Philxyz

Yes this is very impressive

OK, thanks Iceverge. Has your system been running long?

Is it worth the extra money to buy semi-rigid ducting with "Anti-Microbial and Anti-Static additives"? In my case, for a 100m2 cottage with 3 people occupancy. I need to choose between the Ubbink ducting with or without: AE48C Semi-Rigid Duct Anti-Microbial & Anti-Static 50m AE48C Semi-Rigid Duct 50m Thanks, Phil

What makes a decent roof terminal for a wet and windy location? I can't find any claiming to be better in wind which surprises me. For a pitched tile roof. The terminals will be on same side, 2m apart, and no closer than 1m to edge. 150mm ducting (Aerform). Is a low profile necessarily better in wind? These are two I am considering but with little confidence in selection: Low profile Verbas Slate £74 Chimney Ubbink UB47 Insulated £116

Great info. M5 is good enough for me. Thanks John.

I am about to buy an MVHR system. Largely driven by the need for side connections, I have whittled down to two units: Name Filters Spigots Vent Axia Plus B G4 & M5 Top and/or side Airflow DV300 Entro 2*G4 & F7 Side The location is rural and pollen filtering is very important to us. I would get the Vent-Axia but it doesn't have an F7 filter. So maybe the DV300. Can you help with any of these three questions: Is there a noticeable difference between M5 and F7 filters for reducing pollen? is the DV300 any good? I haven't found any comments or reviews. Can you recommend a unit >230m3/h, side spigot connections and F7 filter? Thanks

Putting together a parts list, and I cannot find install info for these Coanda grills. How close should they be to the ceiling? Can I connect these straight to a duct (eg in my case to a AE48C Bend 90°)? I am on a steep learning curve and trying to minimise my questions here. Just tell me when you've had enough John!

John, thanks again. You've been more than generous with your time and knowledge. I am going to do it myself.

In fact there is a mezzanine above the bathroom and bedroom 2. It will be used for utility and storage (the MVHR unit for example). Not a living arera but will be regularly accessed. Is it worth moving that supply vent onto the mezzanine?

Having got a design I now think I may install it myself. Maybe you would comment on my vent positions (see attached image). These are currently more positioned for ease of install. I suspect the far end away from the vent in Bedroom 1 might be lacking flow. How do they look to you?

Fantastic. Thanks very much for your great help John. And thanks to others.

OK, putting together what I've learnt on this thread: Area Extract m3/h Supply m3/h Extract ducts Supply ducts Kitchen/living 60 48 1 1 Bathroom 48 1 Bedroom 1 40 1 Bedroom 2 20 1 TOTAL 108 108 2 3 Most erroneous duct run @ 60m3/h air flow rate: Drop per meter = 3.9Pa here Drop per 90° bend = 7.6Pa here Drop Plenum = 10.1Pa here Drop dbox = 5Pa here 5m length + 2 bends + plenum + dbox = (5 * 3.9) + (2 * 7.6) + 10.1 + 5 = 49.8Pa (<100 so OK) Requirements: 90mm ducting (eg Ubbink Air Excellence) Coanda effect supply vents (eg Zehnder) MVHR unit with a flow rate of at least 216m3/h (eg Zehnder ComfoAir 350) How does that all look?

Thanks for bearing with me. Below I try to follow your steps as best I can but I am not quite there and have more questions: Straight from your chart I enter 47m3/h and 29m3/h for the kitchen and bathroom extractions respectively This gives a total of 76m3/h for extraction The bedrooms is less clear. Your chart says "2bed/3 person: 61m3/h". So I enter 30.5m3/h supply for each bedroom. Is this correct? To bring the supply up to equal the extraction I add a 15m3/h supply into the living area of the open plan kitchen/living. Area Extract m3/h Supply m3/h Kitchen/living 47 15 Bathroom 29 Bedroom 1 30.5 Bedroom 2 30.5 TOTAL 76 76 Is this room flow rates table OK? The total reached of 76m3/h is well below the whole house flow rate (91m2 * 1.08) of 98.28m3/h. Don't I need to raise both extract and supply up to reach the whole house rate? What is 'your normal flow rate for that duct'? I don't know what that means. Where do I get it, or how do I calculate it? Thanks very much for your time.

OK, this I do not quite understand. I'll explain my calculations and perhaps you will be kind enough to point out where I am wrong. Whole house air flow The min requirements for kitchen/bathroom/bedroom are lower than m2 by .3 so I use the latter. 91m2 * 0.3 = 27.3l/s = 98.28m3/h = [99m3/h] Calculations at 35m3/h per duct Area Floor m2 Floor*.3 m3/h Extract m3/h Supply m3/h Extract ducts Supply ducts Kitchen/living 42 45.36 70 35 2 1 Bathroom 8 8.64 35 1 Bedroom 12 12.96 35 1 Office/bed 29 31.32 35 1 TOTAL 91 [99] 105 105 3 3 Pressure drop using Ubbink 90mm ducting Drop per meter = 1.3Pa here Drop per 90° bend = 2.6Pa here Drop Plenum = 3.5Pa here Drop dbox = 5Pa here 5m length + 2 bends + plenum + dbox = (5 * 1.3) + (2 * 2.6) + 3.5 + 5 = 20.2Pa Ah. OK I think the penny may have dropped as I write this out. My calculations above have a very low pressure drop. Should I readjust my calculations to have a higher flow rate whilst keeping Pa < 100? Let me try that now. The largest single room requirement is the kitchen (45.36m3/h) so I will use 50m3/h. Calculations at 50m3/h per duct Area Floor m2 Floor*.3 m3/h Extract m3/h Supply m3/h Extract ducts Supply ducts Kitchen/living 42 45.36 50 1 Bathroom 8 8.64 50 1 Bedroom 12 12.96 50 1 Office/bed 29 31.32 50 1 TOTAL 91 [99] 100 100 2 2 Pressure drop using Ubbink 90mm ducting Drop per meter = 2.7Pa here Drop per 90° bend = 5.2Pa here Drop Plenum = 7Pa here Drop dbox = 5Pa here 5m length + 2 bends + plenum + dbox = (5 * 2.7) + (2 * 5.2) + 7 + 5 = 35.9Pa To summarise: both these calculations would work. The 35m3/h system has a massive headroom and uses more ducting than needed. The 50m3/h system has less but adequate headroom and uses fewer ducts. Go with the 50m3/h system. Is this correct?

I have calculated for my most difficult run (all the others are very simple of a few meters and a plenum) Pressure drop calculation For Ubbink Air Excellence 90mm ducting @40m3/h Drop per meter = 1.7Pa here Drop per 90° bend = 3.4Pa here Drop Plenum = 4.5Pa here Drop dbox = 5Pa here My most difficult duct run: 5m length + 2 bends + plenum + dbox = (5 * 1.7) + (2 * 3.4) + 4.5 + 5 = 24.8Pa But now what do I do with this? I presume it should inform my calculations of ducts per room but I cannot quite get my head around how! Advise appreciated. Thanks.

That is very helpful thanks Kelvin. John and Mike, thanks very much for the PDF and thread link. I will respond later after some reading.

Thanks JohnMo. The kitchen/living is one room. I was working on the idea that it is not good practice to have supply and extract in the same room. Is that wrong? Could I have extraction on the kitchen side and supply on the far end of the room? I suspected this was over doing the amount of ducting but figured that being cautious and over engineering would allow low flow rates down each duct. One of the specifications I have been quoted had way more ducts. Others had less. My shot here falls in between.

After some wildly differing MVHR specifications/quotes I have attempted some basic calculations myself and wonder if they're of any use to help me choose installers. It's a small cottage (91m2) of four rooms: kitchen/living, bathroom, bedroom, office/bedroom. It will be airtight. To calculate the whole house l/s flow rate I multiplied total m2 floor space by 0.3: 91 * 0.3 = 27.3. Rounding up, I reached a whole house flow rate of 30l/s. At 5l/s per duct* this means 6 supply ducts and 6 extract ducts. Area Floor m2 l/s(floor*.3) Target l/s No. ducts Kitchen/living 42 12.6 20 4 extract Bathroom 8 2.4 10 2 extract Bedroom 12 3.6 15 3 supply Office/bed 29 8.7 15 3 supply TOTAL 91 27.3 30 6 extract/supply *I have not attempted to calculate ducting resistance. Instead I have simply calculated using a 5l/s flow rate for 75mm semi-rigid ducting which is a lower figure I reached from searching the internet. The MVHR unit will be centrally located and all ducting can be installed with minimum bend and distance. Is this reasonable or does it make my whole attempt nonsensical?

How do I build an internal step, up 120mm to a door, over a screed floor with UFH? Both the floor and step will be tiled. I imagine a form with a concrete mix. Or do I need a specialist compound (eg Bal Level Fast)? I am not at all concerned about a fast dry but do I need something because of UFH? Thanks

Is this enough depth of 804 stone for this cottage floor? -50mm small/medium stone -30mm compacted 804 stone -DPM -100mm insulation -DPM -UFH in 70mm screed I was expecting way more depth of 804 stone but the builders have put in just approx 30mm (once compacted). How much depth is needed?

Hello We have a small cottage in Ireland with exterior walls of old stone and 100mm EWI. This is the plan: 100mm EWI (exists) 400mm old stone wall (exists) Breathable airtight membrane against wall 20mm air gap Thermally bridged metal stud frame (with insulation) Plasterboard Does that look like a good plan? Do we need a vapour barrier? The old stone wall is sometimes exposed repointed stone, othertimes several renders. It is extremely uneven. How do we secure the stud tracks to a wall that is all over the place? Any ideas for this appreciated. I imagine an adjustable bracket hopefully providing a thermal bridge but cannot find anything. Many thanks, Phil

OK. Sorry for the delayed response, and thanks very much for the pretty unanimous and clear need to go deeper. Looks like we can get down to 180mm, will try to go deeper but wont know til on site. Will do the 2 staggered layers, foam, tape and polythene. Will look into the price for a top layer of phenolic. Thanks everyone!

We are rebuilding an old cottage and have only 120-130mm available for insulation underneath the UFH (probably in 55-65mm of liquid screed). What type of insulation, what suitable product, will give the most insulation? Thanks!