In the lastest issue of Kitchen and Baths there is an article on range hoods that talks about the importance of makeup air. As I live in an R2000 house with gas appliances this is extremely important. However while mentioning the topic of makeup air, the Author does not tell one how to go about providing it. What is the answer, just crank open a kitchen window when you turn on the range hood?
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Hopefully someone with better HVAC experience will jump in.
Here is what I know... There are now make up air units that can be as simple as a dryer vent type of thing except that it allows air into the dwelling. Commonly it is hooked up to the furnace cold air return duct. From there the fresh air travels thru the furnace out into the room that is exhausting the air. If the building gets cold enough the furnace turns on.
When you turn on an exhausting appliance, vent fan for example, it allows air from outside the building to come inside.
Fancy versions of the make-up air unit have a thermal transfer wall that allows exhausted heat (furnace exhaust gas) to heat a common wall that preheats the incoming makeup air. The gases don't mix, but the heat transfers so that the incoming air is tempered.
If you have a fireplace there could be a make-up air duct there as well to compensate for the lost building air that travels up the flue.
So if I get what you and 4LORN1 are saying, the most effective way to ensure a positive pressure and keep things running smoothly when operating a range hood, is to pair it with some form of air intake system; an air to air heat exchanger would be effective and environmentally sound.
Obviously the two devices should be wired together and act as a single unit, with the intake on the air to air exchanger being slightly more than outtake of the range hood. For example, if the range hood is on a low setting and pulling say 150cfm of contaminated air, then the exchanger should be set to draw 175cfm of fresh air in. Similarily if the hood is on high and drawing 450cfm, then the exchanger would be set at 500cfm.
Does anyone know of any companies that sell systems of this type? It would be much easier to buy a 'ready-to-install' balanced system, than to try and create my own.
Thanks for your feedback.
Nick.
Tim described my make up air system with his comment:
"You can also provide makeup air/combustion air to the mechanical room/space with a gravity vent and a counter-balanced backdraft damper. "
There is no electrical connection in this setup. it just works based on negative pressure counter ballanced by a weight that keeps the occasional gust from blowing in the inlet.
As for the heat recovery unit I'd be critical of the internal components. The high efficiency furnace outputs are highly acidic. That is why they use PVC for the exhaust gasses. Plain galvanized steel would work - for a while- when it fails (rusts thru) we'll read about you in the paper as having died from Carbon Monoxide poisoning. The energy saved is not worth the risk in my opinion. Possibly the heat recovery units are safe & effective. I'd surely be cautious and have it inspected with your furnace on an annual basis.
Besides the exhaust issue, fresh air into the building is a good idea. It dilutes the bad stuff in your building. From Radon, to Formaldehide, to body odor, to mold & mildew, this make-up air system makes your building more breathable.
"As for the heat recovery unit I'd be critical of the internal components. The high efficiency furnace outputs are highly acidic. ..."
I think that you misunderstand the application of the HRV/ERV. No one is recommending use of a heat exchanger to recover lost energy in flue products.
An HRV/ERV can be used as an exhaust system, so long as we're talking about exhausting air. An by taking stale or damp or smelly air out of the space and introducing fresh outside air (OA) into the space, recover some of the heat (say in winter inside air is 70 - 75, while outside air is -15) and humidity before you dump it outside. The fresh, partially conditioned OA is ducted into the furnace return and mixed with other air and further conditioned by the furnace/AC before being supplied to the individual spaces.
BTW, residential construction is the only type where forced, controlled ventilation (i.e. outside air) is optional. All other types of buildings are required by code to meet minimum ventilation rates based on use and/or occupancy.
I saw a version of a heat recovery unit on this old House about 1 year ago. I think it was Tom Silva doing the installation. It wasn't a pointed interest at the time so I can't remember the exact details. It was quite an assembly and I am mistaken if it didn't use exhaust gases. I'm glad to hear it isn't common to use the exhaust gas to get waste heat.
As an add on to the message I do remember it was ungodly expensive to the tune of 400 bucks. That and having Mr. Silva cutting the tin probably created a really long wait for a break even on the energy saved.
Edited 11/19/2002 6:49:34 PM ET by Booch
Two comments on this discussion:
1. An HRV is a balanced ventilation system. Exhaust air volume is balanced by fresh air volume. An HRV is not inteded to be used as, and should not be used as, a makeup air unit.
2. A residential makeup air unit is sold by Shelter Supply, 17725 Juniper Path, Lakeville, MN 55044. 800-762-8399. 952-898-4500. Web site: http://www.sheltersupply.com
Martin Holladay
"An HRV is not intended to be used as, and should not be used as, a makeup air unit."
Why? Seems like a good use of it, if it's already in place...........
And it also seems like a good place to exhaust range hoods and such.
Not trying to be smart - Just curious.There is no difference between a wise man and a fool when they fall in love.
The need for a makeup air unit arises if a house is depressurized, as often happens when a range hood fan is operating. Operation of an HRV is "pressure neutral" -- it neither pressurizes nor depressurizes a house. If a house is starved for makeup air, you need a supply fan (a makeup air unit.) Turning on an HRV won't help a house that is starved for air, since the HRV blows out exactly as much air as it sucks in. If the house is starved for air, in needs a supply fan only, not a balanced system.
Martin Holladay
One other thing -- a range hood should never be connected to an HRV, which is not equipped to handle the grease. A range hood needs to be separately ducted from the HRV system.
" the HRV blows out exactly as much air as it sucks in."
I don't see how this is possible, unless they opposite sidees (intake/outflow) are built like an air compressor, where they move a fixed amount of air. I was under the impression they were just run by squirrel cage fans, so the amount of air they moved was variable. (And air could flow around the fans if they weren't running)
Good point about the range hood exhaust and grease - Hadn't thought about that.Love is the delusion that one woman differs from another.
Martin,
Good point, and I agree. You CAN balance an ERV any way you want to, within reason, but they are most efficient setup for equal flows. I also believe that as the house goes negative the ERV will provide more supply than exhaust, though not a good way to design.
In non-residential applications, I recommend and design using ERVs/ERUs as the exhaust fan for toilets, exercise room, locker/dressing rooms,janitor closets, and other areas that need GENERAL exhaust. In a house, that means bathrooms and basements (conditioned) only. Never have and never will try to use one as a KEF.
The makeup air unit from Shelter Suppy is an interesting product. I need to do some investigating into those.
Tim
I am facing a similar situation. We are installing a Viking 36" range hood with a 900 CFM roof-mount Viking blower. I knew it was going to seriously depressurize the house, so I installed a makeup air duct in the wall behind the range. It is 3-1/4" X 12" rectangular and exits directly behind the range. Where it emerges in the attic, it goes from rectangular to 8" round and then connects directly to a normally-closed 24 volt power damper. When the damper is open, the negative air pressure in the house caused by the range hood draws air directly from the attic and directs it at the back of the range, where I expect it will mix with the heat given off by whatever is cooking and not have too adverse an effect on the temperature in the kitchen.
The kitchen is pretty big. House is 3000 sf built in 1950 with all new high end wood windows and doors. It has been air sealed and, other than marginal dampers on the two fireplaces, it is about as tight as a 1950 house can get. We are in western Oregon, so I'm not too worried about arctic air being drawn in from the attic. When the clothes dryer is on, I don't smell the chimney.
My question is how to wire the damper so that it opens when the range hood fan is activated. Viking says that any modifications to the hood will void the warranty. Power to the roof mounted fan is controlled, of course, at the controls on the hood. There is a junction box at the top of the hood where the fan is hardwired with plain 14 guage 2 conductor romex. Obviously the speed of the fan is modulated by some sort of a speed control device behind the control panel of the hood. Will I mess this control up by wiring a 24 volt transformer in parallel with the fan motor?
I tried asking Viking directly but they were of no help.
Depending on the type of motor and how the control the speed there is a good chance that a transformer would work.But you can use a current sensing relay.Here is one sample.http://www.crmagnetics.com/newprod/ProductView.asp?ProdName=CR4395I think that Grangeir has current sensing relays.
Thanks for the reply.
After I posted this, I did some more research and found a much simpler/cheaper solution than that one. The skuttle A50 current sensing relay for sale at http://electronicaircleaners.com/ was only $20. A 24VAC stepdown transformer was another $22. The Honeywell ARD8 damper only draws .32A, so both the transformer and the relay have the amperage capacity to handle its draw.
I think I've got a real good solution now, and one that won't void my Viking warranty.
After I get it installed, I'll take some pictures and add a post about how things work.
BTW, your proposed system is pretty much what we installed in our home, with the exception that the makeup air was ducted into the main AC return instead of behind the stove. There, my HVAC contractor insisted on installing a DPST relay to turn on the strip heaters whenever the makeup air is too cold. I think I will disable that feature and see if we can live without it, because I fear what strip heaters can do to our electrical bill.
Another option might be to install a thermostate in series with the coils so that they only come on during the "coldest" weather.
Actually what you found is not only cheaper, but better for your application.The one that I listed was a universal (adjustable current, N.O. and N.C. contacts, time delay, etc) and I think that it needed power to operate.
I recently did another thread on makeup air. http://forums.taunton.com/tp-breaktime/messages?msg=71249.1
My BI insisted on the amount of MA to equal twice the outlet duct size. Sounds like your's is under that.
I also wonder WHY do you need a powered damper? I used gravity dampers in my set up. Powered ones sound like another place for something to fail.
A powered damper is required because if you have a damper on the one hand that allows air to come in,(make-up air) and another that allows air to exit,(exhaust fans and dryer vents) then you have a building that has flow through air leakage. If you don't have control over the envelope then you have no way to efficiently control the air in the building. You must control one or the other in order to have a tight building. It is easier to control the two makeup air sources in my home than it is to control the seven exhaust outlets.
Incoming I have make-up air for the hood and fresh air intake for the mechanical ventilation. On the exhaust side I have a hood exhaust, two dryer vents, and four bath vents. My house acheives an air tightness of .76 ACH50 or .038 air changes per hour under natural conditions.
I'm missing something.
The blowers themselves have vanes that act as dampers. Bath fans have a built in damper. These dampers act to allow air flow in one direction, but not the other. The gravity dampers I used only allow unidirectional air flow.
Doesn't your equipment have a similar thing?
Clarification--We're not talking about installing the power damper on the fan side, we're talking about installing it on the makeup air duct so that we have control over when unconditioned outside air is drawn into the building. I don't want the kitchen to get cold just because the bathroom fan or dryer is running or because someone opens a door on a windy day.
To filter out bugs, I am using a pair of the wife's nylons stretched over the end of the intake duct where it emerges into the attic. The attic is extremely well ventilated and full of cellulose, and I don't want dust drawn into the kitchen from the attic so that is why I went with something finer than window screen. I wonder if furnace filter media would work adequately and pass more air but still keep flies out? I have no idea and won't change it unless there is a problem.
I am glad to see some posts from others who have tackled this problem in a way similar to what we did. I could have gotten a lot closer to the 2:1 makeup air ratio if I had used two stud bays behind the range instead of just one, and then built a plenum above. That is actually a great idea. That would have been a massive duct and damper atop the plenum! Is a single unit sealed power damper even available in that size, or do you have to make your own damper and add a separate damper actuator? It was hard enough just finding the piece of ductwork required to go from 8" round to 3-1/4 X 12 rectangular. Better would have been 3-1/4 X 14 to 10" since the round duct is the choke point from a flow standpoint.
If the house was smaller and tighter or we had an indoor grill with the 1200 CFM Viking fan (biggest one they offer, also uses a 10" duct), OR we had a longer run on the makeup air duct, then I think I would have taken this to the next step and brought in a greater volume of conditioned air.
I will take photos as we go and post them up here. We'll see how it works the first time I cook blackened catfish or brew beer on a day when the fireplaces are going. It might not be perfect but I bet it will be adequate 99% of the time it is needed. For just over $100 in materials, it is sure to work a lot better than expecting the cook to crack a window.
A motorized damper for 10" round pipe is easy to find though you may have to order it in.
We install make-up air in all our houses due to the extremely tight nature of our construction technique. All our homes also have large hoods and most have ranges that include gas grills. My home is typical of our methods.
It has a 52" hood with a measured 1000 cfm output at high speed. We use variable speed controls on the exhaust and make-up fans. The exhaust side required 12" pipe and a 20x20 grill on the exterior. It was first installed with 10" pipe and we measured only 650 cfm of output. This was not enough to capture and contain all of the effluent during the grilling of fish or steaks or when frying bacon. I don't want to smell cooking odors in the house because that is an indication of particles in the air that will settle on furnishings and build up over time. Yes, even the wonderful smell of the turkey baking means turkey grease is getting on your furniture and artwork.
The make-up air is provided by a 10" pipe and is intended to give around 50% makeup at high speed. This helps insure that most of the make-up air goes right back up the hood instead of mixing with the room air. Commercial kitchens aim at 80% but use tempered air. We feel that this is cost prohibitive in a residential kitchen due to the small percentage of operation time. We screen the incoming air to remove insects and this screen needs to be cleaned annually depending on insect load. It gets pretty bad if you forget. The intake pipe must be insulated and wrapped with a vapor barrier to avoid condensation drips in the winter. The damper should be spring wound normally closed to avoid energy consumption when not in use.
The best place to introduce the makeup air is behind the range. The hood should be located as close to the range as possible. Ours is at 30" above the range. Regardless of what the manufacturers and the architects say, 36" above the hood is almost worthless and the amount aof air that you will have to move to acquire C&C is huge. Here is a link to a page that explains the different options in a 14 page version that is condensed down from a 100+ page report funded by the california energy commission.
http://www.jdpinc.com/pdf/designguide.pdf
To get adequate volume of air in a stud wall we often use a plenum above, that splits the air into three stud cavities. In the winter we recognize that some of the air will be cold enough to sink to the floor and not exit back through the hood. The kitchen tends to be warmer during these times and the only comfort issue is with cold bare feet. This is not an issue here in Texas as we have used the hood when it is 25 degrees outside without issue.
The optional path for the air is not preferable. Bringing in 1000 cfm of air through leaks in the building envelope will cause the perimeter of the home to be cold in the winter and hot in the summer. 1000 cfm is the equivelant of 2 1/5 tons of air conditioning. Our homes are so tight that you simply wouldn't get 1000 cfm without makeup air. There are a lot of issues surrounding this, such as fireplace use with hood operation with and without makeup air that there is just not space here to go into.
Make-up air is expensive to install. It is usually acceptable on smaller kitchens to open a window in the kitchen rather than spend the 1,000 to 4,000 dollars required to install it in even a reasonably adequate manner. Using a window for makeup air is simply not an option at the level of home we build.
The question will be asked, why build the home so tight? The answer is three fold. First, the energy consumption in my 4000 square foot home is 1000 KWh and 10 gallons of propane per month. This includes pumping and purifying our rainwater domestic water supply, circulating our hot water and several other luxury energy uses. Second is that our indoor air quality is superior to any other home that we have tested. Third is that we only have to dust 1/4 as often as we used to. We refuse to go back to building houses that leak to provide "fresh air".
Thanks for digging this discussion out of the archives. Perhaps enough time has passed that there are some new products people can suggest. I have read all I can on this subject (short of going to school to become an HVAC specialist) and still haven't found a good answer. I like your idea of exhausting a makeup air port behind the range. Can you show me a link to the 24 volt damper you are using. Does it come with an inverter to run on 120V? Does it look like that current sensing relay would work?I'm not sure that the oven or the range will really be that effective at tempering the air as it enters the room. The outside of ovens are well insulated enough that they don't get hot when the oven is on. My concern is that there would be a draft of cold outside air when standing in front of the range, making it uncomfortable in winter.I am interested in the earlier suggestion of letting a standard HRV setup sort out the pressure differences. Could you wire a the HRV fans to run when the vent hood is on? I understand that you don't want the vent hood to go THROUGH the HRV, but if they run at the same time, at least the air is tempered and you get fresh air into the house. I'm heating with radiant floors so I don't have the return plenum option that many people have mentioned. I have seen different answers as to whether you should vent the moist air from bathrooms through an HRV.Hopefully some of the HVAC gurus here can help us out.-Rich
I didn't want to pull cold air through the return air plenum. I don't want the expense of an HRV and I didn't want cold drafts coming into the entire house or hot air entering every room in the summer. We have A/C but it seems to me like the best place for that "off-temperature air" to emerge in the room is right behind the range.
Now I admit that some ranges are well enough insulated that you might just end up with a cold draft. But this is a six burner, 36" commercial style Viking range with a gas oven which exhausts its hot air directly up the back. It generates enough heat that I think it will work fine.
The "current sensing relay" should work fine. It activates on 4 amps and has more than enough capacity to handle the draw of a little appliance transformer, just the same as the one you already have inside your current furnace. A doorbell transformer would work just fine too.
The power damper we are using is the Honeywell ARD8. If I had the stud space to install an even bigger damper, I would, as I have read everywhere that a passive duct needs to be twice the diameter of the pressure duct (ours is 10"). Tell me how to install a 20" diameter passive duct, and I'm all over it!!
I am seeing, being an electrician, more make up air units. Most of these are just one way louvers. Some, the more efficient unit I am told, include a heat exchanger. More complicated make up air units, got to wire one the other day, have a blower controlled by a pressure sensor. Looked pretty simple to me. I don't know how they determine when they are needed or how they are sized but they sound like a good idea for a tight house.
I once saw a restaurant that didn't have make up air. The large exhaust unit over the grill would glued the doors shut if they, the doors, weren't used regularly. The thing that caused concern was the flame on the gas water heater blowing out or into the room, not up the stack. Being a real dive its burning down, assuming nobody was hurt, wouldn't have been a major loss.
I once saw a restaurant that didn't have make up air. The large exhaust unit over the grill would glued the doors shut if they, the doors, weren't used regularly. The thing that caused concern was the flame on the gas water heater blowing out or into the room, not up the stack.
Funny you should say that. I once worked in a steel fabrication plant office, with the fab shop attached, and the guys would start the exhaust fans (60", 5 hp, lots of them) without opening up any doors, 'cause it "would make it cold inside" during the winter (they had gas-fired radiant heat). There were no makeup air intakes. You couldn't open the office front doors when they did this, and one day the water heater insulation started to burn (inside a utility closet). We put in an electric replacement, although a makeup louver in the closet would probably have been fine, but it certainly got our attention.Be seeing you...
Nick,
"As I live in an R2000 house with gas appliances this is extremely important."
You'll have to explain this further. What is an R2000 house?
Also, it depends on the gas appliances whether or not this is important. Sealed combustion gas burners, like a high efficiency furnace are unaffected by building internal pressures. Direct vent appliances, those that take the combustion air from the space in which they are located are affected as are appliancees with gravity vents and fan induced vents.
"What is the answer, just crank open a kitchen window when you turn on the range hood?"
Depending on the weather, that not all that bad and idea. However, depending on how tight the building actually is, what other appliances are using indoor air, a good sized exhaust fan will cause the space to go negative in terms of relative pressure an suck air in through and path available.
In commercial kitchens, code requirements in most jurisdictions are fairly specific. Make up air must be provided for the kitchen exhaust hood (KEH) and it must be conditioned such that it is no less than 10 degrees below room temp. You can take credit for some transfer air from the adjacent spaces, but good practice limits that to no more than 20%. Many KEH's are "compensated" that is they have MU air ducted directly to them and disperse the air from the perimeter of the hood.
Greenheck, CaptiveAire, Larkin and others sell combination make-up/exhaust units for commercial kitchen exhaust hoods. No manufacturer that I know of makes a residential version.
The options are: to use an energy/heat recovery ventilator as the exhaust fan and makeup air unit; let it suck air throught the construction joints, windows, doors, etc (the better than average well insulated house leaks at a rate of 0.35 air changes per hour, which in a 3000 sf, 8' ceiling house = 140 cfm, most leak more); provide outside air to the house using a Skuttle (an automatic barometric damper) or similar device for all or part of the makeup, best done into the furnace/air handler return. You can also provide makeup air/combustion air to the mechanical room/space with a gravity vent and a counter-balanced backdraft damper.
The best advice is to consider these issues before you try to put commercial equipment in a house. If you put real restaurant grade equipment in, you have to put all of it in, including the ventilation system. The over-sized stainless residential monstrosities that are common today, are not commercial grade, though they need more than the average Broan noise maker will exhaust, they do not need much more. It is not practical to put a 1200 cfm kitchen exhaust fan in a house, without a competent designer attending to the details. In all practicality, a 400 - 450 cfm rated kitchen exhaust fan/hood will only move 350 or so (rating are typically at 0" static pressure, where actual duct, damper, hood and filter losses are on the order 0.5") and can be installed without serious consequence. IF, all bathroom exhaust fans were on, all direct vented gas burning appliances were operating, the house was extremely well sealed, and you had a high capacity KEH going and dryer venting out of the house as well, something would have to give.
Edited 11/19/2002 9:20:52 AM ET by Tim
Thanks Tim. Your last line sums up my problem. Even the article in the FHB K&B issue that prompted this letter was of no help in this regard. To my mind a publication of FHB's standing should be addressing indepth aspects of a topic, and leave the surface scratching to the coffee table rags.
Anyway, getting off topic! :o) In answer to your question an R2000 house is one that is well insulted and well sealed; the intent being to minimize heat lose (energy and money) through infiltration. Yes my appliances are direct vent units that do take the air right out of the basement space.
It would seem that this problem has been addressed in commercial applications, and I will have to look at the solutions you have mentioned. One must be able to come up with a domestic version.
Thanks for the info. Nick.
In southern Michigan most builders are using a Skuttle brand make up air dodad: (aka a "Self-Adjusting Make-Up Air Control"):
http://www.skuttle.com/216.html
Bob
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