DavidHughes

TerryE, Quite the contrary, if I wished to ignore people I would not still be here. Please make your case and provide numbers to back up your summary. No one else has. This is my point. If you say it, please prove it with measurements and/or calculations. Anything else is just an opinion and with thousands of pounds at stake for the homeowner I think future non contributing readers will be very interested in the numbers.

>onoff >All the facts, figures, calcs and arguments against MVHR are pretty irrelevant tbh in the face of the sheer numbers on here who have it I am not quoting you out of context. I am quoting you very clearly in context. If you think that my comment on the number of counter posts with no substantiation is in anyway unfair then I wholly disagree and ask you to provide facts rather than conjecture. This is a discussion about whether mvhr is worth the price. If you or any other contributors disagree with my assessment then please post with facts. The air quality issues have already been dealt with and so have the damp issues. For reference my view is that if there is a damp problem then it is probably best to address that first before considering an mvhr system.

>Good draft sealing doesn't come even vaguely close to the sort of measures needed to get down to the sort of airtightness where MVHR starts to save worthwhile amounts of heat. Jeremy, please explain. a) why? b) even if you are correct, which I dont think you are, my heat loss calculations (which agree with yours) based on 100% sealed still present a conclusion that shows low benefit in terms of energy saved per year vs large initial outlay. I thought that this had already been tacitly agreed because nobody has come up with a counter argument. The house sealing issue has been gone over on many previous posts and just doesn't stand up to scrutiny in terms 9h heat lose.

>onoff >All the facts, figures, calcs and arguments against MVHR are pretty irrelevant tbh in the face of the sheer numbers on here who have it, like it and see the benefits. Since when did the number of posts otherwise make my case incorrect?. And please explain why it is irrelevant. This is serious. Nobody has presented counter calculations or measurements and no one has challenged my postings regarding energy efficiency with evidence to support their counter claims. If you wish to post then please inform with facts.

>Mike Please read the full thread but if you want to save time and possibly money read page 6 from about half way down. Then look at the excel calc on page 6 plus my opening comments at the start of page 1.

>The regs do not refer to ACH, as it's not the way either air permeability or ventilation is measured in Part F. Part F references everything to areas, not volume. yes of course, that's exactly what I was saying to Peter and also it does not change my case as previously posted.

And peter, you have still not responded to my 0.3 ACH x house floor area question. Please do

And PeterW you don't know the regs. The 0.3 ACH is a continuous running regulation, not a boost requirement as you have stated. The boost requirement is usually higher but dependent on house layout depending on number of wet rooms and kitchen extractor. Please be accurate! For everyone else just read section F of building regs, available via google in seconds.

>Prodave My mvhr system is in and running for 6 months now with calculations to match. Please read my posts and respond with facts. I have answered all of your questions in a previous post, item by item, and you have not addressed any of them. >PeterW Then please quote and reference your facts. And please dont quote passivhaus standards without context. This is not a passivhaus conversation and even if it was the ventilation aspects which we are discussing are completely independent of passivhaus standards. A passivhaus is still subject to the same ventilation energy calculations as any other house with good draft sealing. Please give me facts relating to energy savings with an mvhr,. David %

>PeterW Even if you were right, which I don't think you are, please quote the section F regulation which contradicts my assertion. Even if you are right, which remains to be seen, it still does not in any material way change my evaluation. If you think that I am wrong please Correct me with facts.

>PeterW That is not what the regs say. As I have previously explained . Read the Regs!

>Oz07 I think that you will be very pleased with the air quality results. You need good glazing but only sensible levels of house draft sealing to capitalise on this. Chase those pesky plumbing holes behind sinks into stud wall with a vent straight up the wall and outside! But there is no need to go mad with it unless you are chasing Passivhaus accreditation. The only issue I have with all of this is value. OK not Quite. If you were to press me I could argue about embodied energy in manufacturing and the lifetime of the hardware involved vs energy saved/year. You will not be saving yourself any money and you will probably not be saving the world through CO2 emissions (running costs plus hardware manufacturing costs., plus filters). I think this is a luxury product, nothing more. You all have no idea how hard that was for me to say after years of chasing this particular rabbit. David

>coconutsaregood The air flow rates are set out in Building regulations Section F available online with a simple search. To enable you to cut to the chase without reading and understanding 20 pages it requires an overall house ventilation rate of 0.3 x the area in square meters of your house in Litres/s. So 100m^2 house requires 30 L/s to comply with regs. There is no consideration of ceiling height or house volume the regulations probably assume around a 2.4m ceiling height in every room. There are specific requirements for extractor fans in bathrooms and kitchens to clear vapour on a maximum boost rate but unless you have an unusual house arrangement the two rules are largely the same give or take a few L/s. If you want your house to be sellable then you must comply with this AND engage Building Regulations at the Council. If you don't need to do this then just DIY anything you like and live with it. In my last house I found 0.05-0.1 ACH perfectly acceptable but back then I wasn't subject to building regulations. The DIY option works well as I did 20 years ago, but now the authorities want it tested and inspected. David

>Joe90 Frankly @DavidHughes if you don’t want MVHR then don’t have it. I do installed, tested and measured, hence my posts. Please read before responding. >Joe90 mine cost relatively little to install, unit from Ebay, self made manifold, terminals, silencer. DIY install so the costs were minimal. Please state your hardware costs and time to install, test and commission. That is the point of this thread. > Regarding benefits my air quality is very good and consistent ... We've already gone over that.

>MJNewton I agree with your comments on air quality but your comments on cost do not stack up. Please don’t conflate the two issues. What I don’t agree with is that you say “£13.50/year sounds pretty amazing value to me!” The true cost is £13.50/day plus say (£2000 DIY + £5000 Installed) / 2, so £3500 amortised over 30 years (which is generous) = 32p/day plus running costs of 4p/day plus filter costs. It is really costing, for even a small system 35-40p/day. >Declan52 “So not even 4p a day” See my comments to MJNetwon >Jeremy Harris >Frankly I'd pay a lot of money to run the thing just to get the air quality benefit. You are a) paying a lot of money and b) getting an air quality benefit. My comments are so that everyone understands what they are getting for their money. Also, your spreadsheet and graphs are very good and I think accurate but nowhere do you evaluate the cost. This is my only issue. >Joe90 >Just had a shower, MVHR came on boost automatically to reduce RH and it will go off automatically when it gets back to normal. No trickle vents to create cold draughts, what’s not to like. All good, but what you say has nothing to do with cost/benefit, and this is the central theme of my post. One could say “I really like my house because it has a huge central heating system for winter and a magnificent aircon system for summer” >ProDave >I would be REALLY surprised if your real-world energy saving is only £81 per year with the mvhr. Those are the numbers which I have calculated and I have more than 10 years of experience running these system, that’s the simple house heat numbers, I invite you to prove me wrong with data rather than conjecture. >Are you taking account of the fact that if you don't fit mvhr you will have to fit trickle vents in EVERY window. You will have to fit an extract fan in the kitchen, utility and every bathroom. Unless you spend a lot of money on those fans, they will be leaking air all the time even when not on. Most windows which require them (like bedrooms) already have them. Fitting extra trickle vents in walls is very simple and not expensive compared to an MVHR. Most bathrooms already have extractor fans, which cost £30-50 for a good one and already have flap valves when they are off but are still a bit leaky but are not that bad. Could be improved. For the two years before I fitted this system, I had largely given up on turning the shower extractor on because there was no damp problem and the ensuite cleared within about 15 min due to the slightly leaky flap valve on the old extractor. >So, with all the ventilation you will NEED I suspect your ACH will be a lot more than 0.3 just by fitting all the ventilation that building regs require. I have measured my needs based on damp control (not an issue at all in my house) and CO2 monitoring. Both are comfortably satisfied by 0.1 ACH, in fact over the last few months I have dropped it to 0.075 based on C02 monitoring. If there were a few more people I would up it to maybe 0.15 ACH, or, as I do press button 2 on the controller for 0.3 ACH with cooking and guests. My master bedroom reads 750ppm CO2 in the morning against a background of 400 ppm and a house average of 550 ppm when occupied by two people indoors all day. And for example, a school maximum recommended is 1500 ppm. Again, I ask you to present facts rather than conjecture. >Sealing the house up and not fitting mvhr is not an option unless you make other ventilation provision. That’s obvious, my house is, what’s your point? >But do carry on and when it's finished let us know your real-life energy bills once you have made all those holes in your house. And let us know if you get any condensation or lingering smells anywhere. I have been running this house on MVHR for 6 months over a stormy wet winter. I have had no problems. I have now ‘let you know’ - Please comment. >For me, mvhr is worth it, not to have anti back draught flaps clattering in the wind, not to have internal doors blow shut when you open an exterior door etc (with a sealed house with mvhr you can open 1 door or 1 window even on a windy day and not have any through draught) These are trivial/non problems. If your flaps are banging then put a put a bit of rubber trim on them. I had the same problem on my last house in an elevated position in the Mendips and the rubber trim sorted it. Even then it needed very high winds to cause the problem. Are you seriously suggesting that one spends thousands of pounds to not have an open-door slam in high winds or flaps clatter? >Simply Simpson >what are they? does a trickle vent move the air where it is required to avoid the build-up of condensation and therefore mould growth? mvhr supply is in the opposite corner to the extract and will move more air from across the room. They are vents in the walls or the windows, commonly built into double glazing units for many years now. If you wish to use them instead of MVHR then you need to place another vent on the other side of the room or in an adjacent room through the ceiling. Thermo-syphoning (hot air rises) will do the rest. You don’t need that much flow, see previous comments. If you do need to control damp, maybe you should look at the damp problem first, MVHR is expensive. <Jeremy I think you are clutching at straws here, however… <Trickle vents have a very highly variable flow rate, from near zero on a still day (so almost no ventilation) to a very high flow rate when extraction fans are running. Then just open the windows in summer, that’s what everyone else does! >Noise was one of the main problems we had. In two of the three houses we've lived in with trickle vents they howled like a banshee with the wind in a particular direction. Get better vents. Also are you seriously saying that in high winds you can’t hear wind noise from anywhere else in the house? I don’t think so. >Dirt was another issue; they produce dirty smears where dirt and cobwebs get pulled in around them. That’s valid but dirt accumulates all over the house from all sorts of sources, the house always needs cleaning. An MVHR will not stop the general cleaning requirements on a house. David Hughes

I have run my system and reviewed the numbers. My heat flow numbers come out the same as Jeremy's spreadsheet, in fact we have very similar houses. I've worked out the cost/benefit of my MVHR and it's not pretty. See calculations below. The numbers show savings at 0.3 ACH which are bad enough but in reality 0.1 is more than adequate most of the time. These systems will never pay back. My numbers assume a 100% air tight house so the numbers below are a best case scenario. My house isn't 100% but its pretty close. No amount of air tightness improvements will improve the underlying issue. I stand by my first post. Unless you have an air filtering requirement or a damp problem (in which case it would really be better to fix the damp) then don't bother with MVHR, just go with well designed trickle vents and maybe some strong extractors with valves for occasional use.

>Again the figure used is in the spreadsheet, 1210 J.m³.K Finally found it amongst the posts. Thanks. That, the 0.43 ACH and and the 85% efficiency figure has gobbled up most of the discrepancy.

Hi Onoff, > Have an air tightness test done How much does this cost for a 100 m^2 bungalow? David

Hi Jeremy, I'm looking at your graphs now and can't quite make my calculations match yours though I am in the same ball park. Please can you confirm your mean annual continuous flow rate, mean annual outside temperature and mean house temperature. It looks like your MVHR is delivering about 90% efficiency, can you confirm? You might add the density and SHC of the air which you are assuming and your cost/kW.hr for re-heating air lost with no MVHR. This will help me align my calculations. David

My house is much better than yours was to start with but it was still a challenge. I think I spent about 6-8 hours sealing spot light fittings alone.

>Interesting post. Tell us how you went about achieving an airtight design.. Start with a relatively modern single storey solid floor house with few leaks to start with then... With great difficulty, persistence, pressure sensors, flow meters, aluminium tape, silicone, insulating foam, some new windows, new door seals, smoke.... Took two days. Although I'm not attempting passivhaus standards I might just get someone in to do the pressure hold test if it's not too expensive. .

Thanks for pitching in Jeremy. It was your posts which I found most useful during planning and installation. I'll digest your numbers over Christmas. I too have my house fitted with albeit simpler measuring gear. My house is very well draft proofed, insulated and glazed. I'm currently getting 90% efficiency +/-5% on air heat recovery but will be fitting some more accurate and more sensors from old work kit to take a closer look. I'm still struggling to see how I'm making more than about £100/year at the most optimistic estimate in energy savings. Might be a house size/type thing. David.

Well, having found this forum a few months ago and benefited greatly from the well-informed posts concerning MVHR I felt I'd like to share my own experiences and give a condensed list of useful practical tips. Unfortunately on reflection I feel compelled to write a different kind of post but still in the spirit of helpful advice. Having just DIY installed a professionally designed and supplied MVHR system in my bungalow, and looking closely at all the time and numbers I conclude that it is largely not worth it in terms of either cost or performance. I have come to the conclusion that a carefully designed system of adjustable wall, window and ceiling vents will fulfil the same needs at a fraction of the price and effort. The primary reason for this conclusion is that building regulations section F requires a continuous ventilation flow rate for an MVHR system of 0.3x the floor area in L/s. For a 100m^2 bungalow = 30 L/s. At this ventilation rate, assuming an average 21C inside and annual average 10C outside, with gas central heating, you will be saving about £200/year on heating with a 90% efficient MVHR. My experience with both this house and a previous one with an MVHR system is that you actually need only a small fraction of 0.3 ACH for any house to ventilate it adequately. Previous other posts on this forum also conclude that the required flow rate which they actually run their houses on is much lower than 0.3 ACH. The 0.3 ACH value is an outlier worst case, most owners of modern houses will find 0.1 ACH completely comfortable, even with cooker hoods and showers taken into consideration. I have personally found that about 0.05 ACH continuous is absolutely fine for a few people in a small house. If you now look at 0.05-0.1 ACH continuous you find that the heat saving per year is £30-£60/year. Out of interest I also do scuba diving occasionally and can confirm that about 0.5 L/s for one person doing moderate exercise adjusted from 10-20m pressure to 1 bar at the surface is normal. Now lets look at cost and effort. For my 100m^2 bungalow I paid BPC ventilation (who, despite what I have said are excellent in every way) about £2000 to design and supply an MVHR system for my 100 m^2 bungalow. I have very conservatively spent 100 hours planning, installing and testing the system. I have had to take paid time off work to allow building control in to inspect. I have had to hire a calibrated flow meter at a cost of about £140 including postage. I have messed about with it for many hours (about 20) to balance the system. I have spent at least 10 hours preparing the relevant documentation for Building Control. I have had to shave the bottom off all of my doors to make a 10mm gap for through house air flow and in some cases re-paint, I don't even want to think about those hours! I could go on but shall we call it £5000 if I paid someone to do all this? That's not unreasonable. So I pay £2000 and do it DIY for a £50/year payback = 40 years Or I pay someone £5000 for a £50/year payback = 100 years The MVHR unit will probably last no more than 25 years but the ducting will hopefully last a lot longer. According to the manufacturers of the MVHR I need to inspect the filters every 3 months and replace them at 2x£20 every 6-12 months. And if you are CO2 conscious lets not forget the cost of manufacturing the kit in the first place - who knows? So why did I do it? Well I got suckered into it. The last house in which I DIY installed a system like this I swapped an old heat exchanger for a crate of beer, put simple ducting and fans in about 20 years ago. I didn't need to consult building control, just did it and ran it for 10 years. It worked really well and cost me about £400 in bits and about 50 hours time. I started this new house recently and suddenly building control and the 0.3 ACH rule comes in. Still determined I pressed on to make sure my house was compliant but I should really have stopped and thought about it before I spent my £2000 on kit and began work. Are there any benefits to MVHR? Not many. I'm confident that in new build in 20 years time it will all be gone and that carefully planned vents incorporated into high quality glazing units and ceilings will be the order of the day. The only things which I can think of are filtration of pollen and pollution and maybe noise reduction (vents let in noise). If I were to do it again? No MVHR. High quality adjustable wall vents low down in the corners of all bedrooms (the rooms which you want to be coolest). Similar ceiling vents in living areas to let the air out. Bathrooms with good, possibly motorised, flap valves on the extractors. A recirculating cooker hood fan or total extract with similar good flap valve. Chase and fix drafts religiously including floors with insulating and low air permeability underlay. Hire a cone flow meter to see what's really happening. https://www.bsria.com/uk provide this service for £80-140 depending on whether you collect or have it delivered. Set the system at about 0.05-0.1 ACH On a two storey house a duct and low power fan to circulate the air top to bottom (my last house had this and it was excellent) If the layout of the house were amenable ( I have solid floors so no chance) I would probably attempt to draw air in over the foundations of the house to either pick up heat in winter or let go of heat in the summer. Follow the building regs guidelines section F which do have some good rules but don't bother telling them unless you absolutely feel the need to - it's just some wall vents in a house... Regards, David Hughes Ex F35 Lift System Stress, Thermal and Dynamics Engineer and home energy efficiency enthusiast. The Wirral.