Is a partial MVHR useful?

[Ferdinand]

I need to improve my ventilation, and I am thinking about options.

 

My house is a 2010 extended-upwards-sideways-and-backwards bungalow with three bedrooms and a bathroom in the warm roof - and I only have a limited number of remaining triangular roof spaces to play with.

 

The house is reasonably well insulated, but was not targeted for near passive renovation or similar standards.

 

One driver is checking C02 levels, which in a couple of places go up quite high, and do not come back down again swiftly (==> more ventilation should be considered).

 

I do perhaps have room for the MVHR unit in the garage or planned to be extended utility, but also have limited spaces in which to put the ductwork etc. downstairs.

 

Clearly an MVHR needs balancing etc, but how much benefit will I lose by not installing one in all rooms, if I can get to say 2/3 of the house?

 

Perhaps an alternative is to adapt a strategy of a PIV upstairs, and constant HR low volume ventilation downstairs.

 

I'm going to need to spend some time thinking about this, so I'll welcome any thoughts from anyone who has not quite been able to do a full MVHR, or has installed one in an older house.

 

Cheers

 

Ferdinand

 

[Radian]

Do you have a central hallway that has an open stairway to the first floor rooms?

[SteamyTea]

Are you talking about dMVRH?

 

Why do you think the CO₂ levels are too high, and why are they talking a long time to reduce.

What is the humidity like in the troublesome places?

Have you calibrated the CO₂ meter? Stick it outside and it should read about 420ppm, though you are in a dirty part of the country, so maybe a little higher.

 

[SteamyTea]

And just for a laugh 421ppm here. No dirty Welsh air.

 

 

 

[Ferdinand]

14 hours ago, Radian said:

Do you have a central hallway that has an open stairway to the first floor rooms?

 

Yes - but it's not one with the hall and landing stacked in the same space.

 

Staircase runs off at right angles to the hall.

[Ferdinand]

  

13 hours ago, SteamyTea said:

Why do you think the CO₂ levels are too high, and why are they talking a long time to reduce.

 

Via a not very expensive CO2 meter, which is reporting values up to the 000s in the kitchen.

Reduction is slow ie hours - but quicker when ventilation applied, such as an open window or a cooker hood on max.

 

13 hours ago, SteamyTea said:

What is the humidity like in the troublesome places?

 

Humidity has been normal. I have RH meters in the room as routine.

13 hours ago, SteamyTea said:

Have you calibrated the CO₂ meter? Stick it outside and it should read about 420ppm, though you are in a dirty part of the country, so maybe a little higher.

 

It reads roughly that - 440. Will try it outside.

 

It is one of these, which is cheap so I mogjht be inclined to get a better one before I commit to spending money. However, ventilation is arguably inadequate anyway - there is no kitchen extractor other than the cooker hood:

https://www.amazon.co.uk/gp/product/B09MJ8KPZK

 

F

[SteamyTea]

35 minutes ago, Ferdinand said:

It reads roughly that - 440. Will try it outside.

About right then.

 

[Radian]

2 hours ago, Ferdinand said:

 

Yes - but it's not one with the hall and landing stacked in the same space.

 

Staircase runs off at right angles to the hall.

 

I was just thinking that in a non-airtight building, a single PIV loft type fan introducing filtered, warmed fresh air in a central hallway might be helpful. I know you don't have a loft as such but if one of your eaves spaces has room for the unit and access to the outside air, and the stairway (a lot of if's) then it's a relatively simple low cost exercise.

 

In the heating season, the trade-off between introducing uncontrolled cold air from outside via a myriad of leaks and pushing out warmed air through a positive internal pressure is difficult to evaluate but having a system you can control should provide some advantage. Admittedly it would the kind of thing that would benefit from a degree of DIY electronics - monitoring CO², temperature and humidity and developing a control algorithm.

 

My own musings revolve around installing a fan unit in our loft feeding filtered air into the airing cupboard that houses our HW cylinder and venting out into our central hallway. The waste heat available would deplete quite rapidly on cold days (have to do some calcs) but a small resistive heater as a PV diverted load could cover some of the requirements.

[SteamyTea]

23 minutes ago, Radian said:

single PIV loft type fan

Due to my house layout, basic 2 up, 2 down terrace, the easy solution is to fit a lift unit and plumb in the pipes upstairs in the traditional manner, then fit a large, through the wall dMVHR for the kitchen.

The living room has the stairs in it, so the landing is  in effect  the same room.

I could put some pipes in between living room ceiling and the bedrooms, but not really worth the effort.

[Radian]

36 minutes ago, SteamyTea said:

I could put some pipes in between living room ceiling and the bedrooms, but not really worth the effort.

Shaving a bit off the bottom of bedroom doors is my plan for that.

[SteamyTea]

Just now, Radian said:

Shaving a bit off the bottom of bedroom doors is my plan for that.

That isn't the issue in my idea.

Not having an inlet or outlet in the actual living room is the problem.

May be able to pipe through bathroom and airing cupboard.

[Radian]

42 minutes ago, SteamyTea said:

The living room has the stairs in it, so the landing is  in effect  the same room.

 

 

2 minutes ago, SteamyTea said:

Not having an inlet or outlet in the actual living room is the problem.

Isn't that the obvious answer?

[SteamyTea]

4 minutes ago, Radian said:

Isn't that the obvious answer

Not really as there is no fresh air entering the living room, just stale air dragged upstairs.

[Radian]

2 hours ago, SteamyTea said:

Not having an inlet or outlet in the actual living room is the problem.

 

But just how airtight is the room in reality? Have you measured the ACPH? My rooms all leak like a sieve mostly around windows and electrical fittings. The skirtings to floor are mostly OK and I'm going to re-caulk the windows but trying to seal the electrics on dot & dab plasterboard is virtually impossible.

[Iceverge]

Installed MEV in my parents house in the upstair landing. Just extracting from one location. 

 

No measurements taken but it has reduced dampness and mould in the whole house . The house is very leaky. 

 

I figured it was the same as PIV in reverse but at least it wasn't dumping a single column it cold air on everyone and was giving the moist air a controlled path to outside rather then being pushed through the building fabric. 

 

So long as room doors get opened semi regularly I think it isn't too much of an issue not ducting every room.

 

 

 

 

[S2D2]

My chosen solution for a similar situation was PIV - I couldn't justify the running costs of MVHR with such a leaky, albeit reasonably "not too bad" house. I have block + beam + block walls so was less worried about moisture escape, though my previous house was timber frame and used PIV to similarly good effect. Installed above double height stair void and temperature is vaguely noticeable when passing but far warmer than outside on a low setting and nothing that makes me wish it wasn't there, I don't loiter on the stairs. Air quality much improve at a subjective level, I never bothered measuring it as I considered the problem solved.

[jayc89]

On 26/10/2022 at 20:34, S2D2 said:

My chosen solution for a similar situation was PIV - I couldn't justify the running costs of MVHR with such a leaky, albeit reasonably "not too bad" house. I have block + beam + block walls so was less worried about moisture escape, though my previous house was timber frame and used PIV to similarly good effect. Installed above double height stair void and temperature is vaguely noticeable when passing but far warmer than outside on a low setting and nothing that makes me wish it wasn't there, I don't loiter on the stairs. Air quality much improve at a subjective level, I never bothered measuring it as I considered the problem solved.

 

If you were to do it again, where would you install the PIV if not after the stair void?

[S2D2]

2 hours ago, jayc89 said:

 

If you were to do it again, where would you install the PIV if not after the stair void?

Assuming a loft installation your only real option for a standard house design is the upstairs landing. It is not silent so you don't want it in a bedroom and you want to create a pathway from input to extract, usually in bathrooms, so it can't go in those either.

 

You can usually get quarter baffles to stop it creating a draft in a particular direction if it is at normal ceiling height and one aspect gets more usage than the others.