A Solution for Fresh and Make-Up Air Happiness

A Solution for Fresh and Make-Up Air Happiness

Most of us are happy inside our homes, when the air we breath is fresh, and without the nastiness that can make us sick, or that is just plain stinky. As soon as it’s not fresh, we try to get rid of it. Some of us open a window or two. Others crank up an exhaust fan, in the kitchen or bathroom.

When it’s below freezing, or hot enough to melt pavement outside, either one of those strategies is cut short, or not used at all, because it makes us uncomfortable, which makes us unhappy. So, when we’re both comfy AND breathing fresh air, we tend to get really really happy, and happy people are good for the world. Sounds like an opportunity!!

A Solution for Fresh and Make-Up Air Happiness

Whether it’s because our home is tighter than tight, or there’s a need to neutralize the negative pressure in the home caused by turning on the range hood exhaust fan, bringing in outside air shouldn’t be done casually. By casually, I mean having a outside air inlet installed in the a floor or ceiling connected directly to conditioned space, where it can rush in on our heads or feet. I have it on good authority  a)From everyone I talk to  that that’s not happiness! You might disagree, but you also might be crazy.

So, the “opportunity” we have is to provide fresh and make-up air systems that not only do their job of bringing in outside air, but also keep us comfortable, healthy and, above all…HAPPY!!!

A Few Common Solutions

Many believe that an ERV  b)Energy or Enthalpy Recovery Ventilator  or HRV  c)Heat Recovery Ventilator  is absolutely the only way to bring fresh air in to a house. I say, in some cases, it’s a very good strategy. It depends! We have installed the ERV strategy before, and I’ve recommended it on dozens of homes, in the U.S. and abroad. We have proof that it works very well. The biggest “opportunity” (we don’t use the word “problem”, thanks to Dick Pritts, our mentor extraordinaire) with these systems, though, is justifying their cost when a very low cost system could be just as effective. For example, the ERV below was installed in this 2,811 square foot home, for just over $10,000, back in 2012.

A Solution for Fresh and Make-Up Air ERV Zehnder

Many also feel that bringing the make-up air in to the house as close to the range hood as possible is the best strategy. I agree that it is a very effective strategy. Plus, when you have ingenious ways of doing this, like our good friend Matt Risinger demonstrates it here, we’re loving it:

Did you notice that he said, “we don’t like these make up air dampers, because the bring air directly from the outside, in (where the happy people are), but we really need a way for that air to come in”.

Here’s a follow up video showing how it looks and operates, after install:

This may or may not work for you, but it certainly is one of the better solutions out there.

A Fresh Solution to Happiness

Here’s the strategy we like to use, no matter where the house is in the world, but it’s not necessarily appropriate for every home, and we wouldn’t think of recommending it as a one-size-fits-all strategy.  d)Please consult with professional with a special focus in building science and/or home performance

Here’s the gist of it: We use a semi-conditioned space, like an attic or basement area, to act as a large “buffer zone” for the incoming outside air. After the air enters one of these spaces through a filtered in-line fan (for fresh air) or filtered damper (for make-up air), it dissipates, and is “pre-conditioned” by the semi-conditioned air in the space, then it enters the home.

This pre-conditioned outside air then enters the conditioned space in one of two ways.

  • Through a transfer grille in a wall between semi-conditioned and conditioned space, that is strategically placed as close as possible the return grille of the air handler or furnace, where it is pulled in through the return grille, filtered again, conditioned properly, and distributed throughout the house via the ductwork.

A Solution for Fresh and Make-Up Air Happiness

  • When the air handler / furnace is in the semi-conditioned space, and the local jurisdiction allows that space to act as the plenum, like we did in the High Performance Bungalow, the incoming outside air can be picked up directly by the air handler / furnace in the semi-conditioned space to be filtered again, conditioned properly, and distributed throughout the house via the ductwork.

A Solution for Fresh and Make-Up Air Happiness

When I said it’s not for every home, I mean that homes with spaces like semi-conditioned attics and/or basements are the ideal candidates for this strategy. Rooms that are never or rarely occupied, but a part of conditioned space, like a laundry room, can also work well.

The details of each system / strategy can vary, but the goal is to create a “buffer” between the incoming air and the happy people inside, to keep them alive (fresh air) and happy (comfortable)

There are many many many many other considerations that someone who knows and specializes in Building Science and Home Performance best practices needs to review and help with. DO NOT TRY THIS ON YOUR OWN, without consulting with someone. Depending on the location, there may be high levels of humidity to manage, or the opposite, very dry air. Often times it’s both! So, get help!

FYI: Typical System Specs

FRESH AIR: Fantech FR-125 inline fan, with Fantech FB-Series Filter Box, controlled by Fantech switch in conditioned space.

MAKE-UP AIR: 10″ Broan barometric damper, with Fantech FB-Series Filter Box.



Footnotes   [ + ]

a. From everyone I talk to
b. Energy or Enthalpy Recovery Ventilator
c. Heat Recovery Ventilator
d. Please consult with professional with a special focus in building science and/or home performance

20 Responses so far.

  1. nate516 says:

    Gutsy post, Chris. Thanks for saying what needs to be said. We often recommend connecting an HRV/ERV to the existing duct system (we seldom do new homes). Sometimes a scuttle works well. It’s all about the house, the objectives, the budget, and the design.

    $10,000 in a new home can be put to far better use, and if it’s that expensive during construction, how about on an existing home, particularly a 2 story? $15K? 20K?

    Nate Adams
    Energy Smart Home Performance

  2. David Butler says:

    You can obviously get a good ERV/HRV installed for way less than $10k, but the real issue is that can’t use a recovery ventilator for make-up air. Recovery ventilators are balanced by design. Make-up air is 100% unbalance by definition. And if you were to try to route, say, 900 CFM cooktop exhaust through an HRV (assuming you could find one large enough), the hx core would quickly become unusable. Likewise if you try to filter all contaminants first. The filter would become a mainteinance nightmare and/or quickly become too restrictive. Maybe someone has designed a specialized HRV for commercial kitchens, but I doubt such a thing would be practicable for a home.

    I like your buffer zone idea. But the mechanical systems would still need to be sized to handle the additional sensible and latent loads within a reasonable period, depending on how isolated the buffer zone is from the house. Also, you have to consider how cold the buffer zone might get when its 0F outside. A 1200 CFM fan at 0F would create a 90k instantaneous heat load in the buffer zone. This is where judgement and house layout come heavily into play.

  3. We find the best method for make up air is the installation of an equivalent sized duct with an inline fan bringing the fresh air into the return plenum of the HVAC system servicing the same heat/cool zone of the Kitchen exhaust location. We have a pressure switch that compares the ambient exterior pressure to the interior pressure and kicks on the fan automatically. This switch activates(most often) during Kitchen cook top ventilation use and also when the dryer and bathroom fans are in use. The pressure switch can be wired to turn on the cooling or heating mode when it activates or -in a passive installation- the thermostat takes care of the problem once the set point is reached on the interior. Problem solved. The heat/cool system takes care of conditioning the air and the pressure differential is neutralized. Best of all the system is automatic and requires no activation on the part of the homeowner AND uses the existing heat/ cool system to temper the air.

  4. David Butler says:

    @Nordic, in low load homes (what Chris deals with), the make-up air for a commercial hood (600 to 1200 CFM) can easily create a load several times larger than the nominal design loads for the house (see my previous comment). It’s not uncommon for the homes we work on to require less than a ton for 1,500 or even 2,000 ft2. And when the outside dew point is in high 60’s or even low 70’s, the additional latent load will greatly exceed the equipment’s capacity.

    The buffer zone approach allows the load to be absorbed over time, thus a moderately oversized system can eventually recover without impacting comfort in the conditioned space. Note that even a perfectly sized system only needs to operate at full capacity during the coldest or hottest hours of the day.

  5. @DB There is no way to utilize an equipment capacity that is so modest in capacity relative to the square footage anywhere close to the numbers that you cite. Nor will the make-up air ventilation adequately be conditioned while running thru a buffer zone. In this case- if your structures are that tight- the only way to provide adequate make-up air would be to have a separate heat/cool appliance for that function alone. As has been observed herein HRV’s and ERV’s cannot provide make-up air as they are net neutral. They CAN however provide make-up oxygen -which can be meaningful if you have a fireplace running and don’t want to kill your clients. We get very few referrals from dead clients. :))

  6. David Butler says:

    Nordic wrote: “There is no way to utilize an equipment capacity that is so modest in capacity relative to the square footage anywhere close to the numbers that you cite.”

    Not sure what you mean. I’ve designed mechanical systems for hundreds of above-code and high performance homes (since 1999), nearly all having a capacity ratio in the range I cited. My clients span from northeastern Canada to the Bahamas to California.

    I see you’re in NY. A few years ago I specified 2-ton and 3-ton GSHP’s for a 7,000+ ft home in eastern Long Island. The load was less than 5 tons but the equipment didn’t come in half-ton increments.

    My last comment conflated the commercial range hood issue with the typical ventilation loads that Chris was referring to (which can be addressed with a buffer zone). My solution for that is to convince my clients they don’t need 1,200 or even 600 cfm for their large commercial style cooktops. A well-designed updraft hood that fully covers the cooktop can do the job with less than 300 CFM.

    But you’re correct that the only way to deal with the load imposed by 1,200 cfm exhaust is to reheat the MUA. The bigger challenge is the huge latent load that would impose in summer. I recently worked on a project in Grand Rapids where we went with chilled and hot water coils in series. The MUA system probably cost more than the range.

  7. What I intended was that if the equipment that you provide to heat and cool the house is that modest (2 to 3 tons for 7,000 sq. ft) due to the tightness of the structure- then you cannot use that air moving equipment to provide MUA even given an outdoor source- because the CFM in and CFM out are so mismatched.

    A 900 to 1200 CFM Vent fan can remove way more air than the heat/cool air handler can deliver given your systems relative sizing. We built a 9,500 SFt. house with a nine ton ground source system for the whole house and I thought that was an achievement. The numbers that you are citing are 25% of that @ 2 to 3 tons for 7,000 ft. These are numbers that are not common IMHO.
    A properly sized inline make up fan inserted into the return plenum with a pressure transducer is the way we have managed and it seems to work fine with the MUA. If it activates the Heat/cool cycle then no need for a buffer zone- if it does not activate the heat/cool cycle then the thermostat will take care of it anyhow. We have also used coordinated variable speed Vent hood/Inline fans to keep things balanced in and out.
    There’s a lot of ways to get to Hoboken I guess… Thanks for sharing.

  8. David Butler says:

    @Nordic: the main benefit of your strategy (feeding MUA directly into return plenum) is that MUA is distributed throughout the house rather than concentrated in one location. But it will only work when the ventilation load is “relatively small” compared to the house load.

    you wrote: “The numbers that you are citing are 25% of that @ 2 to 3 tons for 7,000 ft.”

    Sorry if I wasn’t clear. I specified a 2-ton *and* a 3-ton GSHP, for a total of 5 tons. I needed two air handlers due to the size of the house. In any case, that home barely met code. The town required a HERS Index of 50, IIRC. The only way that was going to happen was to install geo, even though it made no sense economically since they have access to inexpensive natural gas. Sigh.

  9. Bill says:

    Interesting discussion but thankfully the issue is not such a problem for a Habitat home. While we are designing & building very airtight homes, the small sizes (even our last 4 bdrm, 2 bath was only 1300 sq. ft.), we would not be putting in a huge range. In fact we are planning on an electric range option with PV on the roof next time. We use the small FanTech HRV with input air from the attic costing
    only a few hundred dollars.

  10. Gord Cooke says:

    Been there done all of this guys. A $10K HRV for a house is certainly a sham, there are 10’s of thousands installed in North America for under $1500. Moreover, we had this make-up air device that is being showed over 30 years ago and it was found to be more trouble than its worth. Trying to accommodate 2 functions with widely different air flow and timing requirements makes for a lot of control and ducting complexity. We have found best to let a small, effective HRV/ERV to do the continuous ventilation a separate dead simple make up air system such as Thermolec and Electro-Industries have so nicely designed is far simpler and cheaper to install and maintain

  11. Thanks, Gord. We’ve used and specified a variety of the ERV/HRV units, as well, including from the manufacturers you recommend. The one shown in this post was our first time using it, and mostly experimental for us. Getting it in to the project was made easy because it was a “media home”, so the cost was defrayed (OK, we didn’t pay for it). That’s not to say that it doesn’t work. In fact, quite the opposite. The ongoing monitoring continues to show us that it works way better than touted.

    Gord, you say, “…we had this make-up air device being showed over 30 years ago…Trying to accommodate 2 functions with widely different air flow and timing requirements makes for a lot of control and ducting complexity.” If you are referring to scenario that we’re showing and suggesting in this post (not the ERV), I will clarify the way it’s set up:

    The two functions (fresh air and make-up air) are absolutely separate. The inline fan is providing the fresh air through a 4″ duct in to the attic more than 10 feet away from the 10″ barometric damper that is providing make-up air for the range hood through a 8″ duct (10″ damper was the only available size at the time, according to installer)? Ducting for both is no more than 12″ long from roof-line to filter box, and filter to each device. The controls for the inline fan is stand alone, in the pantry, well marked with instructions for the owner on proper operation. The damper has passive controls, nothing wired. The weight on the damper lever is set and verified to allow the the damper to open only as much as is necessary to provide the desired CFM of the Range Hood, so that when it’s calling for 350, and there are no other openings to let in fresh air, the damper opens enough to meet the 350. When a window or door is open, and there’s enough air coming in through that opening to allow the fan to operate at 350 cfm (or whatever it’s calling for), the damper stays closed. Does this make sense?

    Whether this is what you meant or not, it may be good for others reading this to have a bit more explanation about how it works. Either way, it be good to hear back. It’s a very simple set up. We also considered an ERV, but while the investment would have been minimal relative to the total cost, the owner (on our advice) decided to put that same money in to our even lower cost system, the building enclosure, and, yes, maybe a nicer butcher block counter top :-).

    The set up is working VERY well. VOC and RH sensors in the attic and throughout the house, as well as energy consumption monitoring, is showing that this system is working very effectively, and using very very very little energy, and contributing very little to the heating/cooling loads. Oh, and it’s almost silent 🙂 We’ve also been keeping a close eye on the H2 sensor (“Happy Homeowner”), and the readings are always maxed out at “Extremely”.

  12. Thanks, David. As I’m sure you are, we’re asked to connect range hood exhaust to ERV/HRVs on every project we’re involved with, whether we’re designing it, building it, or consulting on it. The answer every time is, “NO. Period.” When we’re asked to specify and/or install a BIG range hood, that’s at LEAST 1,200 CFM, our answer is, “NO. Period.

    We generally stick to the calculation that Armin Rudd suggests in his “Ventilation Guide“: 150 CFM per linear foot of cooktop surface for gas ranges, and 100 CFM per linear foot for electric ranges. Finding small enough range hoods to meet this requirement is becoming easier, as manufacturers are making more of them. For this house, we found a hood with a 400 CFM max capacity.

    As a side: The one thing we are STILL having difficulty with is finding a hood that’s deep or wide enough to extend at least 1″ to 2″ past the edge of the cooktop for a more effective capture. The deepest I’ve seen is 26” overall. It works pretty well, but custom is the only way to get it close to the way I’d prefer for effectiveness. Custom isn’t always in the budget…

    Even more difficult, is finding a range hood that actually is 100% effective at removing all contaminants produced from cooking, and that is 100% attractive. As of yet, it’s impossible, but working on it!

  13. @CLG As you correctly note the HRV and MUA functions are separate and the need for each can have different triggers.
    When you have a passive barometric damper bringing in MUA that’s fine -but how do you condition that air?

    Last night in our neighborhood it was minus 5 Farenheit. The attic as a tempering space will not serve for pre-heating. I ‘m not sure your technique would be acceptable to our clients-in our climate zone.

  14. David Butler says:

    CLG wrote: “We generally stick to the calculation that Armin Rudd suggests in his “Ventilation Guide“: 150 CFM per linear foot of cooktop surface for gas ranges…”

    For a standard 30″ gas range, that works out to 375 cfm. That’s almost double the 200 cfm rate recommended by Brett Singer for a standard size range (re: his presentation at 2013 Building America Technical Meeting).

    Without seeing the context, I’ll withhold judgement on Armin’s guideline, but it seems overly conservative. That’s fine if you’re only concerned with exhaust, but in a low load home, the MUA issue looms larger, thus the need to pay attention to hood design, as you noted.

    Recall the main point of Brett’s presentation was the huge variation he found in range hood capture efficiency. A 400 cfm hood with 30% capture efficiency isn’t going to do nearly as good a job removing NO2 and CO as a 200 cfm hood with 80% efficiency. (There’s no such thing as 100% efficiency.)

    Although there’s currently no rating system for hood efficiency (I believe Brett and others are working on that), we should pay heed to his advice to specify hoods that fully cover the cooktop, and are not mounted higher than necessary. It was obvious from his research that these criteria alone accounted for the lion’s share of the variation he found. As you noted, it’s hard to find full coverage hoods. However, that’s mostly an issue for pricey commercial ranges that measure 36″ and even 48″ wide. In that case, the cost of a custom hood looks pretty attractive compared to the cost of a MUA system with chilled water and reheat coils.

    As I noted in a previous comment, I believe a well designed 300-cfm updraft hood (e.g., full coverage of cooktop, mounted reasonably close to the burners) should be adequate for all but the largest commercial range in a residential setting.

  15. Bo says:

    I have been looking into these for awhile but have never seen one nor know anyone that has installed one. I thought I would share to see what you guys think:


  16. David, I’d agree that there’s no such thing as 100% capture efficiency in an off the shelf residential range hood, but 100% capture efficiency IS possible. ASHRAE Journal November 2015 had a good article on design considerations for commercial kitchen range hoods. The concepts there can be applied to residential hood design.

  17. David Butler says:

    @John, thanks for the tip. It’s on my desk, along with December, January and February issues =:-o

  18. @Nordic: In the house example shown in the post, we installed the ducted mini-split air handler, which is constantly running, in the same encapsulated attic area as, and near the fresh air and make-up air outlets. The return side of that air handler has a filter, and is left open directly to the attic. During heating and cooling seasons, when the make-up damper opens or the fresh air fan is running, the air handler picks most of it up right away, filters it (again), conditions it, and then distributes it.

    Since the outside air must come in to the house regardless, to provide the make-up and fresh air, this buffer zone (attic) can be a better alternative than in to conditioned space. If the attic is not an option, because it’s not encapsulated, or the code doesn’t allow using it as a plenum, than having the outside air outlets as close to the return grilles as possible works very well, as long as it’s a VRF (aka mini-split) air handler that runs constantly. If it’s not VRF, than having the return grille and outside air outlet in a part of the house that won’t cause discomfort becomes an “opportunity” to get creative.

    Make sense?

  19. Thomas Knotts says:

    Bringing in raw, unconditioned air into a house is asking for trouble, especially here in the south. We have wet conditions in the winter, and humidity in the summer. Both are potential conditions for an imbalance to the conditioning of the rest of the house, and not to mention inviting the potential for growing mold. The air must be conditioned. Connecting to the HVAC system is a bad idea also. Conventional residential HVAC systems are not designed to handle large amounts of unconditioned air. Some contractors then decide to increase the tonnage to account for the extra air. Bad idea! What happens when you oversize a system? Short cycle. The system would need to condition the extra air, for the hood, ONLY when the hood is running. What’s that… maybe 30 minutes? The rest of the time the system would be too large for the house. The hoods are a bad idea for any house. Personally, I cannot come up with a scenario when such a large hood his needed in a house. Sure, they look good, but do you really need that much ventilation air? This is delving into a commercial application, with a TRUE makeup air system, which provides conditioned air into the space.

  20. […] much and how well fresh air is being brought in to, and unwanted air is being evacuated (i.e. exhausted) from the occupied spaces inside the […]

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