Makeup air requirement for range hoods over 400cfm

[jaylectricity]

I just learned about this code from the 2009 IRC. For anybody who doesn't know, if you have an exhaust hood at a certain cfm (400, usually) that exhausts to the outside you must have a way to makeup the air pressure. Apparently they're worried about the hood drawing air through the chimneys and plumbing vent pipes.

Those issues aside I'm not clear on what I'm supposed to do. We have the hood installed and we have a makeup air vent with some sort of powered damper. The thought is that it's supposed to open when somebody uses the hood. How do I make that happen?

According to a few websites there's supposed to be some low voltage terminals on the hood but I'll be darned if I can find them.

The model is electrolux rh36wc55gs, but the installation instructions don't mention it. The online instruction manual mentions it, but just says, "Local codes may require makeup air ducting."

 

[GoldDigger]

I just learned about this code from the 2009 IRC. For anybody who doesn't know, if you have an exhaust hood at a certain cfm (400, usually) that exhausts to the outside you must have a way to makeup the air pressure. Apparently they're worried about the hood drawing air through the chimneys and plumbing vent pipes.

Those issues aside I'm not clear on what I'm supposed to do. We have the hood installed and we have a makeup air vent with some sort of powered damper. The thought is that it's supposed to open when somebody uses the hood. How do I make that happen?

According to a few websites there's supposed to be some low voltage terminals on the hood but I'll be darned if I can find them.

The model is electrolux rh36wc55gs, but the installation instructions don't mention it. The online instruction manual mentions it, but just says, "Local codes may require makeup air ducting."

You could hook up the coil of a line voltage relay to the fan motor circuit so that the relay will pull in when the fan is on. The dry contacts that gives you can then be combined with low voltage transformer to provide the control current to a relay or motor on the damper. Another possibility that may meet the code requirement would be to just put in a barometric damper (one-way air flow valve) instead of a powered damper.

One reason that the installation instructions just mention the local (or global, for that matter) codes rather then telling you about the non-existent relay terminals is that, again, the code may require ducting, but not a powered damper.

 

[jaylectricity]

You could hook up the coil of a line voltage relay to the fan motor circuit so that the relay will pull in when the fan is on. The dry contacts that gives you can then be combined with low voltage transformer to provide the control current to a relay or motor on the damper. Another possibility that may meet the code requirement would be to just put in a barometric damper (one-way air flow valve) instead of a powered damper.

It just seems like a lot of to-do to mess with the manufacturer's wiring internally. I think they're already decided on the powered damper, or maybe this state requires it to be powered. Which seems dumb, since they'll be getting cold air pumped into their house while they're using the fan in January.

 

[GoldDigger]

It just seems like a lot of to-do to mess with the manufacturer's wiring internally. I think they're already decided on the powered damper, or maybe this state requires it to be powered. Which seems dumb, since they'll be getting cold air pumped into their house while they're using the fan in January.

A powered damper must means that the actuation of the damper is controllable. It does not mean that there is a fan there pushing cold air in. And, FWIW, I would much rather have a damper letting cold outside air in close to the hood so that it can go right out again than let the hood fan pull all of the nice heated air out of the house and throw it away.
Satisfactory results will depend on putting the makeup air duct discharge in the right place more than anything else. Clearly you do not want it venting into the living room.

If the hood has an internal switch for the fan, it will be hard to avoid modifying the internal wiring. Although I suppose you could mount an air flow activated switch in the outlet duct of the fan if you really want to keep it cleanly separated.

 

[masterinbama]

Gravity Damper.

 

[GoldDigger]

Gravity Damper.

Would not work. Gravity only sucks. :angel:

 

[texie]

I just learned about this code from the 2009 IRC. For anybody who doesn't know, if you have an exhaust hood at a certain cfm (400, usually) that exhausts to the outside you must have a way to makeup the air pressure. Apparently they're worried about the hood drawing air through the chimneys and plumbing vent pipes.

Those issues aside I'm not clear on what I'm supposed to do. We have the hood installed and we have a makeup air vent with some sort of powered damper. The thought is that it's supposed to open when somebody uses the hood. How do I make that happen?

According to a few websites there's supposed to be some low voltage terminals on the hood but I'll be darned if I can find them.

The model is electrolux rh36wc55gs, but the installation instructions don't mention it. The online instruction manual mentions it, but just says, "Local codes may require makeup air ducting."

I've done these using a current sensor from somebody like RIB or others. This way you don't have to modify the hood wiring and risk listing and other issues. Just wire it up as a whole 'nother system using the current switch as a trigger. I note you are in a cold climate (and this falls on the mechanical guy) so be advised that dumping cold air into the house in the winter can be a real problem without proper design of the make-up air system.

I might add that this issue amazes me when it comes up. You would think that the high end appliance manufactures of these hoods would be aware of not only the code, but the basics of air flow and sound air moving practices. Trust me, if you call, say GE Monogram or Viking, or you name it they are clueless. If they had a clue they would give you a set of dry contacts for this purpose. I once did a job in a home that the owner wanted an island with a large "pro-consumer" cook top. Since it was an island, the CFM required was so great that it sucked the fire right out of the fireplace the first winter night. This is what happens when you have a residential kitchen designer doing a job they have no business doing and they really need an engineer to design a proper system.

 

[jaylectricity]

Yeah, I don't know why there aren't some sort of control contacts within the hood that I could run some 16 or 18 gauge bell wire to.

 

[GoldDigger]

Yeah, I don't know why there aren't some sort of control contacts within the hood that I could run some 16 or 18 gauge bell wire to.

Probably because they could not get UL approval to make the dry contacts part of the same switch assembly and they did not want to spend the additional money for the relay.
(Not that it is exactly a cutthroat cost-sensitive market, of course.)

 

[masterinbama]

Would not work. Gravity only sucks. :angel:

They are used quite often on smoke evacuation systems. All you are doing is relieving the negative pressure.

 

[Wenty4]

Makeup air requirement

Makeup air requirement

The International Mechanical Code is where you will find this requirement:

505.2 Makeup air required. Exhaust hood systems capable of exhausting in excess of 400 cfm (0.19 m³/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

It does not have to fan forced but the louvers must, apparently, be mechanically operated

 

[gadfly56]

Tempered Air?

Tempered Air?

For commercial systems the temperature difference between the make up air and exhaust air can't be more than 10 F, capacity of the HVAC system permitting (IMC 2009 508.1.1).

 

[mwm1752]

Whats to say a gravity damper will not simultaneouly open when air is exhausted? Mechanically does not refer to power assisted. IMO

 

[HoosierSparky]

Residential

Residential

The International Mechanical Code is where you will find this requirement:

505.2 Makeup air required. Exhaust hood systems capable of exhausting in excess of 400 cfm (0.19 m³/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

It does not have to fan forced but the louvers must, apparently, be mechanically operated

The IMC is not relevent in this case. The building is under the IRC and as its own mechanical requirments. They are based on the IMC, but do not include ALL of the IMC. It is the same for Plumbing (IPC or UPC) and in our jurisdiction the NEC.

The only exception is when we review and inspect large (> 3500 sq ft) homes that want to use commercial kitchen equipment they have to get a variance due to the IRC specifically stating commercial equipment shall not be used in residences. We had a 77,000 sq ft "home" that wanted 2 commercial type kitchens. We allowed it, but those areas had to comply with IBC, IPC, IMC and NEC requirements instead of IRC. It is one of the few residences I've run across that had a grease interceptor installed in the motor court!

 

[jaylectricity]

We brainstormed with the HVAC guy and he said he could pick up a pressure switch that he
could install into the exhaust duct. I can mount a 24V transformer in the basement near the makeup duct and run 18-2 class 2 up to the the pressure switch which will end up being hidden by the trim from the vent hood.

No messing with the manufactured circuit board, what a relief.

 

[Gregg Harris]

We brainstormed with the HVAC guy and he said he could pick up a pressure switch that he
could install into the exhaust duct. I can mount a 24V transformer in the basement near the makeup duct and run 18-2 class 2 up to the the pressure switch which will end up being hidden by the trim from the vent hood.

No messing with the manufactured circuit board, what a relief.

Think about that thought carefully. A pressure switch in the exhaust will be exsposed to grease.

 

[jaylectricity]

Think about that thought carefully. A pressure switch in the exhaust will be exsposed to grease.

Good catch. How long will the switch last before they have to pay somebody to replace it? Or if the building inspector would even allow it.

 

[mwm1752]

The IMC is not relevent in this case. The building is under the IRC and as its own mechanical requirments. They are based on the IMC, but do not include ALL of the IMC. It is the same for Plumbing (IPC or UPC) and in our jurisdiction the NEC.

The only exception is when we review and inspect large (> 3500 sq ft) homes that want to use commercial kitchen equipment they have to get a variance due to the IRC specifically stating commercial equipment shall not be used in residences. We had a 77,000 sq ft "home" that wanted 2 commercial type kitchens. We allowed it, but those areas had to comply with IBC, IPC, IMC and NEC requirements instead of IRC. It is one of the few residences I've run across that had a grease interceptor installed in the motor court!

Same Guide lines
2009 IRC
M1503.4 Makeup air required. Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

 

[Gregg Harris]

Good catch. How long will the switch last before they have to pay somebody to replace it? Or if the building inspector would even allow it.

Try a current sensing relay

 

[mgookin]

How do you get 400cfm coming in without a fan on the inlet?