Besidethewye

I was thinking exhaust air unit on the MVHR output - but sadly it's not one of those and I can't see a way to do it - better than sending a bit of hot air into the MVHR and giving that a small boost.

interesting point on the calculation of standing loss - I don't know the protocol but experience of another hot water tank containing cupboard (even with the lower temperature of a heat pump) suggests a small, sort of sealed room with a modern tank in it gets very warm.

Peter - that's a good point - yes lower temperature which will reduce the standing loss significantly. That takes us in the right direction at least.

Indeed so - thought in mitigation it's a bit of a trade off between being sure that everything is in there with no leaks and covering it up in insulation - and the tank had to go in obstructing pipes behind before we could put water in. It's also very crowded but I did get the plumber to space pipes so they could be lagged so not completely lost. I did wonder about sunamp units but decided against.

Ed - that would be nice - but it's an air source unit with the heat drawn from the outside unit.

Dave - thanks. Yes too late I am afraid. We are hemmed around by all sorts of restrictions in terms of layout and space and the old part is listed and a church so no plant room in there - though the logic is obvious. I will get on it and lag everything in sight (though quite a lot of it is no longer in sight as we keep putting more stuff in there!

JS - thanks - a thoughtful and number-filled reply as ever. We have a rather oversized extract in the room below and I was thinking I could steal some of that - say 10m3/h and live with air being pulled up the stairs on the basis it all sorts itself out via the stair well etc. It's a tiny volume probably no more than 5m3 after allowing for all the kit in there so the extract rate would bear no relation to room size or any ventilation based calculation. I've not tried to do a heat balance and we will bleed heat out through the internal walls possibly rendering the whole exercise futile but if we stagnated 10 degrees warmer then that sort of extract would take out something approaching a kWh a day which ought to be somewhere near what the hot tank is going to lose. Clearly spending time and attention on lagging everything I can makes good sense in there. Maybe it's time for that thermopile I've always wanted to play with dumping heat directly into the MVHR outlet when it's all a bit hot.....

Thanks for that - I suspect you are in a better position with a bigger and open room - otherwise similar amount of kit!

Hi there steadily (if slowly) moving forward and getting close to plasterboarding. We've got a small (3m2) plant room on the middle floor (3 storey) build - the new part including the plant room is designed to be passive house standard. But the old part isn't - so will need heating much more of the time - including a good part of the year when the new part does not. The plant room has the hot tank, heat pump indoor unit, buffer tank, a lot of piping (three heating circuits and associated pumps, one manifold etc etc) and the MVHR unit. I am about to go around and insulate all the pipes I can get to - but that won't be all of them! Because it opens on to the stairs we have to have a firedoor - so no vents. Not switched anything on as yet but have a strong sense it's going to be hot in there. With the tank standing loss, losses from the buffer when that's warm and losses from the pipes even a poorly insulated airing cupboard would get pretty toasty. I am wondering about putting an MVHR extract in there (and rebalancing the rest of the system to cope) - at least that way the air would move and hot air could at least warm the incoming air when it's cold out. Anyone been there and done this - ie small plant room in an airtight, passive house? Thanks

Pete - when I was going around checking, redoing and generally rolling my eyes at the installation one thing I found was that the overgenerous use of silicone (answer to everything) meant that the drain holes at the bottom of one of my doors were all totally plugged. I imagine that if that's a regular event there would be a build up of water somewhere inside the frame?

Thanks Declan - there's not enough space to cover it all up - though we might be able to squeeze 6mm in there (at least mostly). I know that my eye will be drawn to the out of square so you're surely right that this is the time to sort it.

Ah and they told me that they only had satisfied customers.....mine was a one off aberration - odd that

No that's clear - we have a range of degrees of out of true and a variety of spacings around the windows. Been debating how much out of true someone will see - I know I see it even if it's very little but not everyone is quite so critical. Do not get me started on the window fitting.

Alex - it is MBC and yes these windows are fragile as a fragile thing - the window installers left a trail of dings and dents that made it clear just how careful we would have to be. Of course the windows have a certain (and variable) amount of clearance around them back to the reveals so even 10mm would not have guaranteed no overlap anywhere - but it would have gone a long way towards it! Thanks for the advice

Thanks Alex - sadly the tape wanders in an out so much that we can't hide it all - but we may be able to hide some like that! The guys who put up the frame did the taping - it's hardly the first one they've done so not quite sure how it ended up like that.