MVHR DIY install in Loft conversion

[Rama k p veerapaneni]

Hi All,

I live in 1950’s First floor Maisonette with Loft conversion which started 4weeks ago. I have previously not known about MVHR system and didn’t take into account in designs however due to lot of condensation in current floor bathroom and kitchen and lot of heat loss, i thought to add MVHR in my Loft in a corner.

I have contacted BPC and received Full Ventilation guide with design attached here. I want to install it myself or with current builders and want to make sure the installation is done correctly. I have spoken with builder's who said they have not installed one before but if ‘can do it’ is the reply i got. I have seen great advice in this forum and i am looking for any posts with links that previously had been discussed which has step by step installation guide?

Also, as i have not thought about this MVHR installation previously, do i need to need to cut through joists for 75mm radial ducting to go though? and will this compromise any structural integrity of loft floor? I am also attaching list of materials supplied by BPC which should be receiving next week.

Please let me know if any materials i need which are not in this list ex: how to add or which humidity sensors to MVHR system.

Your advice will be greatly appreciated. Many Thanks in advance.

 

[Rama k p veerapaneni]

Hi All,

Any advice is greatly appreciated for step by step installation by myself for MVHR in my Loft which is in build stage as i have few more questions from my original post. I have had all materials delivered today and hoping to do the installation with my friend who is helping me over coming weekend. Sorry for long post.

I have installation guide from BPC website but want to make sure i cover all aspects of installation except electrical work and connecting condensation drain to another drain pipe. In full design i provided in my 1st post, we will have a small bathroom next to cupboard where MVHR is going to be located. Is it ok to connect condensation drain pipe to waste pipe in loft bathroom?

I spoke to builder and quoted i was £3000 for installation without materials. However, i may need builder to connect drain pipe to loft bathroom waste pipe.

Do i need to complete electrical connections for any controls before MVHR unit installation? as i thought i read somewhere this is the process. I have no idea about electrical stuff. Also, am i correct in saying all ducts need to be covered until MVHR is switched on after loft and current floor renovation to avoid dust getting into unit?

Finally, my property is going to be around 95 m2 once Loft is complete. Please, can someone provide me calculations for how much extract and supply ventilation levels in l/s which meets BC regulations (should the levels be a bit more than minimum BC regulations in Approved document F?) and have around 50-55% efficient (is this number correct?) operating capacity for MVHR unit and to come on Boost mode if there is too much humidity in kitchen/shower area? BPC has mentioned in my contact with them in last 2 weeks as 22l/s. I will follow up with them this week if this is for one particular room or for whole house. How do i calculate how
many ACH for a family of 4 with 2 young kids in a 95m2 first floor maisonette?

Also, it is greatly appreciated if my OP questions can be addressed?

Sorry for long post and Many Thanks in advance

 

[SimonH2]

Also, as i have not thought about this MVHR installation previously, do i need to need to cut through joists for 75mm radial ducting to go though? and will this compromise any structural integrity of loft floor?

As I view the diagrams, no you do not need to cut any joists. In fact, you MUST not go cutting 125mm holes as you'd destroy the strength of the joists. Also, you'd not be able to thread a rigid pipe through.
Taking another look at the materials list, it looks like most of the ducting is 75mm flexible. But you'd still need 100mm (4") holes and you could not cut those without seriously weakening the joists.

Ducts that cross joists are above them - in what remains of the roof space. They only run along between the joists the other way.
Look carefully and some ducts run through the roof space one way, down between the joists to run the other way, then up again to reach where the terminals are placed. That's a lot of ducting ! I see 3x 59m on the list !

Other than fitting the roof terminal, that's all DIY. During works, you should avoid getting rubbish into the ducting. Fine dust will blow through and get caught in the filters, heavier stuff could could sit in the duct - obstructing airflow and possibly rattling annoyingly.

Yes, you should have it all wired up before applying power.

 

[robinbanks]

75mm flexi duct will fit through an 80mm hole, but the question of whether it would appreciably weaken the joist massively depends on the size of the joist. How deep are your joists? What kind of joists do you have? Solid or engineered?
How high are your ceilings?

BPC will probably send a full install guide that you should read closely. If they don't, call up and ask for one to be sent. I left a builder to install the MVHR in my own house and they couldn't read, so they missed vital things such as putting rubber seals on the ends of the ducts before installing the duct in the plenum. Thankfully, I checked and took them off the job early on, but if you're planning to leave someone to it who's never done it before, I'd keep a close eye on them (you'll read the guide. They probably won't).

3000 quid is a lot of money to install an MVHR in a flat; from direct experience running flexi ducts and connecting them up, even if there is a large amount of joist drilling required, should only take a couple of days for 95sqm, and I'd say anyone who knows how to connect the hose to a vacuum cleaner, and how to use a cordless drill, can perform the install. It's not a complex task

Wiring? If you can plug a vacuum cleaner in, you can connect an MVHR to power. If you're siting the unit somewhere where there is no power, spurring off a socket to bring power to the unit is something you're allowed to do if competent, without oversight/sign off, so just make sure you're competent; it's your family's safety. If you're not competent, a sparky won't charge much for a spur

Yes you can connect the condensate drain to a soil pipe but you should install a trap to prevent sewer smells entering the unit. Do not connect the drain directly to the sewer.

Yes you should block the ducts from getting dust in until you're ready to commission

You can buy an MVHR unit with a humidistat built in so it self boosts when it detects excess moisture

Don't worry too much about the regs; balance it, turn the unit up to the gale force setting the regs require then turn it down to something sensible when the inspector has gone. You'll get to know, if the unit is too high the house air will feel dry. I run mine at 20% at night and 30% in the day, regs demanded 60% which was noisy, uncomfortable, needlessly costlier - lunacy. You'll get to know what setting is right for you