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Community and Q&A

Venting and cooling the 2nd floor (master bedroom + bath)

eldarchik | Posted in General Questions on

Hello everyone,

As we moving along with our renovation upstairs, I came back to get some guidance on venting and cooling the 2nd floor.


Building on this post:

Quick recap:

With the help of this forum from Martin, Dana and others we did our best to insulate the 2nd floor (it was not new construction, this will be our master bedroom with a large bathroom). Our rafters are 5.5 inches deep, so we did 3″ closed cell, I then as advised here added the 1″ foil faced EPS foam strips onto the rafter edges to add an extra inch, and filled the rest of the cavity with 3.5 Inch of Roxul Batt and. Walls we fully filled with open cell and added 1/2″ XPS ridgit foam board.

Windows: went with Intus tripple pane. Will have 3 total new windows installed shortly.

The rest of the house:

Have not started to do any work on the rest of the house yet, but in the future, as we renovate more, would also like to insulate well and get this home to be as well insulated as we can.

Question to the experts:

Since everything still pretty much accessible, what would be the best air flow system to put in place? I have read many threads here and still confused on what to go with? ERV, HRV? or Exhaust only?
Should the system be concentrated for upstairs with the option to later expand for the whole house? or should i go with the standalone units like Lunos E2? WhisperComfort 40/20 or 20/10 CFM Ceiling Spot Energy Recovery Ventilator? If so, which?

My “old school dad” who is the handy man claims that exhaust fan only approach in the bathroom would be more than enough, however he has not done much research, have not kept up to date on these things and is not considering that the 2nd floor now is pretty well insulated and air tight. He does great work, but needs my “new age” direction in this and guidance. My position, is to get this thing right the first time, I think since we want to live here for some time, we are looking to ensure good air quality first, then the wife is very sensitive when it comes to noise, and lastly budget. I’m willing to spend a bit more on a good quiet efficient system that would serve our needs.

Also, we don’t have central air and would like to install a split system. If I can kill two birds with one stone here, and get recommendation/advice on both things, that would be great.

We live in Northern NJ, the space upstairs is approximately 800sqf (with full bathroom). I can supply pictures, and answer any other questions that would point me in the right direction.


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  1. eldarchik | | #1

    I did forget to mention that elevation here is 500 feet, if this is an important piece of information.

  2. GBA Editor
    Martin Holladay | | #2

    What you call an "air flow system" is usually called a ventilation system (or a mechanical ventilation system).

    GBA has lots of articles on this topic. Here are three you should read:

    Designing a Good Ventilation System

    Revisiting Ventilation

    Ensuring Fresh Air in Bedrooms

    In light of the data published in the third article I listed, I would advise that the best approach for your bedroom would be to install an HRV or an ERV with dedicated ductwork.

    The second best approach would be to install a pair of Lunos fans. Note that many homeowners find that Lunos fans are noisy, especially on high speed.

  3. GBA Editor
    Martin Holladay | | #3

    When it comes to cooling, you need to plan for how you intend to cool the entire second floor.

    Many homeowners end up installing a ducted minisplit, with ducts serving multiple bedrooms. Whether this approach makes sense in your case often depends on whether there is a closet than can house the ducted minisplit unit.

  4. GBA Editor
    Martin Holladay | | #4

    One last comment -- more for GBA readers than for Eldarchik: It's important to finalize your plans for a ventilation system, a heating system, and a cooling system before construction begins.

    Once you've completed your framing changes, air sealing work, and insulation work, it's way too late to ask the question, "Where should I put the ducts?"

    That question needs to be answered during the design phase, using pencil and paper -- not after the remodeling work is all done.

  5. eldarchik | | #5

    Hey Martin,

    Thank you this gives me some direction.

    Won't the HRV or ERV with ducts still be noisy in the bedroom? even if we placed it in the limited attic space above?

    If I do decide to go with the HRV or ERV with dedicated duct work, can you suggest one that would serve only for upstairs? Or are they are all made for a full house?

    Also, regardless of the approach, getting a Exhaust only fan for the bathroom is a must correct? As per your advice in your article I'm leaning towards the Panasonic Whisper Green Exhaust Fan for our bathroom upstairs.

    Now regarding Lunos E2:

    1. Would only 1 pair be enough for a bedroom space that is approximately 500sqf?

    2. Regarding noise, can these units be timed and only run during the day when no one is home? or start up in middle of the night when we are asleep?

    Regarding Cooling upstairs, we only have 1 bedroom upstairs and 1 bathroom (total about 800sqf). So we originally thought only installing 1 ductless split unit for the whole upstairs (Mitsubishi I hear has good units). Do you suggest otherwise?

  6. Expert Member
    Dana Dorsett | | #6

    A single pair of Lunos e2 is good for 22cfm at high speed. ASHRAE calls out only 5cfm per person even for hotel bedrooms (you can usually do fine with less), so I think you're good there.

    At high speed you'll be able hear the e2 pausing as it changes direction if it's located next to the bed. It's not loud (your spouses breathing might be in the same range- louder if he/she snores :-) ) but some people may find the few seconds of dead silence at 70 second intervals annoying. At low speed it's extremely quiet.

    If you don't have an exhaust fan for the bathroom it can still meet code with 20cfm of continuous exhaust ventilation. It would be fine to put half the Lunos pair in the bath, the other in the bedroom to have at least some continuous ventilation, and use the exhaust fan only as-needed. It doesn't take much door cut at the threshold to guarantee 22cfm of ventilation air without much pressure drop even with the door closed. When the exhaust fan is running it would take a good fraction of it's make-up air via the Lunos in that configuration, which is fine.

    Mitsubishi is a first-tier vendor, but not all models are the same, and they aren't by any means the ONLY first tier vendor to consider.

    Have you run the cooling & heating load numbers for the upstairs (room by room)?

  7. GBA Editor
    Martin Holladay | | #7

    Q. "Won't the HRV or ERV with ducts still be noisy in the bedroom? even if we placed it in the limited attic space above?"

    A. A ducted HRV or ERV usually isn't installed in a bedroom. You will have a fresh air register, and the sound of the air leaving the resgister will be almost undetectable. Ventilation air flows are small.

    Q. "If I do decide to go with the HRV or ERV with dedicated duct work, can you suggest one that would serve only for upstairs? Or are they are all made for a full house?"

    A. Panasonic makes an ERV rated at 40 cfm, and there are other brands of ERV on the market. Many homeowners put their ERV or HRV on a timer, so that it operates (for example) for 20 minutes every hour.

    Q. "Also, regardless of the approach, getting an exhaust fan for the bathroom is a must, correct?"

    A. Yes. If you are unfamiliar with this topic, you should read "Bathroom Exhaust Fans."

    Q. "Regarding Lunos E2, would only 1 pair be enough for a bedroom space that is approximately 500 sq. ft.?"

    A. Yes -- I agree with Dana on this.

    Q. "Can these units be timed and only run during the day when no one is home? or start up in middle of the night when we are asleep?"

    A. I suppose any electrical device can be put on a timer if you want to. But in your bedroom, you want ventilation all night long.

    Q. "We only have 1 bedroom upstairs and 1 bathroom (total about 800 sq. ft.). So we originally thought only installing 1 ductless split unit for the whole upstairs (Mitsubishi I hear has good units). Do you suggest otherwise?"

    A. A single ductless minisplit would probably work fine, but it might be oversized for just one bedroom. As Dana pointed out, step one is always to perform a Manual J load calculation.

  8. eldarchik | | #8


    Thank you for the feedback, it seems Lunos E2s might be a simple option for me. Question regarding this:

    1. As per Martin's recommendation I'm still going to place a dedicated bathroom exhaust fan inside the bathroom (probably Whisper Green from Panasonic). So if I understood you correctly, I can place one end of the Lunos in the bathroom, while the other can be in the bedroom? if this is correct, can they be far apart from one another? Say 40 feet from each other? Or do they have to be near by?, the reason for this question is the bed then would be quiet far from the one in the bedroom and this might help minimize the noise, if it has to run all night long.

    What do you mean by first tier vendor regarding Split unit for Mitsubishi? Who else should I consider?

    Also, regarding split unit, as Martin mentioned that one split unit might be overkill for this room, therefore maybe I can purchase a split unit that has 1 outdoor unit and 2 indoor units and I can install the other one somewhere downstairs? Do you recommend to look for a unit that would have 2 indoor units or more? or are they not recommended and should have 1 outdoor to 1 indoor?

    And no, I have not yet completed a Manual J load calculation. Never did this before and need to figure this out. Is there an easy guide for this? Also, I'm only measuring conditioned space correct?


    I know the dedicated HRV would be an ideal solution, however to run duct work sounds like a lot of work at this time and we really not trying to do that, especially because only the 2nd floor has renovations.

    Regarding ERV, are you referring to the "WhisperComfort™ Spot ERV Ceiling Insert Ventilator"? If so, this seems to be a pretty cheap solution when comparing to Lunos E2s. $300 vs $1100. Are the Lunos E2s that much better than the Panasonic Spot ERV option? why would anyone install one vs the other? I guess I'm looking for some convincing points to narrow this down to Lunos E2 and pull the trigger.

    Thanks again for sticking with me on this.

  9. Expert Member
    Dana Dorsett | | #9

    The pair of Lunos I have in my basement are about 75' from each other (which is fine.) The power supply and switches get installed at one end, the other is only connected via low voltage wire (which can be of nearly arbitrary length.) You could even put one in the top floor bedroom, the other in the basement on the far corner of the house and it would still work, but the local ventilation on each half-pair would only be half the rated total (=11 cfm average, on high speed.) If there are two bedrooms that get used regularly you might just put one end in each bedroom rather than in the bathroom. No matter what you can't hit the 20cfm continuous flow in the bathroom unless you put both halves of the pair in there (which would be a waste).

    The tiny 1-room spot ERVs would be perfect for bathroom-sized rooms, but it's not clear how much mixing would go on in a 400 square foot room with those- the intake and exhaust are mere inches apart. With a Lunos pair it runs in one direction for 70 seconds, then reverses, running the other direction for 70 seconds. So each unit in the pair behaves as the exhaust port for one time period, supply port for the subsequent period, making it impossible short-circuit the air flows. At high speed it moves about 25 cubic feet of air on each cycle, with ample mixing time for the clean intake air to mix with the room air.

    A simple to use (but not super-accurate) online load calculator is When using it set the ventilation assumptions to "0 cfm", and the air tightness of the house to "very tight". If you're not sure what the R-value of any studwall or roof fluff is, guess to the high side, and it will probably be close. loadcalc doesn't have very nuanced shading factor inputs (unlike many professional tools), so if you have shade trees on the windows & roof for part of the day it won't give discount the peak cooling loads for those factors. It doesn't let you fully specify the SHGC or U-factor for the windows either.

    With all of that said, if you're a bit aggressive on the inputs it can give you numbers that are WAY better than a WAG, without the grotesque oversizing that seems to be standard in the HVAC installer-specified world.

    Multi-head ductless units have the issue that the heads don't modulate- they cycle on/off at their rated output, at whatever you set the blower speed to. It's more efficient and more comfortable if you can size the unit reasonable for the loads and use a single-zone modulating system that can ramp it's speed up and down with the load. With 800 square feet total, if the rooms are doored-off from one another, the loads of individual rooms are often below the minimum modulated output of even a half-ton mini-split, let alone a 3/4 tonner, but the total load for the whole floor can still be a large fraction thereof. In those cases a mini-ducted mini-split sized for the whole-floor load will usually be more efficient and more comfortable than multiple oversized heads cycling on/off.

    So, run the load numbers for each individual room and add them up. DO specify both the indoor & outdoor design temperatures used in the heating & cooling calculations too.

  10. GBA Editor
    Martin Holladay | | #10

    Q. "I have not yet completed a Manual J load calculation. Never did this before and need to figure this out. Is there an easy guide for this?"

    A. Here are some articles on the topic. If you don't want to do the calculations yourself, just read the first and last articles in this list:

    Saving Energy With Manual J and Manual D

    How to Perform a Heat-Loss Calculation — Part 1

    How to Perform a Heat-Loss Calculation — Part 2

    Calculating Cooling Loads

    Who Can Perform My Load Calculations?

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