Litawyn
New Member
Posts:46
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| 30 Jan 2012 01:31 AM |
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I need some guidance from the experts on here. I'm soon to be building a new home here in Maine where energy efficiency is a top priority. The house will be small (1,200 sq ft), heavily insulated and as airtight as possible. I'm an avid cook and will likely be relying on a range hood pretty regularly to help remove any unwanted odors or smoke from the house when cooking. I've read numerous threads about the challenges that one faces with ventilation hoods and the negative pressure they can create in airtight homes. I'm also aware that an air intake in such a home to offset this pressure differential can pull in a lot of unwanted cold air in the winter making a home quite thermally inefficient. I'm considering an option that may not be an optimal solution, but could address the pressure differential problem as well as still allowing the house to properly ventilate without experiencing a noticeable drop in temperature. Specifically, I'm looking at using a recirculating hood in conjunction with (but completely separate from) an ERV. I understand that such a range hood simply traps grease and controls unwanted odors above the range top, however any smoke or condensation generated are simply blown right back into the same space. My question is whether using a good ERV system simultaneously that has the added ability of preheating the incoming air in the winter would effectively be able to maintain the pressure balance, remove any smoke or condensation and stop any cold air from being pulled into the house. I'm picturing having an exhaust vent for the ERV located in the kitchen ceiling as well as having the controls for the ERV located near the range so an immediate air exchange could be performed at the same time the hood is in use.
Would this be an efficient ventilation system? What are the potential problems or inefficiencies I might be facing with such a setup?
John |
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ICFHybrid
Veteran Member
Posts:3039
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| 30 Jan 2012 09:06 AM |
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Well, the first problem would be matching an ERV capacity to the capacity of the recirculating hood. It would take about three ERVs entire capacity to match the volume moved by the hood.
What happens if there is a cooktop fire? How do the recirculating hoods deal with that? |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 10:34 AM |
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Posted By ICFHybrid on 30 Jan 2012 09:06 AM
Well, the first problem would be matching an ERV capacity to the capacity of the recirculating hood. It would take about three ERVs entire capacity to match the volume moved by the hood.
What happens if there is a cooktop fire? How do the recirculating hoods deal with that?
ICFHybrid:
I discovered looking at the specs of the ERV that there are two models made by UltimateAir: the smaller one has a max of 200 cfm (relative to 600 cfm for the hood) and the larger one can move air anywhere between 200 and 1,800 cfm, but is likely overkill in every other respect with a house as small as I'm building, not to mention cost. The larger unit is also huge, weighing 600 lbs and requiring 4 - 18" ducts! It's a good point you raise, and I'd likely have to rely on the smaller ERV to complete one full house exchange after using the range, which would take approximately 48 minutes for a house my size (the larger unit would do the job in 5 1/2 minutes.) I don't mind going the route of the smaller ERV as long as it does its job quietly and inexpensively.
Regarding a cooktop fire, I have to admit I never considered how I'd deal with that smoke. I guess in an extreme case like that, I'd rely on the ERV on its highest setting to clear the smoke out of the place. It's a problem I've never had to deal with and never hope to, but it's good to think through these things now.
Thanks for the input,
John |
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Bigrig
New Member
Posts:92
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| 30 Jan 2012 11:19 AM |
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The following is just my opinion, I am not a HVAC designer. I have seen recommendations to place a hrv/erv return grille in the kitchen (but well away from the range). Air flow will then be into the kitchen, isolating and eventually removing the contaminated ir. This allows the removal of odor without contaminating the hrv/erv with grease. In this case fire is not an issue as the exhaust should be well outside the fire area and any smoke it picks up will be vented outsde. In reality cold or not you will open a window to clear the smoke after getting any fire out (or the fire department will). As the hood is not connected to the erv the difference in cfm is not an issue. Still 600cfm seems rather a lot and I see NO listing for sound levels. I would certainly want to see one running at full speed in person before buying one. And remember that it will sound a lot quieter in an open showroom than your enclosed kitchen! |
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ICFHybrid
Veteran Member
Posts:3039
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| 30 Jan 2012 11:54 AM |
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but is likely overkill in every other respect with a house as small as I'm building, not to mention cost. Exactly. It is a commercial model and everything about it, including energy usage year after year will be overkill. It's like Bigrig says. Put an ERV exhaust in the kitchen to deal with normal excess humidity and smells, and put in a code-compliant exhaust hood to deal with the times that are too much for the ERV. Use a window for makeup air if code will allow that. Make sure the ERV exhaust inlet is far enough away from the cooktop such that it won't suck up oily residue, because that will be a maintenance problem. |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 12:02 PM |
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Posted By Bigrig on 30 Jan 2012 11:19 AM
600cfm seems rather a lot and I see NO listing for sound levels. I would certainly want to see one running at full speed in person before buying one. And remember that it will sound a lot quieter in an open showroom than your enclosed kitchen!
Thanks for the feedback. It's much appreciated. As for the sound levels, the particular unit I'd be going with (with recirculating hood) has a sound rating of 1.8 to 6.5 sones, depending on the setting used. Assuming I'd be running the unit at full capacity, this would equal approximately 55 decibels, using the formula dBA = 33.2 * LOG10(sones) + 28. Any idea how this compares to the typical range hood? John |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 12:16 PM |
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Posted By ICFHybrid on 30 Jan 2012 11:54 AM
but is likely overkill in every other respect with a house as small as I'm building, not to mention cost. Exactly. It is a commercial model and everything about it, including energy usage year after year will be overkill.
It's like Bigrig says. Put an ERV exhaust in the kitchen to deal with normal excess humidity and smells, and put in a code-compliant exhaust hood to deal with the times that are too much for the ERV. Use a window for makeup air if code will allow that. Make sure the ERV exhaust inlet is far enough away from the cooktop such that it won't suck up oily residue, because that will be a maintenance problem.
ICFHybrid: I'm going to be installing a 36" commercial range top that I've been told by the manufacturer will require the 600 cfm. I've actually seen many 36" range hoods on the market that are in the >1200 cfm range. I don't want to drop below the 600 cfm unless the manufacturer of the range top thinks it's a good idea. For the record, the range top will look something like this once it's installed. The particular recirculating range hood I'll likely go with looks like this and will mount beneath 12" tall cabinets. John |
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acwizard
Basic Member
Posts:265
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| 30 Jan 2012 01:33 PM |
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6.5 sones is fairly noisy.I would take a different approach to your design. There is a big difference in residential and commercial kitchen design.Your recirc hood is just removing large grease particles and dumping the air right back into the space. In a commercial design , make up air is brought in conditioned and exhausted thru the hood.Building pressures are controlled by the hvac equipment.There are very expensive systems that extract all grease and latent and sensible loads without dumping the air. Last one I quoted was over 100K dollars. Another point is that in a commercial application building codes are more strict and a greater concern for fire and property damage exists.Anytime the fan is located in the hood , you are going to have a noisy kitchen. |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 02:00 PM |
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ACWizard: Thanks for the clarification. I guess I didn't mean that I was building a professional kitchen, but rather installing a professional-grade range top that will be producing a much higher than standard amount of Btus/burner. A standard vent hood that has an in-line or external exhaust range hood just doesn't seem practical in a structure as airtight as I'll be building without introducing a whole other set of problems and inefficiencies, which is why I'm looking at going in the direction of a passive house solution for venting the cooking surface. I also wanted to point out that the two range hoods I'm considering ( 1 & 2) both have the option of a recirculating kit with carbon filters which will not only screen out the grease particles but most of the odors as well. I made a point of passing on all hoods that were simply an aluminum screen to catch the grease. Any idea what a typical sone/decibel rating would be for a 36" range hood with internal baffles? John |
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Alton
Veteran Member
Posts:2164
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| 30 Jan 2012 02:11 PM |
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Be sure to check with your local code official regarding fires and a way to automatically shut off the fans. In some areas I have been told that a heat-fusible link must be in the fan circuit to shut the fan off in case of fire. No reason to pump oxygen to a fire that is doing nicely by itself. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 03:32 PM |
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Alton:
I would never have considered this. Thanks for bringing it to my attention.
John
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JohnyH
Basic Member
Posts:114
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| 30 Jan 2012 03:42 PM |
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If it's electric you could do this but a gas or propane cook top would HAVE to be vented outside by code, at least in my area?
john |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 03:45 PM |
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I'm finding that building code in small town Maine isn't nearly as rigid as it is in most parts of the country. I will check it out though. Thanks.
John
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FBBP
Veteran Member
Posts:1215
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| 30 Jan 2012 07:37 PM |
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Posted By Litawyn on 30 Jan 2012 03:45 PM
I'm finding that building code in small town Maine isn't nearly as rigid as it is in most parts of the country. I will check it out though. Thanks.
John
Never the less if the range manufacturer says you need to exhaust 600 cfm than thats what needs to be done. If your ERV doesn't keep up than you will be gassing yourself. You can send 600 cfm's around in a circle but you won't take the flue gases out of it. Maybe some of the odour and grease. Maybe. What are you going to use for heating the house? It might be more economical sense to make sure your heating system can handle the extra btu's required for make up air rather than the resistances heat coils that would be required in a ERV. I honestly don't see any way that an ERV can keep up with that demand. |
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Litawyn
New Member
Posts:46
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| 30 Jan 2012 09:17 PM |
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FBBP: I'm going to call the code enforcement officer for my town tomorrow and find out just what he'd require. Ultimately, if it turns out that I would need to exhaust my range top at 600 cfm or more to meet code, I'd have to give serious thought to going with a system that does exhaust to the outdoors. I discovered a great thread on the GBA website that addresses many of the issues with properly ventilating a range hood in an airtight home. If I were to go the direction of a vented hood, I would want to have an air intake that could bring fresh air into the house when I'm using the range top by venting through a toekick beneath one of the kitchen counters, much like in this photo. I'd only want to do it though if there were a safe and cost-effective way of pre-heating this incoming air (much like the WarmFlo Duct Heater on the ERV intake.) Possibly one of these Make-Up Air Heaters on an incoming kitchen air duct would do the job. It could easily be installed between a pair of kitchen floor joists. The bigger question though is the cost/benefit. Would the expense of such a system (and of the electricity to run it) outweigh the nuisance and inefficiency of filling a warm kitchen with cold air every time I used the range top in the winter? It just seems crazy to me to build a thermally efficient home and basically be leaving a window wide open every time I cook--especially in the dead of winter. Thoughts? John |
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FBBP
Veteran Member
Posts:1215
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| 30 Jan 2012 10:09 PM |
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Posted By Litawyn on 30 Jan 2012 09:17 PM
FBBP:
I'm going to call the code enforcement officer for my town tomorrow and find out just what he'd require. Ultimately, if it turns out that I would need to exhaust my range top at 600 cfm or more to meet code, I'd have to give serious thought to going with a system that does exhaust to the outdoors. I discovered a great thread on the GBA website that addresses many of the issues with properly ventilating a range hood in an airtight home.
If I were to go the direction of a vented hood, I would want to have an air intake that could bring fresh air into the house when I'm using the range top by venting through a toekick beneath one of the kitchen counters, much like in this photo. I'd only want to do it though if there were a safe and cost-effective way of pre-heating this incoming air (much like the WarmFlo Duct Heater on the ERV intake.) Possibly one of these Make-Up Air Heaters on an incoming kitchen air duct would do the job. It could easily be installed between a pair of kitchen floor joists. The bigger question though is the cost/benefit. Would the expense of such a system (and of the electricity to run it) outweigh the nuisance and inefficiency of filling a warm kitchen with cold air every time I used the range top in the winter? It just seems crazy to me to build a thermally efficient home and basically be leaving a window wide open every time I cook--especially in the dead of winter.
Thoughts?
John
John - if you read the whole thread on GBA you know there is some different points of view. The most obvious answer given is "don't cook" Wow! All of a sudden I'm not so sure PH standards are that important! If cooking is a great thing in your life, then you are going to cook. This is why I assume you are using a gas stove. The GBA thread does point out the problems with downdraft venting. You need so much more suction to pull hot air down and than a lot will still escape. You may be able to decrease the require cfm's somewhat by using a bigger range hood. The bigger the funnel the more steam etc rises into it, the less cfm required to vent it out. Even if the hood has to be higher so as not to block the view, if it is six inches wider than the cooking surface, it will capture all the rising steam with little suction. Use a custom hood and put the fan outside to lower noise values. Make sure the fan can be run off a rheostat so that you can slow it right down unless you really need the full power.
If you are using forced air to heat the house, you can upsize it and interlock the fan with the furnace so that the furnace comes on when the fan is on. If you are using a boiler it is reasonably easy to add a fan coil unit to heat the incoming air. If you need to use electric resistance you will have to add that to the price of the steak you are going to grill ;-)
Bob |
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ICFHybrid
Veteran Member
Posts:3039
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| 30 Jan 2012 11:50 PM |
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I chose Vent-A-Hood to vent a 48" gas range. Vent-A-Hood has a feature they call the Magic Lung which enables you to use a lower flow rate than might otherwise be required. For example, my 54" hood exhausts 900 cfm while you can use it for installations otherwise requiring 1350 cfm.
I also selected it because it was noticeably more quiet at about 6 sones than any of the other brands I noise-tested. |
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Litawyn
New Member
Posts:46
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| 31 Jan 2012 12:20 AM |
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Posted By FBBP on 30 Jan 2012 10:09 PM
John - if you read the whole thread on GBA you know there is some different points of view. The most obvious answer given is "don't cook" Wow! All of a sudden I'm not so sure PH standards are that important! If cooking is a great thing in your life, then you are going to cook. This is why I assume you are using a gas stove. The GBA thread does point out the problems with downdraft venting. You need so much more suction to pull hot air down and than a lot will still escape. You may be able to decrease the require cfm's somewhat by using a bigger range hood. The bigger the funnel the more steam etc rises into it, the less cfm required to vent it out. Even if the hood has to be higher so as not to block the view, if it is six inches wider than the cooking surface, it will capture all the rising steam with little suction. Use a custom hood and put the fan outside to lower noise values. Make sure the fan can be run off a rheostat so that you can slow it right down unless you really need the full power.
If you are using forced air to heat the house, you can upsize it and interlock the fan with the furnace so that the furnace comes on when the fan is on. If you are using a boiler it is reasonably easy to add a fan coil unit to heat the incoming air. If you need to use electric resistance you will have to add that to the price of the steak you are going to grill ;-)
Bob
Bob:
Thanks for the informative post.
I never considered going with a slightly larger hood than
the actual size of the range top, but now that you've explained the benefit of it, it
makes perfect sense. One of the two 600
cfm hoods I was originally considering as a recirculating hood is also available
as a ducted model in both 36" and 42" widths. I'll likely go with the 42" model given your
explanation. The rheostat is a great idea, too. It does have an internal blower though (6 sones.) Practically all of the external ducting units this size are 1200 cfm which I only see as causing problems in an airtight house. Even if I went this route, I'd likely only ever use it on low or medium. I'll probably stick with the internal blower model.
As for heating the house, I'll be using an efficient wood pellet stove as the primary source of heat, with a heat/cool pump ductless split on the second floor of the house as a back-up heat source as well as for A/C. The whole house is estimated to require no more than 12,000 Btu/h to keep it at 72F indoors when it's -15F outside.
Would there be a way to use the heat that's being ventilated from the range hood to help pre-heat the incoming make-up air? It just seems like such a waste to be blasting all of that energy outdoors without somehow harnessing it as a pre-heat.
John
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Litawyn
New Member
Posts:46
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| 31 Jan 2012 12:43 AM |
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Posted By ICFHybrid on 30 Jan 2012 11:50 PM
I chose Vent-A-Hood to vent a 48" gas range. Vent-A-Hood has a feature they call the Magic Lung which enables you to use a lower flow rate than might otherwise be required. For example, my 54" hood exhausts 900 cfm while you can use it for installations otherwise requiring 1350 cfm.
I also selected it because it was noticeably more quiet at about 6 sones than any of the other brands I noise-tested.
I like the 36" model with the Magic Lung. I'm going to look at this unit a bit more closely. It does seem odd though that Vent-A-Hood would claim their hoods are "the quietest in the industry," yet nowhere in their literature actually quantify just how quiet. If your 54" model is 6 sones and 900 cfm (equivalent to 1350 cfm,) I'm curious how much quieter the 36" / 600 cfm model would be. Any ideas? UPDATE: I just visited their website and discovered the following: the 900 cfm blower is rated 6.3 sones (at high speed) and the 1200 cfm blower at 6.6 sones. Oddly, the 600 cfm blower is slightly louder than the 900 cfm unit and measures 6.5 sones. John |
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ICFHybrid
Veteran Member
Posts:3039
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| 31 Jan 2012 01:16 AM |
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yet nowhere in their literature actually quantify just how quiet. Vent-A-Hood actually publishes more noise info than most of the other major brands. If you look at the right documents there, you can find the noise info while I was never able to find comparable numbers for the others..... The conclusion I drew from that is obvious..... However, during my shopping, I also visited a number of demonstration kitchens set up at appliance sales places and found that the other brands appeared to be louder than the Vent-A-Hood. |
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