Replies

1. 
   DIYdoc | Feb 12, 2005 11:30pm | #1

   Take what I say with a grain of salt, since I'm not a HVAC engineer, but I'd guess that you don't even need to force the intake air with a fan.   Just a power damper that opens with the exhaust.   The exhaust will simply pull on the intake. 

   The differential in the size of the duct work will probably be OK, since the velocity of the air will likely be higher in this duct than in your exhaust duct.  At the very least, you will have enough pressure equalization to avoid backdrafting the fireplace.   However, I'd be worried if you have a couple of elbows in the intake-more resistance to flow.

   Any engineers out there?

   Steve

2. 
   DanH | Feb 13, 2005 12:15am | #2

   You should have makeup air vents near the fireplace.

1. 
   draket | Feb 13, 2005 07:11pm | #3

   "You should have makeup air vents near the fireplace."

   DanH

   I do have make-up air vents near the fireplace. It is a Rumford fireplace with an air vent on each lower back side. I still think the kitchen exhaust (when cranked up) may cause back-drafting.

   Steve

   I was initially only going to install a passive vent (like you mentioned), but I heard that a passive make-up opening should be twice as large as the exhausted vent size.

   I don't have room for a 24" vent.

   !0" is about all I can get in there. That is the reason for the second fan.

   Still need to figure out a way so when running the large fan at 1/2 speed (which will be the majority of the time), the smaller fan is running at 3/4 to full capacity.

1. 
   DenverKevin | Feb 17, 2005 08:32am | #4

   Is it too late to install a real exhaust hood? When they are this big, I believe they are required to have one fan each for exhaust and makeup air. Another advantage is that the cold makeup air is delivered right above the stove, so it gets exhausted before you have to pay to heat it up. (or cool it down)

1. 
   draket | Feb 17, 2005 09:16am | #5

   Kevin

   I have not installed anything yet. Still some time to figure it out.

   I'm not sure what you mean by " a real exhaust hood"? 

   My hood will be custom fabricated and will sit up above the range. It will have the grease baffles and some lighting only. The exhaust fan is inline and remote, half way up the 12" duct on the way to the roof (this reduces kitchen noise). The air from my make-up fan would enter just below the kick of the range. This make-up fan will be below the floor and in the crawl space.

   When you say a second fan that provides the cold make up air right above the stove..

   I can't imagine providing a 10" to 12" duct right above the range. Unless the opening is right up there in the exhaust hood next to the exhaust duct. If this is the case, I can't see how that would be effective at pulling smoke and grease from the top of the stove up into the exhaust. I think it would just take the majority of available air directly from the make-up fan without pulling the heat/smoke/grease up with it. Going out one duct right into the other with no time or area coverage to do anything.

   I believe the make-up air has to start below and in front of the range in order to effectively carry the heat/smoke/grease up and away. Or at least right at the surface of the range (is this what you meant?). But how do you do that while making it look nice?

1. 
   DenverKevin | Feb 17, 2005 09:39am | #6

   Sorry,
   I misremembered some of the things in this article: http://homeenergy.org/archive/hem.dis.anl.gov/eehem/99/990113.html#design
   There are a lot of things to consider with a fan this big. The first should be can I go a lot smaller.

3. 
   TRice | Feb 17, 2005 04:46pm | #7

   First, I can tell you what I would design for a commercial kitchen.

   The makeup air system, usually a direct fired unit ducted directly to a compensating hood, would provide 75% of the exhaust volume. If the hood is a simple (i.e. exhaust only) then make up air would be provided in the immediate area around the hood via ceiling diffusers or registers. Commercial Type-II Kitchen exhaust hoods, the type that are suitable for installation over deep fat fryers, are either UL listed for the equipment under it or are setup to exhuast 100 cfm/sq.ft. Grease ducts are heavy (14 ga) black steel with welded seams and are sized at 1500 to 2000 fpm velocity.

   Now, for a house, even with semi-commercial cooking equipment, is completely different. BTW, your 12" exhaust duct and inline fan will NEVER pass 2000 cfm. Depending on the restrictions in place (filters, duct, wall/roof cap) I would expect half that. Same for your 10" makeup duct/fan, expect maybe 700-800 max. Ratings on these fans are typically at 0" of static pressure.

   To determine the best way to provide makeup air for your hood, some more information is required. What type of HVAC system is in your house? One option is to provide fresh air to a forced air system tah operates via a barametric damper. When the space pressure drops, the damper opens and allows outside air to mix with the system return air to makeup for exhausted and/or combusted air.

   It would be easy enough to tie the supply and exhaust fans together if you wanted to do that. If you wanted to temper the fresh air seaparately, then it would be a little more complicated, but possible.

1. 
   draket | Feb 17, 2005 08:22pm | #8

   Timbo

   Thank you for your reply.

   I am aware that the 2000cfm will not actually pull that many cfm's. That is why I went with a fairly large fan to start with for my residential application.

   My home is heated with in-floor radiant heat. The house is SUPER-insulated and VERY tight.

   Most of the time our weather is mild but I have a few concerns during the few colder months, or whenever the outside make-up air is significantly colder than the closed-up house (usually the same time the fireplace might be burning).  I would prefer my make-up air come from the immediate area of the range in a matter that most effectively carries the smoke, grease, and heat out of the range to the exhaust hood. I would imagine the air would perform best if available directly below the front of the range creating a smooth directional flow to the exhaust catching the smoke and grease on it's way.  I understand the concept of providing make-up air elsewhere in the home, but I definitely do not want to have to condition (heat) the make-up air. At the same time I do not want to pull cold make-up air from across the room, another part of the home, and most importantly from my near by fireplace, possibly causing some back-drafting.

   I'm sure my exhaust system would be very effective, I just want to maximize it's potential and figure out a way to wire the speed control with the two fans so that the smaller make-up fan runs at it's higher capacity in comparison to the capacity of the larger exhaust fan.

   Perfect scenario for most common cooking:

   Speed control turned on to half speed .

   Large fan running at 50% capacity (realistically about 500 - 600 cfm). while the smaller make-up fan in running at 100% capacity (realistically about 500 - 600 cfm). I know if I crank up the speed control from there, the larger fan will increase and smaller fan is already maxed out.  I can live with that. Venting at full speed will be seldom and I can always crack open the kitchen window for those rare instances.

   I would think there has got to be a device and a wiring option that can do this?

   Any comments?

   Thanks

1. 
   TJK1141 | Feb 17, 2005 08:53pm | #9

   There are heat recovery ventillators that can address the make up air temperature issue. I'm not sure one unit can handle 2000 CFM though.

2. 
   TRice | Feb 18, 2005 06:59pm | #10

   I dont know what kind of access or space you have immediatly beneath the cooking area. Given that you have a variable speed exhaust fan and a boiler, with access and space, an ideal solution would be as follows:

   Let say on max speed, the exhaust moves 1200 cfm and plan on makeup of 900. Outside air gets to 0 and you want to temper the air on that day up to 65. This would require about 63,000 btu, a hot water coil, 3-row, 16x12 and about 8 gpm off of your boiler, 1" or 1-1/4"  piping, a control valve set to maintain the "discharge temperature at 65, a 2-speed inline fan, 16x8 duct and probably about 4 floor registers at 225 cfm max apiece. Intrlock the supply low speed with the exhaust fan and run the high speed from a pressure switch tapped at the inlet of the exhaust fan. Or control both with a HD speed controller.

   Rough estimated costs, hw coil - $200, 1/25 hp circ pump $75, fan(a cheap commercial grade 2-sp is ouch $900+) inline 120V $700, plus you can count on a couple hundred for piping, ducting, wiring, etc.

1. 
   draket | Feb 18, 2005 09:46pm | #12

   Timbo

   I was not planning on tempering any make-up air, but you make it seem worth while.

   How would you adjust your recommendation to to fit my actual climate temperatures (Northern California)?

   Even in the Winter the temperature rarely gets that cold. The average winter low is 40 degrees. The average winter high is about 60 degrees.

   With this information would you change anything from your last post?

   I have good access and space under the kitchen.

   Could you also recommend a good brand name hot water coil?

   Thanks much

1. 
   TRice | Feb 22, 2005 08:14pm | #14

   For the heat required to temper the air, you can adjust it as follows:

   dTxcfmx1.085 = btu/hr . For 1200 cfm, 30 degF outside and supply air @ 70 degF,

   heat required is 1200x1.085x40 = 52,080 btuh or 52MBH which would require 5 - 7 gpm of hot water, depending on the temperature drop in the water across the coil.

   This is still going to require a 2-row coil, 1" piping (3/4" would work). There are a lot of coils available commercially. Trane, USA Coil, Magic Aire, HeatCraft are a few of the major brands with which I am most familiar.

   I represent Magic Aire. A mechanical cintrcator can expect to pay $100 - 120 for a small (12x15 or so) 2-row coil.

   You could try with out heat and see how you like it. I don't know how much I would tolerate 40 degree coming in to my kitchen. That would be a personal choice and might be best made after some experience with the system setup and operating for a few seasons. Practiaclity would say that the few days a year it really gets cold, don't run this at full blast. Choose a mild day cook that blackened catfish. Different strokes apples, but for me personally, in the winter when I making soups, stews, chili , etc., I kinda like the aroma (and humidity) stay in the house.

2. 
   draket | Feb 22, 2005 08:58pm | #15

   Timbo,

   Funny, I was just on the phone this morning with Jodie C. (tech support) at magicaire.

   He was very helpful setting me up with the right model for my application.

   Thanks for your help and well-taken advice!

4. 
   SEBDESN | Feb 18, 2005 09:29pm | #11

   2000 cfm is big time overkill. I have a 1200 and have a rest. type gas broiler/grill that is in addition to the 5 burner cooktop. It works just fine. And I crack the window,but only if its running full on.

1. 
   draket | Feb 18, 2005 09:59pm | #13

   SEBDES

   I already own the 2000 cfm fan so it's what I will have to go with.

   Because of my height, the design of the kitchen, and for aesthetic reasons, the vent hood will be hung very high above the range-top. I think most vent manufacturers (mine will be custom made) suggest hanging the vent at a maximum of 28" to 30" above the range. Mine will be hung about 48" above.  This is another reason for the extra cfm's needed to pull up all the grease and smoke.

   If I don't need all that, I always have the speed control to use only what is necessary.

   Overkill? possibly.

   But better safe than sorry.

5. 
   CharlieYXu | Jan 11, 2022 11:48pm | #16

   Hi Drakes,

   Curious what did you do eventually to your makeup system . Air right house / fireplace / powerful kitchen hood sounds a very contradicted combination and it is exactly what I want too for my house. Plus I am in a cold climate zone ! How does your system work out ?

   Thanks
   Charlie