MvHr in cottage refurbishment

[Cpd]

 

Ok so please lets just take this one step at a time, i am here to listen and learn and hopefully make the right decisions when the time comes. (Unless i have already made the wrong ones....) I have two houses both are 1.5 storey and both right next to each other. The house i live in is very basic, very traditional and in need of a lot of maintenance and improvements over a long period of time. However having very small children and a partner pretty much prevents any type of serious work being undertaken. 

 

Winters are the hardest as it has very little insulation and obviously costs a small fortune keep it warm. I am not complaining, i could not be more happy with where i am its just a fact.

 

The cottage has a much better roof and will be suitably airtight by the time i finish redoing the insulation. 

 

I would like to get the cottage to a point where as a family we can live in it during the winter and i can work on the main house without impact on the rest of the family. In the past the cottage has been used by our friends and helpers / volunteers but when its up and running i would like to rent it out as a holiday let during the summer to create some extra funds to help pay for the main house improvements. 

 

I aim to install a mvhr unit for whole house ventilation 

 

I have read previous post time and again and i hope i have a much better understanding about mvhr than when it first became an idea for me a few years back. 

 

The cottage is small and the system i hope to design is hopefully going to reflect that. I have a long stay volunteer who is very smart and though not that familiar with mvhr is willing to help me with design as he is smart and can use sketch up. I am very practical and adaptable but i would not call myself smart and i cannot use sketch up. 

 

Hopefully with the collectives help, Mr smarts and my practicality we can design a system that i can install and will work as hoped. 

 

Being a small house the only place for the unit is in the stairwell. There is plenty of height so it does not impose on users and with some quirky wood work i can make it look right at home. 

 

I will gather all the information i need together in a presentable form and will then start asking questions. I already have an mvhr unit as it was super cheep on ebay.  Its oversized but can be adjusted according to requirements.  

 

Just a few of Mr Smarts screen shots from Sketchup. As i said i will get all the info together and come back to ask questions. Please be patient with me on this one. 

 

 

 

 

 

[SteamyTea]

It may well be worth you getting an air leakage test done, that way you know where you are starting from.

You could make your own fan and manometer/pressure gauge if you are fairly practical and save yourself a few quid.

[Nickfromwales]

1 hour ago, SteamyTea said:

It may well be worth you getting an air leakage test done, that way you know where you are starting from.

You could make your own fan and manometer/pressure gauge if you are fairly practical and save yourself a few quid.

Combined with a smoke machine will soon identify where the bad air leaks are so they can be plugged. 

[SteamyTea]

I am happy to be the smoke machine, will work for Marlboro

[Cpd]

Ok i have the means and ability to make a fan and smoke would give a clear indication of air leakage, i first need to finish rebuilding the front and back doors block up the unused chimney and complete the insulation upgrade. I am trying to make sure that i have all my duct runs confirmed before i inadvertently block off potential pathways, i need to get the upstairs bedrooms back to habitable so that the volunteers can come back in from outside....... its not that bad but i would like to have sleeping space for them again this summer. The rest of the refurb will be going around them. Thats why i need to make some assumptions on air tightness at this time and make sure i have the hardware installed but not commisioned. 

[ProDave]

The big mistake just about everyone makes with old Scottish croft houses, is to make a "plasterboard tent" inside them.

 

I can almost guarantee that when I remove a switch or socket from the wall a howling gale will emerge from the hole.  In almost every case, the framing and plasterboarding that lines the walls is open up into the loft space from where cold air can get between the wall and the plasterboard. 

 

Add to that, most have no insulation at all in the room in roof ceilings, no wonder they are cold.

[Cpd]

@ProDave i am very aware of what you are saying and the cottage though a very traditional croft house is not going to be a plasterboard tent. I am in total controle and have a full understanding of the importance to detailing in many aspects of the refurbishment and try to educate myself before making mistakes. Eventually this will be a fantasric little summer holiday cottage but have the ability to house me and my family over the winters  when i will have a chance to start addressing the wooden panelled tent we live in at the moment. 

The aim of this thread is to share my ideas, bat them about and come to a conclusion. With all you great people out there i am sure i can come up with something that may not be perfect in everyones eyes but will be the best of what i can do with the materials i have or can afford to get. 

[Crofter]

@Cpd What MVHR unit are you looking at?

[Cpd]

@Crofter    I got this one for £300 new of eBay it can do up to 370m3 and my place is shy of 250m3 so i assumed.... this would be a bit big but it has the ability to be wound right back so hopefully... providing minimal work and good efficiency but have the ability to boost from kitchen and bathroom on a humidistat or switch..... it was my first “risky” buy of ebay and i am yet to understand the consequence of that decision......  

[ProDave]

@Cpd I wasn't trying to imply you were going to do a poor job, just mentioning that the vast majority of builders do.  One in particular I rewired a few years back,  builder doing the refurb "insulated" it by including 25mm thick kingspan behind the pasterboard (still the usual plasterboard tent behind that kingspan)  He genuinely thought he was doing a good job. He even told me that when he did his own house, he went overboard and fitted 50mm thick kingspan to insulate his plasterboard tent.

 

It will be interesting to see how you make a proper job of doing it.

[Crofter]

That unit looks decent, nice find

[Cpd]

@JSHarris thanks for the spread sheet. It will be very useful  to help me understand and clarify information for both my thread on the AsHp and this thread on MvHr My first question is about efficiency of the Mvhr unit do i enter the efficentcy as stated on the machine or does one down grade the manufactures figures to “real life” expectations ? 

[Jeremy Harris]

Best to use the efficiency that's given in the SAP database for the MVHR unit, that should be pretty close to reality.

[Cpd]

Am getting close to needing to instal my mvhr and ducting but want to get closer to choosing the ducting. Its a small cottage and there is only 51m of supply ducting needed and 31m of extract ducting required. 

 

12 hours ago, Stones said:

I've had MVHR in 4 houses now, but this is the first I've had to fit a silencer. Not sure if its the MVHR or type of ducting I used this time (semi rigid) around.

  

Given the small amount of pipework needed i want to get the best i can. Semi ridgid is appealing (and seems to be the preferred option on here) for its simplicity but as my duct runs are relatively simple and short  should i be looking at rigid. Noise reduction is very important to me as its a small house and short duct runs from unit to extract / feeds.

 

lounge feed 16m

end bedroom 11m

middle bedroom 8m 

 

bathroom extract 10m

kitchen extract 5m 

stairwell extract 2m 

 

Fitting silencers / attenuators will be required but a bespoke approach is needed as space is tight, following @JSHarris and @Stones approach on how to do this.

 

so my question is what recomendtions do people have for quality ductwork, i will look at fittings next but before trying to get a package deal i want to get some independent advice from people who have fitted and are living with mvhr.

 

As always thanks for any advice. 

 

 

 

 

 

[Jeremy Harris]

From what I've seen, pretty much all the 75mm/68mm duct is identical.  From what I can gather the design has been licensed to several different manufacturers, who now all produce their own version of it, from Polypipe (Domus), though to HB+, and several others.  The main difference between the various suppliers is in the design of the plenum chambers and terminals, and the method they have chosen to regulate flow rates.

 

I used the HB+ system, and that uses open room terminals and restrictor rings fitted inside the plenum chamber to adjust flow.  It's fiddly to set up, but has the advantage that the flow restriction (which can create flow noise) is inside the plenum, which tends to make the terminals a little bit quieter, I believe.  Other manufacturers use a simpler plenum chamber without the ability to fit restrictor rings and use adjustable room terminals.  There's the potential for these to very slightly increase the noise level on boost, plus they could have their adjustments accidentally changed when cleaning them, but frankly I don't think it makes a great deal of difference.

 

I found that silencers fitted close to the MVHR unit made a very big difference, and completely removed all noise when the system is running normally.  There is still some very slight noise when the system is on maximum boost, but even that is far from intrusive and only really barely audible in the kitchen and bathrooms, it's a lot quieter than a conventional kitchen  or bathroom extractor fan.

 

[Stones]

I don't think there is a right or wrong answer.  All our previous installations used a main duct with branches off to individual rooms.  Ducting was a mixture of plastic and flexible.  I know many will be some sharp intakes of breath that I used flexible duct, but you know what, it worked.

 

The smaller bore semi rigid stuff I used in the current house was a lot easier to install, but I do think its the reason I've needed to install a (large homemade) silencer.

 

My neighbour has just installed a system using main duct runs of polystyrene duct with branches off, a silencer at every room outlet / inlet.  It's yet to be commissioned but it will be interesting to see how that performs noise wise.

 

 

[PeterW]

I’m doing a “hybrid” install as like @joe90 I picked up a decent Mitsubishi/Kingspan unit for less than £60 in an auction and it was brand new. 

 

So far I have the terminals and the ducts in back to the location the unit will be placed - I will most likely build a silencer as part of the distribution system. 

 

 

I used a spreadsheet to work out the duct velocities and found that I could drop to 55/63 standard electrical duct for the distribution with no real issues.

 

Terminal plenum are made of off the shelf uPVC solvent weld fittings and the terminals themselves are from Toolstation ..!

 

 

Very nice white steel two part terminal with a galvanised steel flange that has been glued / plastered into the wall or ceiling as they fit with about 2mm tolerance into a piece of soil pipe. You can just see this one in the top corner. 

 

 

They have a foam gasket on the outer part and are a 1/6th turn to fit them - you can see the coarse thread in the image on the website. There are no sharp edges to the valve itself and they seem well made. 

 

 

There are two where we have them wall mounted, the remainder are ceiling mounted. I may also fit carbon foam filters into the extracts in the kitchen - there are two - so that it keeps grease out of the ducts. 

 

Total spend so far is £150 on ducts, £150 on 12 terminals and parts (that’s a solvent cap, solvent stub branch, bracket and offcuts of pipe) £60 on the unit and the most expensive was £80 on the proper Mitsubishi controller ..! Another £100 should see me done including filters and externals. 

[Stones]

How many metres of duct have you used?

 

How have you secured / fitted the ducts to room terminal plenums?

 

The steel room terminals are nice.  I used them in all of our previous builds and they are a lot less intrusive / better looking than the plastic ones I currently have.  I've still got one spare somewhere, will have to dig it out and see how good a fit it would be with our terminal plenums.

[Jeremy Harris]

@PeterW, I really admire your ingenuity!  I wish I'd thought of doing something similar, as using standard plumbing fittings allows a heck of a lot more freedom when trying to fit things in.

[Cpd]

@PeterW wow this is a really good idea and something i will follow up asap, thanks for your input. 

 

[PeterW]

2 minutes ago, Stones said:

How many metres of duct have you used?

 

135m of duct as the original plan was to have the unit above the bathroom ceiling but tbh it just didn’t fit properly and would have been a bugger to replace. As everything has moved it’s added 40m of duct in total. 

 

Longest run is 23m which is the full length of both legs of the “L” shape of the house. 

 

15 minutes ago, JSHarris said:

@PeterW, I really admire your ingenuity!  I wish I'd thought of doing something similar, as using standard plumbing fittings allows a heck of a lot more freedom when trying to fit things in.

 

Thanks Jeremy !! It came about from a partial cost and partial “it can’t be that hard” sort of discussion ..! It was by chance we found that the electric duct is a tight interference fit into a solvent boss - we tried a couple of things including rainwater fittings but they soon added up ..! The duct tape is just there to ensure nothing comes loose in the future although given how hard it was to get it to fit, I don’t think it’s coming out any time soon ..!!

 

The most expensive part believe it or not was the solvent end caps - in all the downstairs rooms these are “bonded” onto the floor above with a decent high strength adhesive and then the bracket just keeps the lower pipe in place. 

 

The nice thing about the Toolstation vents is the two piece design means the soil pipe can be slightly above the plasterboard ceiling and then a hole is cut and the flange covers the small gap between the bottom of the pipe and the ceiling itself so no difficult cutting needed to get them flush. It will also give a lip for a drum of carbon foam to sit on in the kitchen. 

[Stones]

Roughly speaking then your duct was about 1/3 the cost of the slightly larger bore stuff many of have used.  Well done!  From what you say similar 1/3 - 1/2 the cost for the other comparable parts? 

[PeterW]

33 minutes ago, Stones said:

How have you secured / fitted the ducts to room terminal plenums?

 

So the room terminals are made from a solvent end cap, and a solvent boss fitting with a variable length of solvent weld pipe to make up the depth needed. Some need about 150mm to fit between the ceiling and the floor above, others are just about 90mm as they are only secured to the ceiling joists. 

 

You can see the boss here - the middle branch is pre-drilled and I did consider using strap bosses but the caps would have then not fitted. 

 

 

The flanges do rattle a little in the 110mm soil however a liberal use of solvent free adhesive means that they are then held into the board and the plenum. The plasterer then skims over the flange and they are going nowhere ..! Flanges are about 0.8mm steel and well made. 

 

I looked at duct costs and from memory I think it’s come to about the same as a single roll of standard duct from any of the usual suspects. 

 

Prior to finishing I’ll be pulling a pompom sprayed liberally with Mr Sheen (other sprays are available) through each duct to clean out any dust. 

 

 

[PeterW]

10 minutes ago, Stones said:

Roughly speaking then your duct was about 1/3 the cost of the slightly larger bore stuff many of have used.  Well done!  From what you say similar 1/3 - 1/2 the cost for the other comparable parts? 

 

Cost-wise I would say yes.

 

A plenum is £7.85 plus a pipe offcut, and the vent itself is £6.98. I also made sure these all got bought with “offers” so total is around £12.50 per room. 

[Stones]

33 minutes ago, joe90 said:

I wish I had known about the cheaper duct. Here are my homemade terminals held together with expanding foam and grab adhesive, also my MVHR unit slung from the roof on rubber mounts, not sat on the loft floor so no change of noise into the house, also ( on top) my homemade manifold made from ply and lined with acoustic foam. The one thing I am yet to do is attach any restrictors on the individual pipes  leaving the manifold to balance the system.

 

Sorry @joe90, somehow managed to delete your post when trying to quote it.