MVHR Newbie

[Jimbouk]

Newbie post , so I apologise for any blatantly obvious questions in advance, (I have had a look around for answers to no avail)...

 

As mentioned elsewhere I have just purged the footing on our project in Devon, and the scope creep has started...

 

At present had planned on conventional extractor fans, in Kitchen, bathroom and ensuite, this has progressed to should I have a centralised system, which in turn could become a full mhrv system.

 

Now if this was to be my main home, I would jump at Mhrv, however I'm initially only going to be using the house for occasional weekends and holidays, before the haters come out, the family has been linked with the village for 4 generations, and one day in the distant future I might retire....

 

The thought of an Mhrv system whirring away in an empty house does not seem right to me. Also I'm trying to do this on a budget, with a view to enhancing in the future, but conscious that it makes more sense to put ducting in now, even if it is not connected up!

 

I'm looking to get a decent degree of air tightness, it is a timber frame and cedar clad construction. Detail below

The layout, will be primarily glazed to the South West Aspect, with a 2m roof overhang to provide solar shading, however I'm conscious that it is likely to get warm in Summer, so if I had an extract vent at the in the main front room, at the opposite side to the kitchen, would this help to extract hot air from the house? (Summer bypass?)

 

The front aspect will have 3 glazed sliding doors totalling  7m wide 2.4m tall, which will be open as much as the uk climate permits, kind of negates passive haus...

 

Also there will be a log burner in the front room, is this going to complicate the whole mhrv deal?

Thoughts and comments welcomed!

 

 

[Crofter]

Hi and welcome. No such things as stupid questions, except the ones you don't ask

 

Why are you concerned about the MVHR running whilst the house is unoccupied? It should only be costing about £50 a year in electricity and for that you get peace of mind that the house is going to be free of mould and damp. I suppose you could achieve the same thing by having dedicated passive ventilation that you are happy to leave open whilst the house is empty and unheated, but imho achieving that securely is more of a headache than simply using the MVHR itself.

 

My understanding of how MVHR interacts with extractor fans or woodburners is that it's not a big deal. Extractors are not going to be running for very long periods anyway. I have heard of integrating cooker hoods with MVHR but I think that is a recipe for blocked filters. For the woodburner, it's best to get a room sealed one if possible, for all sorts of reasons, so the MVHR won't even know it's there except for the brief moments when the door is open for refuelling.

[ToughButterCup]

Welcome.

 

3 hours ago, Jimbouk said:

Also there will be a log burner in the front room, is this going to complicate the whole mhrv deal?

 

No. Get a sealed log burner. Get someone who really knows how to design it into the house.

I haven't quite finalised the design for mine, but here's too much detail on how I arrived at the design we have - thus far. 

The low occupancy issue is an aspect I haven't had to consider. My first thought was that  you might therefore be tempted to fit trickle vents. Probably not a good idea in terms of air-tightness.

 

Given a SW orientation, you'll need to consider the effect of insolation. You are in Devon.  Thus it might be an idea to run a PHPP model (£200 to get it done for you). Simple answer to insolation and low occupancy: draw the curtains before you leave. Or fit super-expensive treble glazing units with integral self closing blinds (Internorm). The principal advantage of that is you won't advertise your absence.

 

@MrsRA fell in love with individual MVHR units built in to Internorm windows. Shockingly expensive, but in your case you might be able to get away with fitting (say) two of those instead of a bigger system.

 

 

 

[Stones]

Having lived in several houses with MVHR, and currently renting one without, I can say hand on heart that you wouldn't regret the decision to install MVHR.  Setting aside potential energy saving, the biggest benefit and the one I'm interested in is the superior air quality and elimination of internal condensation.  As Crofter says, if nothing else cheap to run and peace of mind when you are not there.

[SteamyTea]

Are you going to heat the house when it is unoccupied?

This could make a difference to your decisions.

If it is left unheated during winter, then there is no need to have the HR part of the MVHR.  During the warmer months, you probably don't want heating anyway, so the HR is not needed.

I may be worth looking at a passive ventilation system, they are pretty basic really, but a pipe and a venturi.

 

Why are you going for a wood burner?  If the house is low energy, you will not need it for heating.  If it is for 'cosiness' maybe think of something else.

[volcane]

On ‎15‎/‎01‎/‎2017 at 15:29, recoveringacademic said:

 

 

Given a SW orientation, you'll need to consider the effect of insolation. You are in Devon.  Thus it might be an idea to run a PHPP model (£200 to get it done for you). Simple answer to insolation and low occupancy: draw the curtains before you leave. .

 

@recoveringacademic

Hi,

Still trying to work through some details before we actually start (things haven't been working so well for a while)

 

I think we need a PHPP model worked out for our house, no certification but I'm worried that it may overheat of that the upstairs bedrooms may be too cold. We have had a quote for the PHPP calculations coming in at over £2k, and I remembered seeing the above and wondered who would provide the above service?

 

thanks

 

[Dudda]

Another thing to consider most MVHR units can be set to an 'away' or 'holiday' mode where it runs at a much lower, efficient and cheaper speed to reduce the £50 to around £30 or even £20 a year. This is still enough to ensure the house is mould free and well ventilated while you're away.

 

Another option. You could also look at just installing the ducts and fitting the unit when you retire? Having the ducts installed is the messy part which can't really be done later. Who knows. You may have money in 3-5 years for a MVHR unit then.

[Jimbouk]

Many thanks for the responses,

 

I recognise now that the running costs will be low and benefit the house both when occupied and left empty. It will be heated via gas fired central heating using an underfloor system, left low in the Winter when not in active use.

 

The log burner will be one with an external air feed.

 

Looking like I will put in all the ducting as we build and see how badly I've over spent by the end, then decide on whether the system goes in now or in the future. I suppose I could install a MEV pump and just connect up the wet rooms initially?

[Crofter]

Just make sure the duct size is compatible with the sort of unit you are likely to install... shouldn't be a big problem though. Bigger ducts tend to be quieter, by the way.