One thing I dont see a lot of discussion about is making up air for a kitchen exhaust. I have a spray foamed house and I plan on running the bathroom fans through an ERV.
But we cook a lot (and greasy stuff like stir fry, bacon & eggs, etc.) so I can’t get away with running the kitchen through the ERV. The hood I’m using is a whopping 715 CFM (at high). Where is that make up air going to come from? All gas appliances are sealed combustion so I can’t backdraft anything. I have tight windows and doors, all plates are caulked, etc.
Should I just not worry about it and let it be (just won’t get full volume from the hood)? It doesn’t feel right….I’d like to have a pressure detector in the kitchen and some kind of system that opens a damper and pulls in fresh air (possibly through a heater for the winter)? Does such a thing exist?
Maybe I could wire into the hood and kick in some make up air into the basement with a grill cut in the floor to allow air to flow from the basement into the kitchen area. At least I would get some conditioning of the air via mixing with the basement air (most of the basement is my workshop so cold air coming in there won’t bother me all that much).
-MERC
Replies
Doesn't sound like your house will be very leaky. Any reason you aren't planning a whole house air system?
If that's what your ERV is, size the incoming fan larger to slightly pressurize the house, causing leaks to go out. Much more comfortable that way and would give you some cushion for your intermittent kitchen exhaust.
That's what we do, very satisfactorily.
PAHS Designer/Builder- Bury it!
Thanks for the reply. If I remember correctly, you run your kitchen hood through your HRV right?
I like the thought of pressurizing the house and I think I'll do that. Honestly I'll probably need more than one ERV, we'll see how the budget goes. It still seems like I need something that will match that vent hood, one for one when it is running. I guess I could just pull out my old EE background and build something.
I guess I was thinking an ERV or two would be my whole house air system. I already have a forced air furnace, but I need something to do the air changing. I just haven't gotten deep enough into that to know what it is yet.
MERC.
Edited 12/7/2004 1:50 pm ET by DJ Merc
Your ERV or a HRV should have been adjusted when it was installed by an "air flow measure (magnahelic insrument) this measurement ,if done properly by a hvac pro will take into consideration other applances that may be running so as to avoid any 'negative'/ positive pressures within the home, thus the so-called 'make-up air is drawn from the fresh air intake that the erv/hrv is giving it..
Said ERV is not yet installed. Are you saying the ERV will be adjusted to provide enough positive pressure such that when running my vent hood it will net out to a positive or zero pressure difference? Seems like that ERV would be running at a much higher speed than necessary just to overcome the occasional kitchen hood usage. I think an active system that kicks in when the hood kicks in is a better solution.
How come HVAC industry just doesn't seem to have it figured out?
MERC.
Ah, but the HVAC industry HAS it figured out.
Its because YOU aren't up to date on this Technology
Controlled ventilation systems operate most of the day, and some never turn off. Passive air vents are installed to make-up any air that is nearing a depletion (negative)state,as it would be in the case of this absurd 715 cfm hood.
what is this ,the kitchen at the waldorf?
Btw, what type of heating do you have? If its a ducted forced air system, then your in luck if you want to install a few gadgets that maintain a neutral pressure (pressure balanced)thru-out the home, and very economically too.
Edited 12/7/2004 3:40 pm ET by Hube
Edited 12/7/2004 3:42 pm ET by Hube
710 cfm fan = kitchen at the waldorf ?
The fan at my sister's home is a Thermador which pulls 1400 cfm. It is a residential unit that mounts on the side of the house. Even that wouldn't do squat at the waldorf.
carpenter in transition
I stand by my assertion that the HVAC industry doesn't haven't it figured out. Maybe the real answer is that it is figured out, it just costs a lot of money to make it right and therefore few have seen such an implementation. Where as, for example, you can pretty much install a basic bullet proof electrical system for reasonable cost and commonly available materials, HVAC seems like a whole other world. I also note that the HVAC trade (people and suppliers) hold their cards close and generally treat me like an idiot when it's obvious that I'm not that clueless, just need some help with a few details. That is always a red flag that something is amiss with the industry. But I'd be willing to accept the argument that you can build a wonderful system, it will just cost some money.
I admit the hood is a little overkill, though maybe not for the wild stir fry nights that I have. The grease really flys out of the wok. At any rate, it was the only decent looking hood I could find in 42" width chimney style, so that is what we are using.
I have forced air which I plan to run 4 zoned for the entire house, provided I can find a reasonable chase to the 2nd story from the basement. I thought about putting some kind of controller on the furnace blower that would help maintain correct positive pressure in the house zones. Just need to find said piece of equipment and controller for it. I'm sure if I strolled into my local HVAC supplier, he wouldn't have any clue what I was talking about.
MERC
You might try asking over here.http://hvac-talk.com/vbb/BTW, you want to ask it in terms of asking that you are learning what it takes to make a good system to help qualify an HVAC contractor.I have not lurked overthere in a while. But in the past they appear to be very helpful, but if it appears that you are doing to DIY HVAC then they will start attacking.There are barametic dampners that will open on pressure differences. But I don't know how they work with a HRV system. Do don't want the dampner to open all the time because of a pressure imbalance from the HRV.But one trick that I saw in FHB is to put the dampner behind the refigerator on the outside wall. That way the heat loss off the refigerator helps temper the air.You can also have an intake fan setup to run when the vent fan is running, but I have no idea how to size it.
Hvac, as you probably know ,deals with many, many hours of study and training. Especially , 'AIR BALANCING', its a almost a trade itself.
Most persons do not have clue about air measure, flow, quantities, cfm, fpm, static pressures, Vol, Vel,duct design ,etc, etc.
And that is why some dealers put a lid on some information to a diyer.
As soon as the diyer opens his mouth, a trained person can tell just what level this person is at.
A lot of hvac adjstments can be very deadly and disasterous if not done precisely.
Speaking of HVAC. I am sure if you get complicated . . . well then it can get complicated. However, I built a 2200 sqft house with my father 30 years ago. Installed the furance and ran the ducts. Never had a problem. Gee size the furnance, run enough heat ducts and don't go short on cold air returns, and . . . .
Do you really need more?
It seems pretty stupid to build an air tight house, and then punch a hole in the wall in order to pull in fresh air with thousands of dollars worth of gear. And oh yeah, such fireplace smoke from the livingroom into the kitchen. Brilliant! And people pay how much for such marvalous systems?
The problem with your leaky house is that you can't control where the air coming into the house will come from. It will probably be coming in through the walls.
Scenario 1: Summer time and it is hot and humid out, your AC is on, you turn on your 750 cfm fan, your make up air comes through the leaky walls and will condense somewhere in the wall. Even without your fan on moisture will travel throgh your leaky walls because we all know moisture moves from warm to cold.
Scenario 2: Winter time moisture will move through your leaky walls from inside to outside and condense somewhere in the wall.
Scenario 3: Turn on your kitchen fan and your make-up air comes from the garage or your vetilated, unconditioned, damp crawl space.
If HVAC was so simple, why aren't there more people in that line? It's not just "put in a furnace, hook it up and have enough ducts". If the ducts are too small, they either won't move enough air or the air that goes through will make too much noise and turbulance. If they're too small, the conditioned air won't get to the destination at the correct temperature. Too many bends and restrictions, laminar flow goes away and you get noise and not enough movement. Most air infiltration comes in around doors and through windows that don't fit well or aren't sealed properly and from leaky walls and holes where pipes, wiring and ducts are not sealed properly and the cold air goes from attics and outside to the heated space. Negative pressure compounds this problem by literally sucking the cold air in. It also draws outside air in through chimneys where exhaust gasses are moving and this brings CO along for the ride. Contrary to some people's opinion, bringing air into a well sealed house to the furnace with an inducer blower does not affect the air in the house. That's combustion air, specifically so the furnace doesn't blow heated air out and suck cold air in. As long as a very slightly positive pressure is maintained, cold air isn't sucked in and people don't die from CO poisoning.
"I cut this piece four times and it's still too short."
You're right HVAC is not easy, well the H and AC aren't to hard its the V thats the problem. If you are not using sealed combustion appliances you are asking for problems. Your right in that having a negative pressure in your house will suck air into the house, Positive pressure will do the opposite which is bad especially in the winter moisture can condense in the wall.
It's only going to condends in the wall if it can get into it. On a newer home, the vapor barrier should work if nobody added home theater wiring and stuff like that and punched holes in the outside walls. The doors are a more likely candidate for leaking, the windows next if the other plumbing and electrical holes were sealed. Every house will breathe a bit. Some just breathe like a heavy smoker running a marathon. If it's too well sealed, opening and closing doors is just weird.
"I cut this piece four times and it's still too short."
I got rid of my crawlspace and I use sealed combustion appliances. So I don't have anywhere to draw "bad" air from. I also sprayed my roof deck to do as much as I could to shut down the stack effect. Since my walls are spray foamed there is essentially zero air movement through my walls. So it's going to come from somewhere and I'd rather it not be "by chance" because who knows what hole it will find.
I think the motorized damper in the cold return will do nicely. Just need to dig around and find an appropriate part to do that and then figure out how to break into the wiring on the vent hood and open/close the damper with the hood.
Another choice would be to see if I could come up with some way of mounting the stove top so it had a small gap all the way around and then I could draw make up air from under the stove, draw up and around it, grab the smoke and grease and out the hood. An 1/8" gap all the way around a 36x30 rectangle is 16.5 sq in, which is about half the cross sectional area of the outgoing duct. So the air velocity would be about tornado level coming through that gap. Better come up with something else.
MERC.
Any heating supply house should carry motorized dampers and there are current sensing recepticles that can turn a second device on when the first causes a spike in voltage, like what is used for dust collectors when another powertool is turned on.
"I cut this piece four times and it's still too short."
" you say; your local hvac supplier would'nt have clue"...
then go to one that does I,m sure there are some in your area,.
What about a blower that is specifically for bringing air from outside to the underside of the hood and turns on with the hood? That way, you aren't making the whole house cold, and it can't be left on for too long. Do you have a high BTU range, too?
"I cut this piece four times and it's still too short."
I like the idea since the stove top will always be quite hot when the hood is on high, therefore cold incoming air in the area of the hood would not be noticed. I'll have to give this one some thought. The stove is a 36" 5-burner with a couple of 15k burners, one 10k and two 8k (I think).
I also like the behind the refrigerator as suggested, though that might be physically challenging and the architectural committee (wife) might not approve the outdoor grate on the backside of the refrigerator.
MERC
Since the hood is vented outside, why not bring it in behind the range? If the vent opening has enough area, the incoming air won't be moving too fast and should be fairly quiet. If there's unfinished basement space under the range, that would seem to be ideal. To me, anyway.
"I cut this piece four times and it's still too short."
Would this vent be a flapper type or something that closed by gravity when the hood is off?
MERC
If you put the make up air close to the stove it will short circuit and not work properly. Put a motorized damper into the cold air return ducted to the outside. Have it wired so it will open when you turn on your kitchen fan. The air coming in will be filtered by your forced air system and all the make up air won't be coming from one area. Stirling makes an erv that will measure the outside pressure and makes the inside pressure the same, It takes this measurement every ten min. so it wouldn't work for make-up air. I would avoid keeping your house under a positive or negative pressure you want it to be the same inside as outside.
Well, in my limited experience, if you get an installer through the gas company, he's likely to be wedded to a fairly simple technology, probably somewhat behind the times. If you find an installer through one of the high-end suppliers who deal with big stoves and appliances, you may be a lot happier.Your recovery unit should be sized/tuned to allow for the maximum amount of exhausted air, that should include any open fireplaces (some people still do this !) and hoods..
Phill Giles
The Unionville Woodwright
Unionville, Ontario
I shut down a resturant that was drawing negative pressure through sewer traps. It would also have comne through a vented gas device.
I have done quite a bit of inspection work with state inspectors and have learned a little . Ive worked out a few problems like you have now.
The only way to "effectively do it ", is to bring in make up air when the hood is running . No biggy. Run a wall vent or from a roof vent a 4 to 6 inch pipe or flex line with incomming air via an inline fan switched to come on when the hood is on. when the hood is off , so is the incomming air. It would be best to make the incomming opening close to the draw so that temperature in the room is not afffected.
Commercial type 2 or 3 hoods allow the same make up air in them . But you can make it your self.
Tim Mooney
If I remember correctly, you run your kitchen hood through your HRV right?
Your memory serves you well. And for your cooking, I'd reroute the ductwork. But unless you have a tiny house, you can plan for removing that amount of air for 20 minutes without making a major incoming leak.
2 ERV's? How large is your house? Take a look at your volume and see if your exhaust fan will be significant. If you have 40k cu ft, I can't imagine you would notice your fan's intake.
We have 20K cu ft that we're changing, .5ACH. I don't think your exhaust would make much difference if I upped the intake fan a few cfm. Our exhaust fan is a recycled one, no idea of cfm. It works very well with our over-sized hood. I did, for the inspector, have it bypassing our heat exchanger. Wasn't a problem. The change was primarily for my peace of mind. Sounds like you have a similar desire.
Clearly you can have a fine tuned system with multiple parts and get something more efficient than ours. Payback on the system will be never and I'd be very surprised if a visitor could tell the difference. PAHS Designer/Builder- Bury it!
My house volume is about 41k cu ft, spread over three floors, including basement workshop and storage room. Top two floors are living space and are about 27k between them. So if I run a 715 CFM fan for 20 minutes that would produce 14k cu ft of exhaust or about 0.3 air changes / 20 minutes = 0.9 ACH. That seems pretty significant to me. I sure would feel better if I knew where that volume was coming from. I guess like I said before if I don't provide a make up air path it will just choke the cfm down to what it can do.
I was planning on two ERVs because of the issue of chasing even more ductwork between the floors. I still haven't fully come to grips with what a good ERV installation looks and feels like so the design is still in flux. I'm not planning on closing up anytime soon so I have some time to give it some thought and play around with it. Since I'm chasing an HVAC feed and return to the second floor, maybe I can tie into that somehow though I read the JLC article and they said tying into a furnace ductwork doesn't make the best ERV installation. Might be good enough for me though.
I think I'll go mill about at hvac-talk.com.
MERC.
So if I run a 715 CFM fan for 20 minutes that would produce 14k cu ft of exhaust or about 0.3 air changes / 20 minutes = 0.9 ACH. That seems pretty significant to me.
And it will be, if you don't plan for that make up air with a pressurized system. See how simple it is? Size your fans. With that size volume you have significant latitude.PAHS Designer/Builder- Bury it!
Yes I think I see where you are going now. I'm glad I asked the question and I will contemplate for a while and see what I can come up with.
Thanks -MERC
Crack the window when you have it cranked up to 10...I have a 1200 cfm (unit on the roof), and a gas restaurant type grill on the peninsula. When its up to 10, I crack the window.Its only at 10 when the grill is on,and smoking however,otherwise its not a problem. The d-mn thing will suck the smoke from the fireplace in the front room all the way to the kitchen.Dont ask how I know that..
I didn't read all 30 posts, so maybe this has been covered, but does building code come into play?
Around here a fan that big requires not only make up air, but warm air.
I have seen inline fans installed, switched to the fan speed control, and vented behind a fridge.
Just a thought. Darren.
I just figured out how to do this.
A current sensing relay (Aprilaire A50, an HVAC part, $30) installed on the wire powering the exhaust fan will close a 24 volt circuit. You will need a 24 volt transformer and a Honeywell power operated damper.
I installed this on my return air duct which exhausts directly behind the range. It goes on when the fan goes on and provides enough makeup air directly from the attic to prevent backdrafting down the chimney or other such annoyances.