The simpler the better!

[WelshMatt]

Hi there!

 

I haven't managed to find a plot yet but for the past few months I've been designing the perfect home for my partner and I.

I want it to be as "eco friendly" as possible but I'm not fussed on the technology that's used in home nowadays (ASHP's & MVHR's). That's why I've focused on a small footprint with lots of airflow around the house and just a wood burner as the main heating source for the winter. I am considering electric underfloor heating in the bathroom if needed. The shell will be made from SIP panels and will be clad in cork rather than a traditional brick, render or timber cladding. I'll also have a Solar Assisted Heat Pump for hot water as it has less moving parts than an ASHP and is ample just for our hot water use.

 

My main stumbling block now is whether the ventilation system I want is adequate (I think it is but have no real experience apart from research online). Rather than a MVHR I've gone for a PIV system to pump in the fresh air and some old fashioned vents to exhaust the stale air. I'll be relying on air currents to transfer the heat and fresh air around rather than tons of ducting.

 

I've attached a pic to show my ideal layout and some of my ideas.

 

Anyone have any experience with this type of low tech build here?

[SteamyTea]

13 minutes ago, WelshMatt said:

just a wood burner as the main heating source for the winter

A wood burner is anything but eco friendly.

[WelshMatt]

🤣 I knew someone would point that out but I beg to differ as it will be rarely be used as the home will gets most of its heat from passive solar through the windows and stored in the floor. Any wood that is used will be sourced locally and modern wood burners if used correctly burn off most of the harmful gasses before they go up the flue.

Think how much has gone into making an ASHP in terms of mining all the rare metals for the components, the materials for all that piping that had to be laid etc. 

The wood burner is here to stay.

[ToughButterCup]

38 minutes ago, WelshMatt said:

...

Anyone have any experience with this type of low tech build here?

 

Hi, welcome.

No. No direct experience, but I remember researching the issue when I was at your stage of a build. There is plenty of well-researched, peer reviewed stuff.

 

38 minutes ago, WelshMatt said:

...

I'll be relying on air currents to transfer the heat and fresh air around rather than tons of ducting.

...

 

There's the key issue. (from remembered reading..... subject area 'passive ventilation') Dead spots are very hard to identify without extensive modelling. Air flows are not instinctively predictable.

 

I'll try and dig out the research papers

 

PS

Found it .....

https://www.sciencedirect.com/science/article/abs/pii/0360132389900024

 

Edited May 5, 2022 by ToughButterCup

[ProDave]

Most people on here have experience of low energy houses "it's what we do"

 

Wood burners are a marmite subject.  I have one and use it mainly because we have trees and free wood.  If I dod not burn it I would be giving it away to someone else to burn.  If i had to buy all my wood I am not sure.  Please don't kid yourself they are eco friendly.  Some people seem to think that the CO2 that goes up the flue from a WBS is somehow "good" CO2 but to me it is just the same as if you were burning gas or oil.

 

A WBS is a single point of heat (unless it heats hot water) so your problem for whole house heating is moving that heat.  We find with a 2 storey house with a central stairwell that is easy, but less easy to move the heat around a single storey dwelling with lots of walls.

 

Once you get a building very well insulated you find if you do the sums that ventilation heat loss dominates, which is where MVHR is good because it eliminates most of the ventilation heat loss.  PIV just draws cold air in from outside and expels warm stale air

 

Whatever you do, I would put under floor heating pipes in.  Then if you find your passive heating does not work as you expect you can add another heat source such as an ASHP.  It would be a major job to fit UFH later on.  Some on here have such a low heating need they just use a Willis heater (immersion heater in a tube) to heat their UFH

[joth]

Welcome!

 

1 hour ago, WelshMatt said:

My main stumbling block now is whether the ventilation system I want is adequate (I think it is but have no real experience apart from research online). Rather than a MVHR I've gone for a PIV system to pump in the fresh air and some old fashioned vents to exhaust the stale air. I'll be relying on air currents to transfer the heat and fresh air around rather than tons of ducting.

 

 

The question is not just if it's adequate in practical terms, but also if it meets building regs and your stated goal of being as eco-friendly as possible

 

The problem with old-fashioned vents is when it's windy outside they allow all the heat to be blown out of the building at an uncontrolled rate. Further, if you build with PIV and vents then there's no point investing time and money into building the rest of the house in a highly airtight fashion, being you'll have uncontrolled heat loss all over the building when there's any wind at all outside. That heat will need replacing by burning up wood at a greater rate than you otherwise would have, thus far from being as eco-friendly as possible.

But if you build an airtight house, PIV simply won't work, and won't be signed off.

 

And PIV requires an electrical motor running 24/7 so in terms of technology and electricity dependence you're already more than zero, so why not recover the heat too?  I'd keep an open mind, you're very early in the process to be trying to optimize away a couple lengths of ducting. 

 

[ProDave]

That''s another good point about air tightness.

 

Check what the building regs say where you are. Another builder near me was set on PIV but then he had his air tight test done and the result was "too good" so building control insisted he fit mvhr, which was a lot harder part way through the build.

 

It would seem insane to deliberately make your air tightness worse just so you can use PIV.

 

Also the stove if you are going to fit one, choose one that is "room sealed" i.e. it draws it's combustion air direct from outside through a duct, not from the room.

[joe90]

I am the forums Luddite, I don’t do tech and had a similar approach to your plans. You only buy insulation once so buy a lot. I also have a woodburner, yes controversial but like @ProDave I burn my own wood and frankly it’s only used a couple of months a year. I also have MVHR but mainly so I did not have to have trickle vents wasting warm air and creating draughts. I bought mine on EBay cheap. Installed it myself and never got round to balancing it and the house is very comfortable. Yes orientation is key IMO, my house faces South and with a large conservatory this heats my house for the majority of the year. I do have an ASHP again from Ebay with UFH all installed myself. The only thing I did not do is install PV but with current price hikes this is now on the cards on my  workshop roof (again facing south). Keep asking questions, lots of practical knowledge here 👍

 

 

 

[SteamyTea]

33 minutes ago, ProDave said:

Some people seem to think that the CO2 that goes up the flue from a WBS is somehow "good" CO2 but to me it is just the same as if you were burning gas or oil.

Not just CO₂ though.  Wood burners emit particulates at a higher level than diesel engine.

 

Still, everyone I know with wood burners are more than happy for me to come around, in my EURO4 diesel car, and smoke a pack of Marlboro in the front room.  They encourage it in fact.

Edited May 5, 2022 by SteamyTea

[ToughButterCup]

1 hour ago, SteamyTea said:

... and smoke a pack of Marlboro in the front room...

 

while blowing your smoke up the chimney ?

 

[SteamyTea]

6 minutes ago, ToughButterCup said:

 

while blowing your smoke up the chimney ?

 

That would be a waste.

[WelshMatt]

2 hours ago, ToughButterCup said:

 

Hi, welcome.

No. No direct experience, but I remember researching the issue when I was at your stage of a build. There is plenty of well-researched, peer reviewed stuff.

 

 

There's the key issue. (from remembered reading..... subject area 'passive ventilation') Dead spots are very hard to identify without extensive modelling. Air flows are not instinctively predictable.

 

I'll try and dig out the research papers

 

PS

Found it .....

https://www.sciencedirect.com/science/article/abs/pii/0360132389900024

 

Thanks. I'll take a look at that but I feel I may have underestimated the need for a MVHR in a air tight build judging by all the comments so far!

[WelshMatt]

2 hours ago, ProDave said:

Most people on here have experience of low energy houses "it's what we do"

 

Wood burners are a marmite subject.  I have one and use it mainly because we have trees and free wood.  If I dod not burn it I would be giving it away to someone else to burn.  If i had to buy all my wood I am not sure.  Please don't kid yourself they are eco friendly.  Some people seem to think that the CO2 that goes up the flue from a WBS is somehow "good" CO2 but to me it is just the same as if you were burning gas or oil.

 

A WBS is a single point of heat (unless it heats hot water) so your problem for whole house heating is moving that heat.  We find with a 2 storey house with a central stairwell that is easy, but less easy to move the heat around a single storey dwelling with lots of walls.

 

Once you get a building very well insulated you find if you do the sums that ventilation heat loss dominates, which is where MVHR is good because it eliminates most of the ventilation heat loss.  PIV just draws cold air in from outside and expels warm stale air

 

Whatever you do, I would put under floor heating pipes in.  Then if you find your passive heating does not work as you expect you can add another heat source such as an ASHP.  It would be a major job to fit UFH later on.  Some on here have such a low heating need they just use a Willis heater (immersion heater in a tube) to heat their UFH

Thanks for replying. I guess that if I do have MVHR then a wood burner should be more than sufficient for a 100m2 fairly open plan build I guess. We don't like a warm house as we have 2 big dogs who hate the warmth as do we. I live in a leaky stone built house at the moment and only have the heating on between Dec-February usually so am very cold tolerant. As long as I get the ventilation right so there isn't any damp of pollutants then I'll be happy.

I get what you mean about installing UFH just incase but I can't bear the thought of all those plastic pipes sitting there not being used.

[WelshMatt]

1 hour ago, joth said:

Welcome!

 

 

The question is not just if it's adequate in practical terms, but also if it meets building regs and your stated goal of being as eco-friendly as possible

 

The problem with old-fashioned vents is when it's windy outside they allow all the heat to be blown out of the building at an uncontrolled rate. Further, if you build with PIV and vents then there's no point investing time and money into building the rest of the house in a highly airtight fashion, being you'll have uncontrolled heat loss all over the building when there's any wind at all outside. That heat will need replacing by burning up wood at a greater rate than you otherwise would have, thus far from being as eco-friendly as possible.

But if you build an airtight house, PIV simply won't work, and won't be signed off.

 

And PIV requires an electrical motor running 24/7 so in terms of technology and electricity dependence you're already more than zero, so why not recover the heat too?  I'd keep an open mind, you're very early in the process to be trying to optimize away a couple lengths of ducting. 

 

Very valid points mate.

I think I'll have to accept that MVHR is necessary and get over the fact that PIV just won't be sufficient for building control 😒

At least on the brightside I can do away with the vents above the bedroom doors, bathroom extractor fan, the outside vents in the bedrooms as well as the cooker hood outdoor extraction!

[WelshMatt]

1 hour ago, joe90 said:

I am the forums Luddite, I don’t do tech and had a similar approach to your plans. You only buy insulation once so buy a lot. I also have a woodburner, yes controversial but like @ProDave I burn my own wood and frankly it’s only used a couple of months a year. I also have MVHR but mainly so I did not have to have trickle vents wasting warm air and creating draughts. I bought mine on EBay cheap. Installed it myself and never got round to balancing it and the house is very comfortable. Yes orientation is key IMO, my house faces South and with a large conservatory this heats my house for the majority of the year. I do have an ASHP again from Ebay with UFH all installed myself. The only thing I did not do is install PV but with current price hikes this is now on the cards on my  workshop roof (again facing south). Keep asking questions, lots of practical knowledge here 👍

 

 

 

Do you find that you need to use your ASHP for room heating as well as the wood burner or is it used mainly for the hot water?

 

And yes the house will be super insulated with the SIP panels and will face south.

[joe90]

15 minutes ago, WelshMatt said:

Do you find that you need to use your ASHP for room heating as well as the wood burner or is it used mainly for the hot water?

 

And yes the house will be super insulated with the SIP panels and will face south.

The ASHP runs the heating fir about 3 months of the year max and only coming on fir a few hours a day, it keeps the floor at about 22’ which stops the house feeling cold, for a blast of heat in winter i light the woodburner. The ASHP runs for about an hour a day to top up the DHW cylinder. If and when I get PV, I will time the ASHP to start at 11 am to use any excess sunshine (if). If during the winter this timing is not enough I will over ride it.

[SteamyTea]

MVHR uses relatively small bore pipes and low flow rates.

If you really want to shift thermal energy about, and control it better, fit larger pipes.

Double the diameter and you quadruple the mass flow rate at the same velocity.  Means you can shift 4 times the energy as well.

Carefully designed at the start, it need not be visually intrusive.

With improved airtightness you have to consider condensation.

Think of a airtight plastic box. It can sir there all day and night with no condensation forming, but drop the container temperature a few degrees and the water vapour condensed in the container.

This is basically what an airtight house is.

To get around this, external air is introduced, this, generally in the UK has a lower absolute amount of water vapour in it than internal air (2 people produce about 4 kg of water vapour a day, dogs a lot more relatively).

The old way to keep condensation under control was to crank up the heating, this keeps the water as a vapour, not a liquid.

Trouble with this is that higher temperatures mean higher losses, not only through air losses, but also through conductance through walls, floors, roofs, windows and doors. Small houses have a disproportionately higher surface area to volume, so when measured as losses by total floor area, the numbers look bad.

[joe90]

“At least on the brightside I can do away with the vents above the bedroom doors, bathroom extractor fan, the outside vents in the bedrooms as well as the cooker hood outdoor extraction!”
 

You need 10mm gap under doors for air movement with MVHR, I have a recirculating cooker hood and installed a relative humidistat in the extract manifold (again I made this myself!) which switches the MVHR onto boost mode if excess humidity is detected (bath, shower, cooking) some have a manual button to press to kick in the boost. Using the small diameter flexible pipe is sooo much easier to instal than large rigid pipes (you can always double up the pipe if you want more air movement).

[SteamyTea]

1 minute ago, joe90 said:

you can always double up the pipe if you want more air movement

Only doubles the flow though, but takes up more space.

 

Bedrooms are one place you want to extract air from. 

I have never understood why people sleep with windows closed, and heating off, then in the morning, turn the heating on and open the windows 'to air the room'.

Too late by then.

[joe90]

1 hour ago, SteamyTea said:

Bedrooms are one place you want to extract air from. 

No, extract from damp warm places, bathrooms, kitchens, utilities, input to all other living spaces (according to design specs!).

Edited May 5, 2022 by joe90

[JohnMo]

I tried to extract from the bedrooms as that made sense to me as well, but the plans were rejected, so reverted to the normal supply.

 

With a Sip build you will be quite airtight without trying, so will have no option than go for MVHR.  The building regs do state balanced ventilation, so the option would need PIV and MEV or dMEV.  But that makes no sense, when you can recover the heat.

 

You could move air inside the house with dMEV fans within the internal walls.

[ProDave]

Is it wise spending too much time detailing the house until you have a plot?  I looked at 2 different plots and due to the different sizes, orientation and surroundings, the house I built on each would have been very different.

[WelshMatt]

3 hours ago, SteamyTea said:

MVHR uses relatively small bore pipes and low flow rates.

If you really want to shift thermal energy about, and control it better, fit larger pipes.

Double the diameter and you quadruple the mass flow rate at the same velocity.  Means you can shift 4 times the energy as well.

Carefully designed at the start, it need not be visually intrusive.

With improved airtightness you have to consider condensation.

Think of a airtight plastic box. It can sir there all day and night with no condensation forming, but drop the container temperature a few degrees and the water vapour condensed in the container.

This is basically what an airtight house is.

To get around this, external air is introduced, this, generally in the UK has a lower absolute amount of water vapour in it than internal air (2 people produce about 4 kg of water vapour a day, dogs a lot more relatively).

The old way to keep condensation under control was to crank up the heating, this keeps the water as a vapour, not a liquid.

Trouble with this is that higher temperatures mean higher losses, not only through air losses, but also through conductance through walls, floors, roofs, windows and doors. Small houses have a disproportionately higher surface area to volume, so when measured as losses by total floor area, the numbers look bad.

Thanks for this. Does doubling the size mean double the price? 😬

[WelshMatt]

2 hours ago, joe90 said:

“At least on the brightside I can do away with the vents above the bedroom doors, bathroom extractor fan, the outside vents in the bedrooms as well as the cooker hood outdoor extraction!”
 

You need 10mm gap under doors for air movement with MVHR, I have a recirculating cooker hood and installed a relative humidistat in the extract manifold (again I made this myself!) which switches the MVHR onto boost mode if excess humidity is detected (bath, shower, cooking) some have a manual button to press to kick in the boost. Using the small diameter flexible pipe is sooo much easier to instal than large rigid pipes (you can always double up the pipe if you want more air movement).

The pipe is what worries me most. The flexible pipe is that ridged stuff and I worry that over the years that will get clogged up with dust and hair (our 2 big fluffy dogs produce a lot of loose hair, literally fur balls floating around the place!) and I won't be ae to access it to clean plus the filters getting clogged often.

[JohnMo]

The extract points should be installed with a cone foam filter, that keeps the ducts clean