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Community and Q&A

Ducted HRV, Lunos e2 or Extraction only

build2580 | Posted in Mechanicals on

Thanks in advance for your knowledgeable advice. I understand just enough about air sealing, heat recovery, and ventilation to be completely confused as the best way to go about ventilating the house I am currently building. This house is a very small (700 sq ft./64 m2) open plan, one bedroom/one bath strawbale house with a small loft and a simple raked ceiling. I am attempting to build it very tight, but won’t have actual figures on that until after the first coat of render and blower door test in April or so. I do need to consider electrical runs and potential ducting now.

My priorities are good air quality and thermal comfort with minimal energy use, ideally at the best value for performance. I thought I would use a pair of the Lunos e2 units, but am now wondering if they would be enough to not need additional bathroom or kitchen extraction? If so, is adding other extraction a problem with the Lunos e2 system? If I needed additional extraction anyway, could I get by with just extraction? If so, how sould I configure such a system (bathroom/kitchen extraction, whole house unit, etc)? Or is a ducted HRV a better option, although it seems a bit of overkill to me?

I do not need a fully automated system. I am happy to have opening of windows and doors as a part of my ventilation strategy, but also want to have fresh air on days over 35C/100F and during winter.

On such a small build, it is things like this that can potentially cost a disproportionately huge amount of money. I am willing to invest what I need to for a good outcome, but I don’t want to blindly go down a more expensive/complicated road than necessary just because most information out there is geared toward a much larger building.

If reply included brand names of recommended products, that would be fine by me (or at least the technical details I should look for in a product)!

Thanks again!

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  1. charlie_sullivan | | #1

    On the one hand, this sounds like a great application for Lunos. Their latest product which has two fans in one unit, can do an exhaust-only mode, if you want that function for a bathroom, for example.

    On the other hand, a lot of the expense in a conventional HRV system is ductwork...and maybe you don't need much of that. Exhaust from the bathroom and kitchen and maybe just one supply vent. And since you are building new, it is not too hard to do that.

  2. GBA Editor
    Martin Holladay | | #2

    For a very small house like the one you describe, I think that a single Panasonic exhaust fan in your bathroom is all you need. Run the fan for as few or as many hours as you think you need.

    For more information on exhaust-only systems (as well as your other ventilation options), see Designing a Good Ventilation System.

  3. build2580 | | #3

    Thanks Charlie and Martin,
    Yep, it was reading the Good Ventilation System post that made me start rethinking my strategy. I am happy with the ease and simplicity of needing only a bathroom extraction fan. Rarely does a change of plans lead to something more simple or less expensive- yippy! However if I go to all this trouble to make a tight house, is it not then odd to add an extraction only system without any intake or heat exchange? Maybe I only worry about that if my blower door test comes out amazingly well!

  4. build2580 | | #4

    oops one more.... OK to ignore extraction in the kitchen?

  5. GBA Editor
    Martin Holladay | | #5

    It's your house. You can do what you want (as long as you meet local building code requirements).

    If you want a kitchen range hood / exhaust fan (or are required to install one), you can use it as often or as rarely as you like. A lot depends on what type of cooking you do. It almost never makes sense to use a kitchen range hood fan for whole-house ventilation.

    For more information on range hood fans, see Makeup Air for Range Hoods.

    Q. "If I go to all this trouble to make a tight house, is it not then odd to add an exhaust-only system without any heat exchange?"

    A. For more information on this topic, see Are HRVs Cost-Effective?

  6. build2580 | | #6

    Site was acting strange last night and appears my last response didn't make it.

    So, I had already read the links you suggested and have now also read all of the 100s of comments. I am far wiser in theory and still uncertain of what to do for my little project. Not meaning to be completely thick here, but I am limited in having an educated opinion in that I have never lived in a well sealed house. The normal house here is more like swiss cheese and would make a typical American home look like a sealed safe. So, assuming I build it all well, will an extraction only system be comfortable, or will I be pulling in too much cold/hot/dusty air? Will the Lunos circulate enough air in the bathroom and kitchen to not need any extra extraction? In hindsight, I am sure I will have a strong opinion, I would like some foresight from someone that has first hand experience with these options. As far as regulations- no worries, we have no ASHRAE or similar to conform to (although the Lunos would meet those demands for my small space). As far as cooking mentioned above- pretty basic, no meat. There will probably be a mini-split installed and the only combustion appliance is a range hood. So, if this were your house, what would you do?

  7. GBA Editor
    Martin Holladay | | #7

    I'm not sure what you are saying. Are you used to living in drafty houses?

    If you build a relatively airtight house, it's good to have a ventilation system. Most people who live in small, open-plan houses are satisfied with the performance of an exhaust-only ventilation system. Most people who install Lunos fans are satisfied with their operation.

    If your house seems drafty, seal the air leaks. If your house feels over-ventilated, turn off the exhaust fan. If your house feels stuffy and humid, turn on the exhaust fan.

    In other words, you can have control over how you operate your ventilation system.

  8. build2580 | | #8

    Yes, I am used to living in drafty, uninsulated, single glazed, poorly oriented, etc houses. In other words the typical house in my area. As I am building a new house, I have spent endless amounts of time trying to educate myself on how to get it right. This website has been a wealth of information. I thank you and all of the contributors for that. There may be some restriction on what or how you can advise that prevents a direct answer to "if this were your house, what would you do?" but that is fine. I will take the info I have and make a decision. Thanks again.

  9. ntisdell | | #9

    Depending on the amount of time you are home, how much cooking you do on the stove, how many times people shower (or go #2) with the exhaust fan on or off, all effect your need for ventilation.

    However, one thing to note regarding ventilation requirements for a small house - is that in a 2700sqft home each time the exhaust fan runs for 20minutes or each time you open the door it maybe isn't that much fresh air as a % of total home air volume. However when you have a 700sqft house , each of those occurrences (which happen every day at regular intervals) are quite a bit more significant(4x in fact ).

    Timely 'flushing' (open windows or run exhaust) of your home (warm front in winter on a sunny day, cool front in summer, open windows most of the spring/fall) will also help negate energy losses.

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