I'd be concerned about any contractor suggesting your installation doesn't need to meet code requirements. In this case, they're making assumptions about the air infiltration rate in your home. At some point, your home might have had an insulation retrofit that qualifies it as "tight" even though it's got some age on it. They wouldn't know that.

Assuming your state's building code doesn't alter the relevant portion of the International Residential Code, you need to provide make up air for any range hood over 400 cubic feet per minute (cfm) in capacity. If your range hood is 800 cfm maximum capacity, then you'd need to make up 400 cfm. That assumes the other 400 cfm is made up by the leakage rate, which isn't true for all homes (it wouldn't be a good assumption for a "tight" home.)

There are a number of pre-engineered make-up air systems such as Fantech's MUAS. You can add a duct heater if needed. The cost of the equipment only should run around $1,500 plus tax and freight for the MUAS 750 and around $800 plus tax and freight for a duct heater.

I don't have time at the moment to repeat the main points, but pending getting back to you please review the two recent [last few years] Appliance Forum threads with "hood FAQ" in the titles, search for other MUA threads, and also see https://bamasotan.us/range-exhaust-hood-faq/ for MUA and indoor air quality related information.

I will note that standard approaches are often thwarted by existing house architecture, so ideas from these various threads may suggest a scheme that is compatible both with your house and with MUA requirements. Also search on "combustion appliance."

Hi Charles! Thank you for your response! It was my concern as well when appliance providers said we didn’t need it-I figured they are the experts on appliances, but an HVAC tech would be my go to for expertise on make-up air! The HVAC provider I spoke to admittedly said this was not his area of expertise. I can’t seem to find one that is. He suggested a range hood that has the duct for the MUA in it as another solution. Do you happen to have any knowledge on that? Also, the system you suggested-is it difficult to install? What you’ve mentioned seems like a much more cost-effective solution so just wondering the tech got his $8k figure from.

Our home has had no blown insulation but does have new windows-it is a drafty farmhouse but I am concerned nonetheless and want to make sure I’m doing right by my family and keep our house safe as can be with this new appliance. Some have suggested just opening a window, but does this really do enough?

Thank you in advance for your time and expertise

Hi Kaseki! Thank you for the direction! I’ve been scouring all of your posts for the last few days trying to understand more. I will certainly look into these and would love all additional feedback you can give as I realize each home requires it’s own solution due to multiple variables!

Your appliance provider isn't the one who might incur the wrath of the local code official nor the one putting their reputation and their license at risk.

Opening a window will provide make up air, but it's not an option in the prescriptive code.

Installation of one of the packaged systems for make-up air is pretty straightforward, but every home has its unique challenges. You'll need a competent mechanical contractor and electrician. Finding the former is likely to prove more difficult than the latter.

Some quick thoughts...

- Even in a very leaky house proper MUA is important. Without it you can be sucking air in through openings in wall cavities which creates a number of problems. One is that whatever is in the wall cavity (mold, mouse turds, etc.) gets sucked in to your house. A bigger problem though is if air outside is humid then this humidity gets pulled in to your wall cavities and results in mold. Not to mention discomfort from cold drafts.

- $8k seems exhorbitant. An Electro EM-ME10-240-1-14 (900 CFM x 10kW) is about $2200. It'd take a lot of very difficult duct work and electrical to eat up another $6k for installation. Not impossible, especially in an older house, but not probable.

Thank you, Opane! I agree, I’ve now called 7 different HVAC companies in CT however and none (aside from the one for $8k who admittedly also said he doesn’t do this work) has ever heard of/done make up air for range hoods. Do you have any recommendations for what kind of company to call to install your aforementioned solution?

Although we haven't gone over the hood system yet for requirements so we can get to the MUA requirements, if you have a place for a device such as the Electro, or some similar device from Fantech, then with some factoids provided by us you could get a HVAC guy to duct it.

There are commercial hoods that are designed to operate with roof mounted upblast blowers and roof mounted MUA conditioners that are somewhat proximate. The MUA is brought down to the hood via a parallel duct and either further ducted to the base of the cooking device at the floor (note commercial stuff has legs), or ducted to a wide diffuser at the ceiling attached to the hood and directed away from the cooking device. The goal is to replace the cooking plume air and not induce turbulence into it.

For more information and to fill out your reading list, the first dozen pages of this reference will be helpful.

https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

Kaseki, thank you so so much for all of these helpful links. I have been reading all that you recommend but I have to admit it’s somewhat over my head. We were hoping that we’d be able to have an in-line blower with the stove mounted against an external facing wall and and do one 90 degree turn in the hood vent to the outside. From what I’ve seen in the literature you provided, I’m not sure if roof mounted MUA/hood vent will work for us due to no space in the walls for ductwork (we just put up brand new sheet rock across the entire kitchen wall). Would the electrofan/fantech devices be a bit more feasible for an older home as it would live in the basement and ductwork could simply tie into the return for the furnace? Forgive me if I sound ignorant on this subject-I’m trying to learn from the ground up on it, especially since no contractors have been able to give me a straight answer.

Sorry that you didn't get to this before finishing the kitchen wall. The hood can go directly outside, or a tad up and outside. In either case, you most likely will need either an in-hood blower or an external blower. Room for an in-line blower seems to not exist, given your description, but perhaps it could perform a 90-degree duct directional change if inside a cabinet.

I was not suggesting the commercial approach of a large blower and MUA assembly on the roof, only explaining what combo systems might be configured as.

Treating the MUA as a separate system, you need some volume to hold the filter, blower, and heater, and a means of ducting air to it from outside to inside, and from it to the kitchen. Some shortcuts may be possible.

First, do you have any combustion appliances that take air from any space connected (air-wise) to the kitchen? What are they?

Second, do you have a fireplace you hope to operate while running the hood that takes air from the inside house volume?

Depending upon the answers the nature of the MUA complexity may become firmer.

Note that I don't know the limitations of MUA inserted into furnace ducting. I seem to recall that Fantech objected to that approach for another forum member here. Opaone will need to expound on that.

I've used the Fantech MUAS (without a duct heater) for range hood make up air applications. Fantech recommends that "make up air be ducted to the space from where the compensated exhaust is being removed." So, if the compensated exhaust is a range or cooktop vent hood, the make up air should be delivered to the kitchen.

There are a variety of issues with introducing make up air into the return air side of an HVAC system, most of which are related to the temperature difference between the make up air and the desired indoor air temperature and the required make up air flow rate.

Thank you for the follow-up, Kaseki and Charles and for clarifying both of those points!

To answer your questions:

1. we do have an oil burning hot air furnace and in the dining room we also have a pellet stove that we would run in the winter ( it is an open concept to kitchen space)

2)We do have a wood burning fireplace that I imagine at some point we would like to run at the same time as the range.

Charles Ross Homes-have you installed these units in homes with colder climates like CT and does it create any issues not having it heated?

Thank you both for your help!

Heating the MUA is just a wiring issue, and maybe an electrical service issue. The problem is that the pressure difference between outside and inside that induces back-drafting of combustion appliances and fireplaces can be very small, and the house pressure drop with the hood system on high can be significant. This means that the MUA system needs some control of its blower to assure that house pressure closely tracks exterior pressure.

Thank you, Kaseki! I’ve been reading your past posts-would you mind sharing again what cooking device/range hood/ makeup air system you chose and why?

@Alaur87,

I'm glad to report that I have no absolutely no experience installing make up air (MUA) units in cold climates and don't intend to gain any. I have, however, installed dozens in our (mixed-humid) coastal VA climate.

To be sure, heating make up air is not an engineering challenge. Duct heaters are simple, easy to control, and inexpensive devices--at least with respect to initial cost. We find that we don't need them for MUA systems in our climate zone. The concern is if outside MUA were to be introduced into the return side of an HVAC system when cooling is required--as it is for roughly eight months of the year in our climate zone. In that case, the HVAC system needs to be able to condition and move both the volumetric flowrate of MUA in addition to the normal flow rate of air recycled in the home for comfort. That could result in some seriously oversized equipment for normal conditions (i.e., when no MUA is required) or significantly reduced comfort levels. It could also result in condensation in return ductwork without special attention. We avoid both by introducing the MUA in the kitchen in proximity to the range hood--but not so close as to interfere with the flow pattern in the hood. A supply grill above the wall cabinets or in the ceiling are two options we've found to work well.

If a MUA system is designed to deal with smaller volume exhausts such as bath vent fans, clothes dryers, etc. and not a high volume exhaust like a range hood, introducing the MUA into the return side of the HVAC is less of a concern.

The potential for backdrafting of appliances is always a concern. It can be reduced by specifying sealed combustion devices (e.g., hot water heaters and furnaces) and/or locating them outside the conditioned space--such as in a garage. We install mostly manufactured fireplaces which have glass doors and outside air ducted to them so potential backdrafting is reduced for those sources as well.

Thank you, @Charles Ross Homes, @kaseki and @opaone for all of your input and help. I've run into a bit of a dead-end here. The one HVAC provider who said he would provide me with a quote for a commercial hood range/MUA all in one system has now said he "can't find anything that would work" and has stated instead that he thinks the "best solution" is to buy the damper from Wolf Appliances (I was considering going with their range hood) and he will write-up a quote for ducting it into our furnace return. I have to admit I am completely at a loss as to what to do or if I should even proceed with this route as the owner of the company did say that this "wasn't something that they do". Will this solution be enough??

I have now called 14 HVAC providers, 3 appliance stores, our town's building department and 3 kitchen design companies and NO ONE has any info on to who to turn to to install an MUA or to even get a quote. I feel completely at a loss as to where to turn to.

CR Homes, aren't HRVs and or ERVs required by code in some areas, and can't they serve as the portals for make up air? If so, maybe the HVAC contractors who use more current techniques and equipment will gain familiarity while the dinosaurs stuck with same old things, the same old way will be left behind.

If not, then, okay! ;-)

"Thank you, Kaseki! I’ve been reading your past posts-would you mind sharing again what cooking device/range hood/ makeup air system you chose and why?"

You may find images of elements of my kitchen in various posts. I won't repeat them here. Also, some hood flow parameters may be found in FAQ I. Please note that my kitchen reno planning began in 2007, with most purchases of appliances made at the end of that year. Delivery was taken significantly later for most items, but well in time to confirm measurements and interface details. Explaining rationale would make this tediously long, take too much of my time, and jack this thread. I owe a kitchen photo to the FAQ II thread, and one or more should appear in the fullness of time.

The cooktop: I have two induction cooktops, a 36-inch Frigidaire Gallery (replacing a 36-inch Electrolux clone Kenmore that failed after 5 years or so) and a Cooktek 3500W induction wok. These are set in soapstone over cabinets in which there is added stone support and wire racks for pans, providing maximum air volume for cooling.

The hood system: Overspreading these is Wolf's largest Pro Island hood set at 34.5 inches above the counter. The hood connects to a damper, then a Fantech silencer, and then a Wolf (Broan) 1500 CFM roof blower (which has a damper). (As I have explained many times, once installed in a hood system blowers cannot flow their rated CFM due to pressure losses. I have measured, however, about 1000 CFM with presently passive MUA and no other household exhaust blowers operating.) Duct is 10-inch.

The secondary hood system: There is a secondary system comprising a pair of ceiling registers (14 x 20 if I recall), 3M Filtrite filters in the register boxes, a damper, silencer, and roof mounted NuTone down-blast blower. I believe this blower is rated 600 CFM, but can't find my literature for it as it was originally bought to provide additional flow for a '70s cooking center with miniscule blower performance. The registers are ceiling mounted over a pair of Wolf wall ovens.

The MUA: I have planned an active MUA system, but all parts have not yet been acquired. There seems to be no end to new "required" projects. The system as it presently exists is operated passive, and comprises a highly ventilated attic with an additional roof-mounted down-blast commercial blower housing for eventual ducted air intake, a one-inch pleat 24 x 24 furnace filter (to be replaced with a lower pressure loss 4-inch pleated canister version, a 30 x 30 heat exchanger connected to my oil-fired hydronic heating system, and a 36 x 36 diffuser at the end of a hall that connects to the kitchen.

The control system for this is intended to keep the kitchen pressure equal to the outdoor pressure (which will be the attic pressure once the MUA is ducted). Some elements of this are place. A Fuji computer module in a DIN control array next to my furnace will attempt to adjust its natural frequencies (poles and zeros) such as to make a stable MUA system independent of the main hood flow rate, the wall oven vent flow rate, and bathroom blower flow rates. The differential pressure sensor upstream and motor downstream control loops are 20 mA current type. Separate sensors and controls are used to keep the heat exchanger from freezing when not in use and otherwise keeping the air passing it temperate.

Blower will be the largest that can get into the attic that Fantech sells that incorporates the 10 Vdc control voltage motor. (I forget the part number.) This wasn't available back ca. 2010, nor did Fantech list a motor controller that could handle that size motor back then.

If starting from scratch, I would investigate the present offerings of Electro and Fantech to minimize my work, but large flow rate in an assembled unit would likely not fit into the attic without removing the diffuser and heat exchanger for a one-time installation.

While balanced air pressure is highly desirable for several reasons repeated often on this forum, I should note that my System 2000 oil furnace has its own MUA and a sealed exhaust stack installed within the original brick chimney that served the previous one- and two-generations-back Beckett boilers. The hot water storage is heated via a hydronic loop on the furnace, and the dryer is electric. Hence, back-drafting of combustion appliances is not an issue.

To deal with the flow to the MUA heat exchanger (capable of 120k BTUh if necessary) as well as the longer reaches of my house hydronic plumbing, I use a larger (higher head vs. flow rate) Taco pump than is usual.

@Elmer J Fudd,

Indoor air quality (IAQ) is an area where the building codes have lagged building science by a number of years. For some time, the International Residential Code (IRC) has prescribed the ventilation requirements for attics and crawl spaces, but not living spaces.

Some states look to ASHRAE standard 62.2 as a guide for living space ventilation requirements. I believe your home state of California has integrated the requirements of ASHRAE 62.2 into the statewide building code. The requirements include a ventilation rate of 0.35 air changes per hour (ACH) but not less than 15 cubic feet per minute (cfm) per person.

The IRC doesn't require a vent hood to be installed for a cooktop or range in a living space even though it is well established that cooking is a point source for moisture generation, and, for gas-fired appliances, that products of combustion can be introduced into the living space. That said, if you elect to install a vent hood, the code prescribes the make-up air required if the exhaust rate of the hood exceeds 400 cfm.

Heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs) are balanced ventilation devices; i.e., their intake and exhaust flow rates are equal. Accordingly, they don't produce nor count toward the required flow rate for make-up air.

The OP would be well served to install a plug-and-play type make up air system. I would recommend the system introduce make-up air in proximity to the range hood and not into the return side of the air handler.

ERVs/HRV's encounter a few problems in trying to be MUA. They have much lower airflow rates, often less than 200 CFM while MUA's are typically 400-1200 (or more). Any conditioning of incoming air is via entropy from exhausting air while MUA's often need and have heating capability built in (this can and sometimes is done downstream of the MUA blower though).

As an energy saving measure our ERV's do not run any time an MUA is running as doing so would be redundant but that's about the extent that I think there can be any interaction between them.

For Plug & Play I recommend Electro Industries. Their systems work well and have the intelligence needed to operate properly.

One benefit of pushing MUA in to the return is that the house HVAC system can heat/cool/dehumidify/humidify the incoming air and for this reason it is common to do it and that's what we did. Ideally though it should be supplied directlly to where it's most appropriate (typically on the opposite side of the kitchen from the range) but this may require extra conditioning.

@kaseki, me thinks your post is the beginning of an addition to the FAQ about various systems that work and would be recommended.

HRVs temper incoming air via simple air-to-air heat exchange with exhaust air (i.e., sensible heat;) ERVs have an enthalpic core which allows for some moisture transfer (i.e., latent heat) as well. Let's keep entropy bottled up where it belongs (hey, I just made up a thermodynamics joke.)

The problems with introducing make-up air (MUA) into the return side of a HVAC system are, well, manifold: 1.) The system needs to be sized to heat and/or cool the MUA flowrate in addition to the normal HVAC flowrate in the home; 2.) It needs to be able to distribute the additional MUA flowrate throughout the home; 3.) It needs to respond quickly to changes in demand or risk compromising occupant comfort, and 4.) It needs the turndown capability to control reliably at conditions when MUA is not required.

To consider the implications, let's look at some numbers. Let's say a home has a zoned HVAC system with the 1st floor air conditioning system rated at 4 tons. As a rule of thumb, the air flow for conditioning the home would run around 400 to 500 cfm per ton or 1,600 cfm to 2,000 cfm for this example. If the home has a commercial cooktop or range that requires 800 cfm of MUA, and we duct it to the return side of the HVAC system, we need it to be able to distribute the additional 800 cfm in make-up mode. That's either 800/1,600 or 800/2,000 which is a 50% or 40% increase in the air handler's flowrate, respectively. So we now need to push either 50% or 40% more air through the 1st floor ductwork system in order that 800 cfm can eventually find its way to the range hood where it will be exhausted. And, unless it's Julia Child's home, we might need that additional capacity for about one hour a day-- which is less than 5% of the time. That's a lot of blower capacity to have in reserve for 5% of the time-- not to mention the implications for the duct work.

The majority of air processed by a residential HVAC system is recycled; the rest is leakage air plus any air supplied by a fresh air ventilation system like an HRV or ERV if there is one. If the thermostat has, say, a 2 degree F differential, the example system might be cooling 1,600 cfm to 2,000 cfm of 72F air to 70 F or heating 1,600 cfm of 68F air to 70F. If 800 cfm of make-up air is ducted to that same system, it has to heat or cool (and dehumidify) it, too. And that 800 cfm make-up air flow isn't at indoor conditions--it's at whatever outdoor conditions are. That means in the winter we've added significant heating demand and in the summer, significant cooling demand. A duct heater can easily fix the heating issue, but I can't imagine adding a 800 cfm continuous cooling and dehumidification load when the air is supplied to the system at 95F and 90% relative humidity, which is to say, I'm not doing the calculations, but it's a big increase in demand. It will require the equipment to be upsized, big time. Again, it's for roughly 5% of the time. Most HVAC system have limited turndown capability without MUA. The big hunkin' system needed for 5% of the time needs to be able to control to design conditions the other 95% of the time at a much, much lower load. That's a tall order.

I'm an advocate of fresh air make-up systems to improve indoor air quality and I believe that make-up air should be supplied for high-capacity exhaust systems (plus the code requires it.) I just don't think it makes economic sense to combine the systems unless the climate is mild with respect to both temperature and relative humidity. If not, I believe the more practical and economic solution is to install separate systems appropriately sized for the respective applications. I also think it's a more elegant solution to deliver MUA in close proximity to the use point (i.e., the range hood) without first taking it on a tour of your home and without paying for any conditioning other than filtration.

Charles Ross Homes- thank you for the post above!! This whole thread is enlightening as we need to install hood and our county in MD mandates MUA. I am going to go for separate system for MUA and need to now find a contractor to do this work.

Thank you OP for starting this thread!!

I would only add to @Charles Ross Homes submission above that because the MUA should reach the residential-style hood as free of turbulence as practical, which means from across the room at a minimum, it will need to be heated in cold climates. Cooling may be unneeded for many (he says from NH), or at least the warm breeze may be tolerated in the kitchen. Indeed, insufficient cooling could be an issue if the MUA is distributed throughout the residence, as noted among the manifold good points made above.

In commercial kitchens where MUA cooling is not provided, only heating in very cold weather, dumping the MUA into the volumes under the cooking appliances (which are usually on legs) has been deemed practical, but there is turbulence with this scheme, and it requires the large entry aperture of the commercial hood as well as adequate air flow to compensate. In restaurants where some MUA is injected into the customer area to keep down kitchen odor, that portion needs to be fully air conditioned.

As may be evident to many, in residential applications MUA system design and integration is usually more complex than the hood system.

It is very clear to me from my research that Make-up air is appropriate for anything over a 400cfm... and still desireable at 300cfm.

As for heating cold outside cold air, the fantech Muah 10/10 can handle a 79 degree increase from outside air at 400CFM, a 63 degree increase at 500cfm and a 53 degree increase at 600 CFM. Fan. that's all the reseach I've done as I only need up to 600 CFM, but I can see it will be challenging to get all the warming one might want with 1000+ cfm hoods. Fantech does provide this information upon request.

What I can't find is a competent HVAC installer who will do the installation for me.

Anyone know an HAVC company that could handle installation of this system in upstate NY?

please email me a rdg.gtp@gmail.com if you can help. Thanks very much!

Robert

You do not need a makeup air unit period all you have to do is put a 12 to 14 inch ducked from outside into your plentum of the furnace.

What if it's not "duck" season? Can you legally install such a system if it's not duck season?

Whether a passive (no blower) MUA can be used, even with a window sized duct, depends on the pressure losses of the duct path vs. the back-drafting sensitivity of combustion appliances. Any filter on the passive duct, even a screen, will cause a pressure loss. And sensitivity may be appreciated by these data provided by another forum member (name lost to history).

Mechanical-Draft Appliances

Heating systems with fan-powered exhaust systems can withstand higher negative pressures than natural-draft appliances. Some types of fan-powered systems are much better than others, however. In order of effectiveness, the choices are:

* Sealed-combustion. Also called “direct vent,” these appliances draw all combustion and dilution air from outside. These can typically tolerate negative pressures in the range from 25 to 50 Pa.

* Power-vented. These draw their makeup air from indoors and are also called fan-assisted, forced-draft, or mechanical-draft. These can typically tolerate up to 15 to 20 Pa of negative pressure.

* Induced-draft. These have a small fan added for energy performance, not to overcome house depressurization. These can typically tolerate 5 to 15 Pa of negative pressure.

By comparison, an atmospherically vented furnace can back-draft with as little as 5 Pa of negative pressure, and a gas water heater will have spillage at 2 or 3 Pa. Fireplaces can start having problems at about 3 Pa. Canadian codes limit negative pressures in homes with atmospherically vented equipment to 5 Pa. U.S. codes do not currently address the issue (in a plainly spelled out "prescriptive" number).

1 pascal = 0.00402 inches, water column

1 atmosphere = 407 inches, w.c.