Ventilation plan for period house

[Benjseb]

We’ve got a barn conversion, 250sqm. OK insulation that we’re graduallly improving as we go. 
 

No loft space!

 

We’ve recently sealed it up quite a bit by replastering everywhere and replacing and sealing all the kingspan in the “room in roof” upstairs. Insulated floors, etc and are looking at replacing a few older doors to tighten them up. 
 

I’m keen to ensure it’s properly ventilated, to keep it healthy and avoid any mould (so far so good)  I’m a health coach so value clean fresh air! We don’t have any visible condensation but humidity tends to sit around 65%, sometimes more, and I’d prefer it down around 50-60% to keep dust mites at bay, etc. 
 

Current setup: 

 

So far we have a trickle extractor in each wet room plus downstairs WC and utility. So 4 rooms in total (@6l/s each)

 

All upstairs rooms have velux so built in trickle vents, and downstairs windows I’ve just made sure have at least a 1700mm2 vent in each window so less than regs but better than they were. 

 

Just looking at this year and I’d like to potentially upgrade this a bit (building regs are 0.3 l/s/m2 = 75l/s vs our current 24l/s but admittedly we will have leakage increasing this so won’t be aiming for 75)

I’d like to also recover some of the extracted heat loss if possible to keep costs down. Our heating bill is about £1200/yr. 
 

So far my thinking is as follows: 

 

* In the 2 en-suites keep this as constant trickle extraction to avoid the “cold draught” of single room MVHR)

 

* In the downstairs WC and Utility replace with Vent Axia Tempra heat recovery extractors. 
 

Questions:

 

* In the downstairs WC we also have our DHW and buffer tank for heating so that room is probably +3c. Would it be better to install a PIV unit in this room to force that warmer air in through the house? It’s fairly central. With there being a toilet in that room I guess it needs to extract on demand too though which cuts down on our options. Is that over thinking or do we just put a heat recovery extractor in?

 

* Is it best to have a combination of extract and PIV or just rely on extract with window trickle vents?

 

Overall I want to avoid stuffiness/humidity with fresh air but without costing the Earth in heating. I really wanted something a bit more “joined up” but with no loft space not many options. 

 

I can’t really get any straightforward advice as most companies just want to flog whatever they sell rather than the right solution! 

Edited August 18, 2020 by Benjseb

[Mr Punter]

Could you have an air leakage test done cheaply?  You could then work out where most of the uncontrolled leakage is.  The extract rates seem rather low.  Can you increase them?  Maybe double or triple.  In the plant room you could just have a light switch or pull cord fan.  I doubt if heat recovery will make much difference to your bills.  What is you heating fuel?

[Benjseb]

8 minutes ago, Mr Punter said:

Could you have an air leakage test done cheaply?  You could then work out where most of the uncontrolled leakage is.  The extract rates seem rather low.  Can you increase them?  Maybe double or triple.  In the plant room you could just have a light switch or pull cord fan.  I doubt if heat recovery will make much difference to your bills.  What is you heating fuel?

 

I did consider an air leakage test. Will look into it

 

Most of the dMEV units are either 6 or 9 l/s. Above that it gets noisy. There might be other units but I have a feeling they will need 150mm holes in the wall which we don’t have. Could make them bigger but I imagine quite tricky to do so through 60cm of stone. 

[Mr Punter]

Is the high humidity throughout the building and throughout the day / year?  Have you looked at a dehumidifier instead of increasing ventilation?

[Benjseb]

16 minutes ago, Mr Punter said:

Is the high humidity throughout the building and throughout the day / year?  Have you looked at a dehumidifier instead of increasing ventilation?

It generally tracks about 10% higher throughout the year. It will do due to us having no DPC so ventilation is just part of the strategy. 
 

Dehumidifier is an option, especially in winter, but I think needs to be coupled with ventilation really as that has its own merits too. Stale dehumidified air is still stale ?
 

lots of people getting decent results with PIV in older houses to lower humidity but without a loft it’s quite hard. But could do this in certain rooms as explained. 

Edited August 18, 2020 by Benjseb

[Ferdinand]

Can you lower the ground level outside by say 300mm to help the walls be a little dryer?

 

My standard strategy in restoring period rentals is to use heat recovery or DMEV fans with a trickle setting - as you outline, and then have a PIV fan in the roof to help out.

 

In my own warm roof dormer bungalow house I have the PIV installed in the leftover toblerone roofspace on the landing where the low wall blends into the ceiling.

 

Alternatively can you have a powered or manual rooflight that opens for 10-15 minutes in the morning?

 

F

Edited August 18, 2020 by Ferdinand

[Ferdinand]

Further thought.

 

How well is your distribution set up between rooms?

Will it make your trickle fans more effective if you had eg 8mm gaps under your internal doors?

[Benjseb]

51 minutes ago, Ferdinand said:

Can you lower the ground level outside by say 300mm to help the walls be a little dryer?

 

My standard strategy in restoring period rentals is to use heat recovery or DMEV fans with a trickle setting - as you outline, and then have a PIV fan in the roof to help out.

 

In my own warm roof dormer bungalow house I have the PIV installed in the leftover toblerone roofspace on the landing where the low wall blends into the ceiling.

 

Alternatively can you have a powered or manual rooflight that opens for 10-15 minutes in the morning?

 

F

 

we have a cobbled courtyard on one side, which will be a pain to solve but longer term can dig a french drain. The other side is a flower bed which obviously isn’t ideal. So planning on digging say 9” away from wall and filling with gravel once things start to die back. 
 

We do have Integra Velux so it’s set to open automatically to regulate humidity but tends to only be 10-15 mins in the winter. Just not sure how much that air gets drawn downstairs (which is where the higher humidity is) as I presume any pressure differences get obliterated once the velux open and it’s probably just air flowing from one velux to another. 
 

I’ve  blocked up the trickle vents in the wet rooms so that the air gets sucked from other rooms and last weekend took 15mm off most of the internal doors. 
 

just concerned about 4 fans doing 6l/s... will that actually make any difference in a 250m2 house? If not then I’m not sure where else I can put a fan due to noise etc. 

[Mr Punter]

Put the dehumidifiers x2 downstairs.  They also add some heat.  Have trickle vents in the downstairs windows and extracts upstairs.  The gap under doors works well to allow easy air flow.

[Benjseb]

Decided to go for the Vent Axia Pozidry compact Pro PIV downstairs, with the existing dMEV fans in wet rooms upstairs. 

 

Going to fit it in our plant room which is central in the house and has the hot water tanks so sits a couple of degrees warmer. Hopefully will take the edge off the incoming cooler air. 
 

It’s downstairs where the humidity is higher so hopefully will get the air moving around and can reuse an existing 100m wall vent. 
 

Arrives  tomorrow so will see how it goes. We may need another somewhere due to size of house but will see...

Edited August 24, 2020 by Benjseb

[Ferdinand]

My only q there is does PIV work downstairs to upstairs?

 

Never tried it so I don’t know.

 

ATB anyway.

 

F

[Benjseb]

I was told the flat units need to be installed one upstairs and one downstairs so starting downstairs. 
 

I don’t think it makes much difference, if it’s mainly working by pressurisation. In my head, if humid air rises as it’s less dense then putting a PIV on the top floor ceiling would potentially push that humid air down? But probably overthinking. I reckon they just put them there due to the convenience of the loft space. 

[Benjseb]

PIV is in and running. Noticed quite a change already. 
 

The downstairs is probably 10-15% lower RH than it was before, depending upon the weather we’re sweating between 50% and 60% consistently now, rather than 60-75%
 

A success I’d say. It’s underpowered for the size of house (250m2) but I’m using it more as a way of inputting fresh dry air in a controlled manner, rather than worrying too much about there being a specific positive pressure. 
 

Does the trick!

[tonyshouse]

It will blow a lot of your heat and money out through all the cracks when it gets cold, like setting fire to pound notes

 

yes it works nut the cost is HIGH 

[Benjseb]

Well yes that colder air needs warming. But if the humidity in the house is 10-15% lower there’s a lot of energy that won’t be wasted as latent energy heating up water vapour. 
 

Also, any house needs ventilation. Whether that comes in through cracks, uncontrollably, or whether it’s blown in via PIV, controllably, there has to be air movement. Id personally prefer to draughtproof the house as much as possible and then have PIV+dMEV which I can turn up /down as I please. 
 

Anyone done the sums to compare?

[Ferdinand]

 

I asked this a year ago, and @SteamyTea kindly supplied the calculation method for heat loss of warm air in continually running trickle-fans.

 

It turned out that for me my ufh heating system and level of heat demand is such that it tipped it over into making the heating system insufficient, so I switched my fans back to traditional "one with the lights in the bathroom and a 20 minute timer afterwards".  It is a bungalow to dormer bungalow self build project doe by the previous occupier - better than regs when done but insufficient insulation for this latest ventilation intervention. 

 

You could switch your Dmev fans for trickle/boost HR units which would recover 80-90% of the heat lost.

 

Here:

The numbers were approx £25-30 per year on the gas heating bill for each DMev fan running at 6 l/s. But you need to read the thread.

And since mine is a recent comprehensive (3 walls and a hole in the ground) self-build reno, it *should* be reasonably airtight. In other circs the loss of heat through wall leakage etc could be more than the fans.

 

If you really wanted to you could also calculate the extra cost to heat up the extra water vapour in the more humid air ?.

 

For me comfort was the determinant rather than the extra charge as I was nursing my mum (who passed away last November), and I wanted the house as warm as possible. I may reevaluate in due course. I have at least one where I could install a Heat Recovery unit, whilst the other is in the ceiling of bathroom 2.

 

And I agree with Tony that working on improving airtightness is important - I always make my tradesman pay real attention to detail.

 

Ferdinand

Edited September 6, 2020 by Ferdinand