Just bought a portable air con unit, and wonder if instead of venting it thru a window, I can vent it do the loft of the house. I have planned on putting the vent pipe thru' a bit of perspex so I can then put the perspex across the open window and create a good seal and stop outside warm air getting back in, when I came up with this loft idea. Sure, the hot air will get into the loft, but it's boiling up there in summer anyway.
This air will be warm and damp (from the condesate on the cooler). The warm air isn't a problem but the damp is not so good. How about fitting a vent into the eaves and venting directly outside but via the roof space for the duct work?
Ah -- there's a flaw there. If you stop the outside air coming back in, either the aircon unit won't be able to blow hot air out, or the walls and ceiling/roof of the house will implode as a vacuum develops in the house;-)
OTOH, if you let the outside air back in, the aircon doesn't work very well as it's fighting itself cooling the hot air which it's sucking in.
Notice that of these two options, neither works very well, which explains why that type of aircon unit doesn't work very well.
If the loft is very well insulated and airtight to the rest of the house, I see no harm in it if there's nothing up there which minds being cooked). Otherwise, you'll just increase the heat radiated back from the ceiling and/or the amount of hot air which is sucked back from the loft into the house.
I was given one of these by another family member who bought it before realising they don't work. This one has a separate air inlet grille for the air which is blown out of the house, from the air inlet grille for the cold air blown into the room. I was able to make it work quite well by sealing off the former to a second hose which goes outside to suck air directly into the unit. That way the inside air is just recirculating. Most of these units don't have separate air intakes for the two air paths though, so you can't do this.
Blowing damp air into loft is a definate no no, the moisture will condense on things eventually leading to rot. You need to vent to the outside world.
Also as my mate found out there is a fairly restrictive limit to the amount of pipe it will push waste air tthrough, his was quoted 3m, which he ignored.
Anyway ignoring this he plumbed the vent pipe into loft and across a bit of loft and out through sofit. Couple of issues, the cooled air flow went from crap to extremely crap as he was now venting along about 6m of pipe and also when turned, off moisture condensed in the pipe, eventally ran back down into the unit and flooded his bedroom floor !!
Anyway £1500 later got a professionally fitted two part air-conditioner that does the job properly and silently in the bedroom, enough so it can be left on at night.
On Tue, 20 May 2008 15:23:37 +0100 someone who may be "Ian_m" wrote this:-
One of the reasons why sensible people put drains at the bottom of rising ducts which carry humid air.
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