Can we solve a cold and windy problem?

[neptunebob]

Like many kitchens, in my house we have a range hood above the stove that exhausts to the outside right out the back.  It is cold today, and I just noticed, it is drafty with cold air coming in.  There are two aluminum flaps that close, one on the hood itself and one on the part that sticks outside but still lots of cold air.  I am sure this has been going on for decades but I was wondering if anyone here, maybe working on high end homes, know of any way to solve a cold problem.  Would it help if there was a bend in the ductwork (rather than go straight out the wall)?  Do the high end hoods like Gaggenau somehow close themselves off?

 

I know some people just have fan recirculate into the kitchen but then what is the point in having a range hood?

 

Right now, as in the past, I might just have to duct tape plastic to the hood but I don't think the owners of "trophy kitchens" do this.  

 

[combo52]

Air leaking back into houses through Range hoods, etc.

Hi Bob, this can be a tough problem. This can happen with dryer vents and exhaust fans and bathrooms, etc. as well, our house has 12 vent fans, clothes, dryer vents, etc. and I don't have trouble with any of them, but you have to really get a very high quality hood some of them have magnets or springs in them to hold the damper closed.

If there's not something holding the outside flap open, I would look for a better quality hood assembly and replace it. That's about all you can do taping plastic over it of course, makes it as useless as having a ventless hood because then you can't use it when you really need it.

Two of the clothes dryers that I installed most recently, I had to put a in-line back damper in the exhaust duct because I was getting too much cold air back through those.

But since you're exhaust hood goes directly through the wall, you're just gonna have to get a very high quality hood with damper and install it to solve this problem.
If you have forcedair heating in your house, your house should be slightly pressurized. You might have a problem with your heating duct design often times a duct should go outside from your return vent so that your forced air furnace is slightly pressurizing your house. This also can minimize this type of problem

John

 

[neptunebob]

Actually, we at one time did have a duct outside...

You know how sometimes a builder will create a return duct by enclosing a joist space with the plywood floor and drywall ceiling?  Our builder cheaped out and had an opening onto the front porch roof, sending cold air right into the furnace.  It was years later that I found it and sealed that off.  

 

I thought of having a wire on the outside cap damper that would go inside so to make it possible to hold that closed.  Pictures coming soon.  

 

I did not really want to have a bend because then the hood would not exhaust as well.  Would 2 90 degree elbows make much difference?

 

This house was built in 1972 before they had Tyvek house wrap.  The sheathing is some kind of tar fiber material called Gold Bond.  Even though we have sealed off a lot of leaks, I think plenty of air still gets in that we won't suffocate like I hear could happen in super tight houses. 

 

There is always a slight suction like you might find on a downtown building where it is hard to open the door, but less.  I think a lot of air goes up the flue to the "regular" water heater which is a rather large pipe.

 

Combo, when you mean very high quality hood do you mean like Wolf, Miele, Gagganeau?  

 

[DADoES]

 
<blockquote>Would 2 90 degree elbows make much difference?</blockquote> Each 90° elbow on a dryer exhaust, for comparison, is considered equivalent to 5 feet of length regards to effect on airflow.

 

[combo52]

High quality outside vent hoods

Hi Bob, I'm talking about just the little vent hood that's on the outside of the house not the thing that's over the range , range hood sometimes don't have a damper in them at all, and most of them are not very effective.

Having a longer pipe run with elbows would do almost nothing for reducing cold air infiltration you have to keep it out of the house at the outside, where the flap is.

 

[petek]

Mine is straight out the back. There's an awning flap on the outside vent that just opens (gets blown open) when the exhaust fan runs and shuts itself via gravity when the fan is off.. simple mechanism. Perhaps yours is stuck or you don't have one?

 

[tomturbomatic]

When my range hood was installed in the 90s, a magnet was attached to a tab on the damper that held the damper closed against the outside hood surround. It was very effective at preventing back drafts.

 

[gizmo]

I have a rangehood with stainless steel wall outlet directly behind the rangehood. It works fantastic. The wall outlet has a stainless steel hood over it, with a flap valve behind that falls shut when there is no air flow. It allows no back flow, though when the wind blows the right way, it creates a suction that lifts the damper flap a tiny bit, you can hear it bouncing back when the wind subsides, there is a rubber seal the flap closes against and it makes a faint tap sound when it shuts. But I never get air blowing back into the room.

 

It has a mesh screen inside to stop flies getting in and for fire rating requirements, about once a year I have to remove the vent from the wall and clean the mesh.  Unfortunately the mesh is accessed from the duct side, would be smarter if it accessed from outside.

 

I used to have a different rangehood that vented up, through a cupboard above the rangehood, then turned 90 degrees through the wall into the eave space, then down 90 degrees out through the eave lining. (I think that is called the soffit in USA??) Since changing to the rear-vented rangehood out through the wall, I have gained back cupboard space, lost an ugly duct above the cupboard, reduced rangehood noise dramatically, and the rangehood works 100% better. Short ductwork is better. If you have back flow problems, you need a damper flap like the one in the link below.

https://www.mitre10.com.au/kensington-hooded-wall-vent-marine-grade-stainless-steel-with-mesh-insert-150mm-3242187

 

[neptunebob]

Here's a cold update!

I installed the hood called Broan.  I found that a lot of the draft was actually cold air going Around the duct, so I used the foam can to seal that up.  Some of the bricks fell off (the mortar was never any good) and the draft hood along with the damper in the hood itself keeps most of the cold out, there is just some draft.  

 

Good to have a vented hood again, keeps a lot of odor out. 

 

With all the air we exhaust out of our houses, is there such a thing as a heater duct that would let outside air in and preheat it so it is not brutally cold?

 

I know they have those energy recovery units but they are expensive and it seems that we need air coming in and don't need it going out.  

 

I worked at a large nursing home that had a ventilation system like this, if not for this system the place would smell of high heaven.  It was a large duct from outside that went through what looked like a semi truck radiator to heat the air in winter and had cool water in summer so it is not brutal cold or stinking hot.  

 

I know that restaurants have make up air systems for their hood fans but those go all day and when turned off at night, who cares about how drafty it gets.  

 

I have some pictures to try to show what I did.  This spring I will have to climb up a ladder and make a neater job outside. 

 

[neptunebob]

Here's a cold update!

 

[henene4]

In Germany, when you install a wood fired fireplace or similar in a living space, you have 3 options:
1. You don't have an exhausting vent hood.
2. You have a window switch that doesn't allow the hood to operate when that window is closed.
3. Your fire place has an external air supply.

All to prevent any air flowing back.

Same goes with new high efficiency housing. You - usually - don't get exhausting vent hoods to allow all air exchange to happen through the active ventilation heat exchange units.
It's actually assumed such a vent hood could increase your usage by up to 20kWh/m² a year in such cases.

The assumed operation principle is actually that a vent hood pulls as much air from as many places as possible.
If it would pull air directionally from one side, a surprising amount of odour could draft out in other directions.

What there is is hose vent flaps, just motorised.
Those are usually used in higher grade scenarios - like venting lots of appliances to one central exhaust - and open via a motor every time you turn on the hood.