Coanda

All the air that's in your flat has come from the outside, so bringing in more will just be the same level of pollution. You say it is well ventilated already so whats the point, unless you can filter the incoming?

I set my DIY system up with one I got on a well known online auction site. How accurate does it need to be?

I'm wondering, does any air get sucked in through the condensate drain?

Yip. My bin blew over and a fence that was falling down is now down. To be fair it was as bad as I've seen in a long time.

I'm pretty new on the mvhr scene and while I am researching, I am running a temporary set up which is not powerful enough, but better than nothing. My house, I thought was quite leaky but RH and co2 levels were much higher than they should have been so obviously more air was needed. I think my mvhr won't have to work as hard as one in a tighter house, but is still necessary.

I had the bucket left over from drilling the ceiling holes. I put my hand up through the hole with a sealer and held the drill inside while I drilled the holes, the bucket caught the dust.

I balanced mine up with the aid of an anemometer bought off ebay, a plastic bucket with a hole cut in the bottom and a sponge seal around the top. I had to add a speed controller to one of the fans as it was more powerful than the other. I wasn't too difficult. I've got some mods to do so I'll be doing it all again soon.

So far there has been no condensation in my DIY unit. However, I am in the design stage of DIY unit 1.1 which will be a much better insulated twin core model. Am I right in thinking, should any condensation form, it will be in the extract (from home) chamber and that is where I should put a drain? Just in case.

I wouldn't recommend it. I had a large GSD which was mostly a yard dog when not competing. A few years back during a heavy frost SWMBO decided to bring him into the house, "Poor thing is cold" she said. Bed time came and she decided it was still too cold for him to go outside, and the cat claims the living room, so he was permitted to sleep on the bedroom floor. He never settled all night, sniffing snorting, farting , moving back and forth. I said to her in the morning, "We won't be doing that again", she didn't disagree.

If there's a flow through the building of x m3 doesn't it follow that there must x m3 coming in and x m3 going out or am I missing something?

I Took a oic this morning. Which gives SAP 73.6% PHI 76.9% I adjusted the incoming air to within 2,5% of each other. Life is to short to strive for better. I left things for a few hours and took another. Which gives SAP 71.2% PHI 80.8% Making the SAP findings a bit lower and the PHI findings a bit higher. Is it better or worse?

I know that my input exceeds the output by maybe 20% but I bought a speed controller for the faster fan. So that's a job for tomorrow. But the formula doesn't know that input air is more than output so it's the same for both.

What I think is skewing it is that intake temp is higher than exhaust because of the heat on the south facing roof. If we take yesterdays figures of intake 0.4 exhaust 3, supply 7.9 and extract 10.6. 7.9-0.4=7.5 and 10.6-0.4=10.2. 7.5/10.2=73.5% for SAP and 10.6-3=7.6 and 10.6-0.4=10.2 7.6/10.2=74.5% If the formula was correct you'd expect similar results over a range of readings. No?

Have i got this right. Using todays figures 13.4-12.1=1.3. 14.4-12.1= 2.3. 1.3/2.3= 56.5% 14.4-10.6=3.8 14.4-12.1= 2.3 3.8/2.3=165.2% Hellova difference.

Nothing has been changed, it's just that it's a lovely sunny day here and the intake is on the south facing roof side. I've been reading here to try and get my head round this % thing. Cheap MVHR or expensive MVHR? The science behind Heat Exchanger Efficiency - Heat, Space and Light Ltd (heatspaceandlight.com) Why different methods. I mean 2 and 2 is 4 but apparently not in this case.

Thank you for pointing that out, no point deluding myself. I wrongly figured because the intake was warmer than the exhaust, it had to be good.

Very pleased with my set up today. The numbers are. intake 12.1c exhaust 10.6c supply to house 13.4c extract from house 14.4c Sun is shining on the back of the house where the intake is. That has to be a good percentage no matter how you count it.

BPC. But it's only free if you buy from them, which means they have it built into their pricing structure. You pay a deposit which is not refundable but offset against a purchase. Nothing in this life is free.

On a factory built MVHR unit with boost mode etc. Lets say it's set up to boost when RH in the bathroom reaches 70%. So I'm enjoying my shower washing away the dirt and troubles of the day, and RH hit's the magic 70%. Is it just the extract fan that goes to boost, or does incoming air increase as well?

Does anyone have any info/opinion on this machine?

I would ask why they are supplying an over size unit. Wouldn't that be like putting in a proper size unit and running it on boost all the time. Who would want to do that. Plus it's likely more spendy than the correct size.

Lots of people here with a lot more experience than me will be along shortly, in the meantime I'll give you my recent experience. My bungalow was built around 1935 they tell me. I moved in about 5 yrs ago to draughty sash windows leaky wooden floors over a crawl space and virtually no insulation. It was cold but dry. So in goes double glazing, floors sealed up and lots of insulation. Next comes high RF which first showed up as black mould in the bathroom. I installed better extraction, wiped down the shower after every use and bought a dehumidifier. This brought the humidity to bearable levels. I heard about mvhr and did some investigation, turns out Co2 levels are a cause for concern in our modern tight homes. I bought Co2 and RF meters and was astounded by the high levels. I did a DIY installation of mvhr and in one week the change is noticeable. While I was figuring out and installing the system I left the dehumidifier and fans off two weeks. Co2 in the living room and bedrooms with two occupants was well over 2000, I think maybe 2400. The RF was regularly over 70% sometimes over 80% and one morning 94% After one week of running my system, which is btw underpowered, but better fans are coming, Co2 is down to 1084 this morning and RH was 67. A considerable improvement which I think will improve more as the house dries out.

Sorry, you're way over my head now.

I was quite pleased with my first diy attempt, so now I'm planning version 1.1. Planning to add an extra core as well as streamlining the enclosure. I haven't seen it discussed anywhere so I'm wondering is it better to suck the air through the core(s) or blow, or is there no difference? I know the effects of a fan blowing can be felt much further than suction from the same fan.

Pardon my dimness, but isn't the difference between a Cubic metre per hour and M3h about the same as the difference between a ML and a CC?