Adding ventilation to an old home (when insulating)

A recent HOL post:

Your energy is cheap

discussed insulation of old homes and cautioned about ventilation issues.

I wanted to share a bit of our story, this part specifically about ventilation.

Background

We purchased an old home on the ladder two years ago.  The estate agent brochure for the house contained a picture similar to the following:

The hint is the electric radiator in front of the the gas-fired hot water radiator.  This house was freezing.

We wanted to refurbish the basement and ground floor of the property to improve the main living space.  We didn't have budget to do the entire house, so we optimistically called the work we've done so far "Phase I".

We brought in an energy consultant (Green Tomato Energy) for an energy survey of the house.  They have experience with renovating old British homes to stringent PassivHaus regulations.  (e.g. Lena Gardens Passive House – Project ID 2033)

We knew that we didn't have budget to bring the house up to PassivHaus spec (which is basically no net energy input), but we found it useful to use some of their modelling techniques and expertise to understand what we needed to improve.

Windows were a big area for improvement -- when the wind blew, even if the windows were 'shut' the curtains would move.  We decided after the review that we would replace all the windows in the house with more energy efficient and airtight units.  These would be triple-glazed units for bedrooms and north-facing rooms.  We used double glazing for warm living areas facing south as it was cheaper for some of the large expanses of glass and theoretically it allows for more passive solar energy to enter.

We specifically did not want to spend money on energy efficient windows but then be forced to get them with trickle vents as is often the standard in the UK in order to comply with building regs for air quality.

One of the other major areas identified (aside from the usual suggestions about loft insulation which we decided to postpone for Phase II) were the chimney stacks in each corner of the house.  Although we specifically did not want to touch the upstairs, we were told that it would be cheaper to remove these all the way up to the top, rather than attempt a solution at the bottom of the house while leaving them in place.  Opening these up proved a revelation.  While sealed to the room, usually these were still open to the sky:

So imagine 2 or 3 columns of cold air holding each corner of your house from top to bottom.  If your house is on The Ladder, this is probably also what's going on behind your walls.

Removing these chimney breasts did involve some upstairs work to repair the newly created gaps, but increased space in each room. 

Ventilation

As a commenter mentioned in the HOL post, insulating and increasing air tightness can cause problems in old houses, for example with condensation, unless you take steps to ensure you have proper ventilation.

To address this, we ran air circulation tubing to each room of the house.  This would remove stale, humid air with intakes from the kitchen and bathrooms, with fresh air outlets in each of the bedrooms and lounge.  We chose AirFlow Airflex PRO tubing because it was cheap to install -- you could run a single tube from each room down to the utility room.

As much as possible, we used the gaps from removed chimneys to start routing ventilation throughout the house.

We also used the gaps from former chimney breasts to run tubing for future roof-mounted solar hot water heat collectors (Phase II).

All of these tubes were routed into a central utilities area in the basement:

They then found their way into a couple of collector boxes, one for fresh-to-rooms and one for stale-from-baths-and-kitchen:

These then fed into a Mechanical Ventilation Heat Recovery unit.  These seem a bit difficult to get in the UK.   You can go *really* fancy on these with refrigerant heat pumps, etc., but we chose a simple fan-only Vaillant RecoVAIR 350 .   We went with Vaillant because it was a brand our builder was familiar with for boilers.   (not yet shown connected in this picture):

Fresh air is sucked into the heat exchanger unit through tubing which was passed underground below the newly poured basement foundation.  Running it through the earth means the cold air from outside is slightly heated already in winter and slightly cooled in summer:

The MVHR isn't that complicated.  It's basically two fans -- one pulls stale air past some metal vanes before exhausting it out the house.  The second is sucking fresh air from outside and pushing past the other side of the vanes and then it into our rooms.

This system isn't meant to heat the home -- we still have hot water underfloor heating in the ground floor and (now much smaller) hot water radiators upstairs. 

While perhaps a little unusual for the UK, in Canada, forced air heating of homes is pretty standard and for the past few decades a heat exchanger setup for extracting heat from stale air and using it to pre-warm fresh incoming air before it reaches the furnace has been a standard building code requirement.

This is how we ensured each room got a supply of fresh, filtered air. It provided a way to remove steamy air from showers or cooking without a direct-to-outside holes in the wall, instead allowing us to use that warmed air to heat incoming fresh air from outside the home.

It also allowed us to meet building safety codes for ventilation requirements without the usual trickle air vents in all the new windows we purchased.

Results after Phase I

I'll leave a discussion of the insulation and windows for another time if people are interested.

The previous owner of the property (note: also Canadian so I contributed no net Canadianness to the borough when I moved in, for those against immigration ) was diligent enough track his energy usage and kind enough to share this data with us.

The house used to have peak gas heating usage around 130 - 140kWh/day in winter.  Last winter we found our heating usage was about 80kWh/day with a max of 93kWh/day on some of the really cold weeks.

I consider that a reasonable result given that we haven't insulated back walls of the house or touched the roof yet (it has some insulation).

We find the house's air quality is great, without needing to open any windows.  We don't experience drafts in the house.  We find that the whole central living space of the house is warm and comfortable, whereas we know that previously the owner had to close the front and back receptions in winter because these were simply too cold.

Hope that's useful...