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.

Thanks all - a few things to try.... Sadly it's been on a good while for a variety of reasons that I won't go too far into. Attached a couple of pictures. We did try peeling it back and scraping off the glue - but it was such fun that is what sent me to the forum.... Windows are prefinished and it feels pretty vulnerable As an aside it's hard not to worry about relying on the tape - it's surprisingly easy to put holes in it - in particular where it's stretched across corners - I made the mistake of running my finger along one area and left a nice cut along the length with my nail (and the nail is more building site than catwalk).

Hi there just in the process of putting plasterboard in the window reveals and finding that the taping is somewhat variable.... In some places the tape will be hidden by plasterboard but in most it sticks out well beyond the board. Some of it might disappear behind skim but I am not sure how well that would work on tape. We don't have the space to put another board on without fouling the window opening (inwards). Is there a foolproof technique to cut back the tape that's generously stuck to the wooden (pre-finished) window frames and clean away the very sticky residues? Appreciate any advice (other than make them more careful with the application of the tape which is true but redundant) Cheers

I thought I had a plan and now I am not so sure! We have extracts about 2m from the hob one way and another in the utility about 3m the other but a possible route out of the kitchen and into the corridor/upstairs drawn by the extract in the toilet.....we don't fry a great deal though the better half does note that my repertoire in the kitchen is dominated by stir fries of various and unrepeatable mixtures. My aversion to a) having to make modifications later and b) finding gunk in the extract pipework which I can't see how we would ever clean out makes me think putting a recirc hood in now would be easier and my wish not to keep burning money unnecessarily suggests put the mounting in and move on.... I'll check with the boss for the definitive answer. As they keep saying by the time I get onto my third house I might have it all down to a T

Thanks Scottishjohn - I share your worry about keeping the MVHR clean. Hopefully a recirculating system would do the trick without opening another route to outside. I am past the point of putting any more holes in the walls!

Thanks all - much appreciated.

We have an island that will have an induction hob in it. Going around the circle of extraction (recirculating rather than venting) and not sure where to stop. The house is passive with MVHR and an extract in the kitchen ceiling about 1.5m to the side of the hob location. We've mainly had houses with no extract/hood and never worried - but they have always been leaky in comparison (cold and old). I was going to leave a cable and space in the ceiling so I could fit a ceiling mounted unit if we need it. But wondering about either a suspended recirculation unit or integrated hob unit with down draught. I don't want to fill the MVHR up with grease if we can help it - and we don't do a great deal of frying - but someone might or our new diet might switch to chips.... We have friends who built a passive house recently - started with no extract but came back to get one - but their MVHR looks a bit odd to me - one vent in the open plan kitchen diner that's maybe 20 feet from the hob (and only one in the whole room - which I assume, but don't know, is extract rather than supply). I am sure this loop has been gone round a few times but couldn't find much with my searching. Appreciate any experience.

Thanks for that - quick and on point as ever! Nick - why the additional layer of plywood over the caber deck? Is that just to get an even surface and better adhesion? I'll get in and scrub the undersides..... Thanks

Apologies if this is a repeat - couldn't find anything with a search. We have three shower trays to fit to a caber deck wooden floor. Two are 40mm deep and I see no great problem in fixing down. The other is only 25mm deep and large (1700 by 900) all stone resin. The instructions for the big tray say a bed of 15mm deep sand and cement. Not all that convinced by sand and cement on a timber floor. Wondering whether a flexible tile adhesive or even the spare sika floor adhesive we have might work better - staying flexible, filling the gaps and not so much at risk crumbling over time. Any advice?

Thanks again Dave - sounds like we should be ok! The heat pump circulates to the buffer tank so should be fine and if the pumps are ok we should be good to go.

Dave - thanks for that. It is an ASHP. The wiring centres switch a pump and give the call for heat - but they don't incorporate a time delay to switch the pump on once the actuators have opened. It was avoiding the pumps working against a closed circuit that was the reason to ask about time delay relays. So the issue is whether a bypass pressure relief valve to allow the pump to circulate in the time that the actuators take to open is ok or whether at time delay relay makes more sense or whether we do both (or neither!). The heat pump supplier recommended the non-return valves rather than the two port valves - apologies if adding the background just confused the issue.