', it has to be replaced by 'non-local' air (from other parts of the house) - which, in turn, has to be replaced by (cold') air from outside of the house, via whatever ventilation/ 'air leaks' exist. As above, in the absence of such leaks, no extractor fan in the house could work

I would suggest your 'substantial' is a massive exaggeration of the true situation.

That's where we appear to disagree.

Kind Regards, John

 

[JohnW2]

I would suggest your 'substantial' is a massive exaggeration of the true situation.

I should perhaps have added .....

I think the most one could reasonably hope for would be complete and immediate mixing ('dilution') of the incoming (cold) air with the entirety of the house's content of (heated) air. Hence, if outside and initial internal temps were, say, 12 °C and 22 °C, then the best one could probably really hope for if 216 m³ of air was extracted from a 216 m³ house would be that the internal temp would fall 'only' to the average of those temps, namely 17 °C.

If the heating system could not 'keep up' with that heat loss, temp would gradually fall further, as more cold air was drawn in.

Kind Regards, John

 

[Harry Bloomfield]

I think the most one could reasonably hope for would be complete and immediate mixing ('dilution') of the incoming (cold) air with the entirety of the house's content of (heated) air. Hence, if outside and initial internal temps were, say, 12 °C and 22 °C, then the best one could probably really hope for if 216 m³ of air was extracted from a 216 m³ house would be that the internal temp would fall 'only' to the average of those temps, namely 17 °C.

I still say that is a massive exaggeration of the true picture and would be very noticeable.

Also don't forget that a fairly large proportion of the heat you feed into your home, is stored by the fabric itself, separately from the air. Remember how difficult it was, just a few weeks ago, to cool a home down? Upstairs windows wide open to the night air, in attempts to cool the fabric down.

 

[JohnW2]

I still say that is a massive exaggeration of the true picture and would be very noticeable.

Yes, one would expect that. However, we're talking about basic Laws of Physics - so if we are getting 'the wrong answers', it must be that are assumptions are incorrect. The possibilities which come to mind are:

1... Extractor fans are often run for relatively short periods, hence the amount of cold air they suck in from outside is only a small proportion of the house volume.
AND/OR
2... The extraction flow rates usually achieved are a lot lower than we think (hence a lot lower than guidelines). That could be due to one or more of a number of causes:
2(a)... Out-of-spec (or untrue spec!) fans, and/or
2(b)... Flow rate restricted by extraction through non-ideal ducting, and/or
2(c)... (perhaps the most likely) in relatively 'air-tight' houses, limited ventilation impairing the fan's ability to extract.

[why, I wonder, does the new forum software not provide a facility for indenting and/or numbered/bulleted lists? ]

Also don't forget that a fairly large proportion of the heat you feed into your home, is stored by the fabric itself, separately from the air.

True - but, again, I would think that would be "very noticeable", since if one filled a ('warm fabric') house with cold air, it would take an appreciable time for the fabric of the house to warm it.

Kind Regards, John

 

[SUNRAY]

Using a temterature sensor at the extract/exhaust position is a common method of measuring the space temperature.

Which would be rather pointless if placed at the exhaust of a cooker hood

Indeed you are correct, however measuring the extract (usually not exhaust) temperature is an extremely common system used in air managed systems.
The point you correctly make is no different to ensuring a room thermostat is in the correct place.

I was sent to do some faultfinding in a retirement complex after NSH's were replaced with wet rediators working via metered heat exchanger for each flat. The complaint right the way along one side of a corridor was the living room was cold but turning the 'thermostat' up to 26-28°C meant the bedroom was baking but bedroom rad couldn't be turned down far enough.

The original assumption being the rads were incorrectly sized.

However the heat exchanger was fitted in place of the hot water cylinder in the little hall with a rad the other side of the uninsuated plasterboard wall and the stat on another wall in the hall:

I walked into the first flat and felt the wall beside the stat, I didn't bother checking anything else but moved on to 2 more identical flats.
I cobbled one stat into the lounge for a few days and againts all predictions the rads became balancable.
My report simply stated the stats were in the wrong place and the contractors should return and move them to an appropriate location.

 

[JohnW2]

Indeed you are correct, however measuring the extract (usually not exhaust) temperature is an extremely common system used in air managed systems.

That may well be true in terms of heating/cooling systems, but it surely is not particularly relevant in the case (which we are discussing) of extractors being used to remove moist/smelly air (in an ideal world, without any change in temp), would it?

Kind Regards, John

 

[SUNRAY]

That may well be true in terms of heating/cooling systems, but it surely is not particularly relevant in the case (which we are discussing) of extractors being used to remove moist/smelly air (in an ideal world, without any change in temp), would it?

Kind Regards, John

It wasn't me who mentioned heat loss first

 

[JohnW2]

It wasn't me who mentioned heat loss first

I realise that, but I thought that, for the benefit of anyone who might subsequently be crazy/brave enough to plough through this thread, that that particular exchange between Harry and yourself really has nothing to do with extractor fans (and, of course, even less to do with the title of this thread )

Kind Regards, John

 

[SUNRAY]

I realise that, but I thought that, for the benefit of anyone who might subsequently be crazy/brave enough to plough through this thread, that that particular exchange between Harry and yourself really has nothing to do with extractor fans (and, of course, even less to do with the title of this thread )

Kind Regards, John

But it is much to do with air flow and my deviation with the retirement home may assist with demonstrating that the air in a space isn't consistant across that space.

 

[JohnW2]

But it is much to do with air flow and my deviation with the retirement home may assist with demonstrating that the air in a space isn't consistant across that space.

I don't disagree with that.

It perhaps reinforces what I've been saying - that when an extractor moves (heated) 'local air' from kitchen/bathroom into the outside world, that air movement will usually be 'followed by' cold outside air being sucked into other parts of the house as a consequence, long before the 'local (heated) air' (which is being extracted) knows anything about cold outside air being sucked into other parts of the house

Kind Regards, John