Range Hood Interlock

[Mongo1953]

Hi all;

I have been asked by a client to interlock a built in microwave/range hood unit with the NG forced air heating system. Haven't run into this before and not sure how to approach it. Any advice/guidance would be appreciated.

 

[benaround]

If the hood fan pulls too much heat out of the house, the regular t-stat should turn the

heat on ? I think the best interlock would be for them to turn up the t-stat before using

the hood fan. jmo

 

[480sparky]

Hi all;

I have been asked by a client to interlock a built in microwave/range hood unit with the NG forced air heating system. Haven't run into this before and not sure how to approach it. Any advice/guidance would be appreciated.

When the micro hood ____________, the furnace should __________.

(Fill in the blanks)

 

[ultramegabob]

I dont really understand the advantage of what they are wanting to do, why not just leave the thermostat alone and let it turn the heat on when the temperature drops enough? having the furnace kick on with the hood will call for the furnace to kick on no matter what the temperature is in the room.

 

[augie47]

"customer wants a blue suit, turn on the blue light". Forget his reason, if he pays....add a relay to the hood fan and "break" the appropriate thermostat wire

 

[ultramegabob]

"customer wants a blue suit, turn on the blue light". Forget his reason, if he pays....add a relay to the hood fan and "break" the appropriate thermostat wire

I dont normally blindly do everything a customer wants, many times with a couple of questions I may come up with somthing that would work better. in this case if the temperature drops in the kitchen and if the thermostat is far away to kick the furnace on in a reasonable amount of time a second thermostat in the kitchen may do what they want.

 

[Mongo1953]

Hi, all;

In answer to 480 Sparky's reply, When the micro hood is exhaustingthe furnace should not fire. I think the reason for the request is to prevent the range hood fan from creating a negative air pressure condition that will cause a back draft down the chimneys of the natural gas furnace and hwt. The house is an older home with a standard furnace. (combustion air from the inside of the house)

I have no personal experience with this type of setup, but found a few vague references on Google. No details, though. Thought someone here at the forum with more experience or knowledge would be able to add some details as to where to find guidelines or standards for such an installation.

I am not going to do this installation unless I get this clarified as I am concerned that I may inadvertently create a safety hazard or code violation.

 

[480sparky]

Hi, all;

In answer to 480 Sparky's reply, When the micro hood is exhaustingthe furnace should not fire. I think the reason for the request is to prevent the range hood fan from creating a negative air pressure condition that will cause a back draft down the chimneys of the natural gas furnace and hwt. ...........

Sounds like the HO is trying to engineer a solution to a problem that most likely does not exist. Things might get mighty cold when cooking for the whole family next Thanksgiving........

Are they wanting the same set-up with the bathroom exhaust fans as well?

 

[ultramegabob]

A microwave/range exhaust hood isnt going to draw enough air to be an issue, they dont move anywhere near the air of a commercial kitchen hood that requires a make up air, I have worked in restaurants that the makeup air stopped working, and you could hardly open the front door due to the negative pressure in the building. If the they are having issues with the microwave hood sucking exhaust back into the house they have some other issues with their furnace, as stated before, you would have issues with the bath fans and the clothes dryer also.

 

[augie47]

or............... he's working for an engineer :grin:

 

[One-eyed Jack]

A microwave/range exhaust hood isnt going to draw enough air to be an issue, they dont move anywhere near the air of a commercial kitchen hood that requires a make up air, I have worked in restaurants that the makeup air stopped working, and you could hardly open the front door due to the negative pressure in the building. If the they are having issues with the microwave hood sucking exhaust back into the house they have some other issues with their furnace, as stated before, you would have issues with the bath fans and the clothes dryer also.

I agree with that. The gas appliances are required to have air for combustion and ventilation at or near the appliance. That micro hood fan wont have an impact if this is provided. If this problem exists "it" needs to be addressed first.

 

[Jljohnson]

"If" your microwave hood is on a dedicated circuit and "If" your furnace is as well, then this could be accomplished very simply adjacent to the electrical panel by using a current sensing relay on the micro feed and routing the furnace circuit through the dry contacts of the CSR. This could have negative impacts as well though, such as the central air conditioning, if installed, will not work when the hood fan is operated, and the real big one...the furnace would not operate while your microwaving popcorn. Now that I think about it the CSR is a horrible idea, unless you just route the heating wires from the thermost through the dry contacts and leave the furnace circuit alone. The CSR would need to be installed on the exhaust fan motor leads only, not the entire microwave, in order for this to work properly and not have the negative impacts as mentioned.

 

[electricmanscott]

or............... he's working for an engineer :grin:

Funny, that's what I thought too. :grin:

 

[benaround]

Mongo,

Turning off the furnace could do what they want, but, I think the better way to do it

would be leave the furnace like it is and add an outside air damper interlocked with the

hood. This way would allow the heat to function without any 'back drafted flues' causing

problems.

It would not cost too much to install a 'sail switch' in the hoods exhaust duct for the

control.

 

[SAC]

or............... he's working for an engineer :grin:

Funny, that's what I thought too. :grin:

Ahhh, so someone found out that we get to do whatever we feel like for no reason whatsoever? Well why else would someone be an engineer? But remember that it's real hard work and lots of hours and most fail out of school anyway because its a nightmare so don't become an engineer and leave it all to us and you just don't understand anyway.

And by the way, the right solution here most obviously requires optocouplers...

 

[kwired]

better idea yet is to get combustion air from outside to the furnace will probably cost the least and require the least maintenance. How long until this older furnace needs replaced. New one will probably need intake anyhow.

 

[benaround]

better idea yet is to get combustion air from outside to the furnace will probably cost the least and require the least maintenance. How long until this older furnace needs replaced. New one will probably need intake anyhow.

Yeah, but what about the optocouplers ?

 

[Mongo1953]

Thanks for all the feedback, all. I am meeting with the gc tomorrow morning to seal the deal on this project and I will be able to discuss his request a little more intelligently thanks to your input. He seems to be mistaken in thinking he needs this done.

This forum is one of the most helpful and entertaining resources I have found since starting my business. When I am even a little unsure, I check here first.

Thanks again, all.