[ed3120]

I’m putting in a 660 CFM vent hood in my kitchen. There will be some bends in the output pipe, which I’ve read slow down the CFM of the air, so the output will likely be less than the 660 CFM, but I’m not sure by how much.

I’ve read that they recommend a makeup air hole for vent hoods above 400 CFM for the risks of negative pressure pulling carbon monoxide into the house for furnaces, etc.

My house has no chimney and has a both a direct vent furnace (forced hot air) and a direct vent water heater. Does the makeup air need apply to my house?

I’ll add that my house is not overly sealed/insulated and I consider it to be slightly drafty.

 

[Nealtw]

The air has to come from somewhere, so you will be making all those drafty areas worse as apposed to having a supply that you decide where the best place would be to bring air in.

 

[Missouri Bound]

I will assume you have a gas range and oven.
You won't be drawing any exhaust gases in from your furnace or water heater due to the way they are vented. Their air supply is taken care of.
But hours of cooking (with a gas appliance) will deplete oxygen and an exhaust fan will add to that. Some have installed vents into the cold air return that bring in outside air when a negative pressure starts to occur.
That being said, if you house is drafty as you suggest you will most likely be OK.
And you can always crack a window.

 

[Bud9051]

I don't think an exhaust fan contributes to depleting the o2. MB if you have a reference please post. The stove top or range may do so, but replacement air will come from somewhere.

It may just be terminology, but direct vent is not the same as sealed combustion. I think of direct vent as being a fan assisted exhaust and not certain that fan can deal with the monster you will be installing. Basically they would be working against each other and the stronger will win.

If they are indeed sealed combustion, then each would have its own intake air source, assuming the installer ran that to the outside. I've seen 2 where they did not.

Bud

 

[ed3120]

I don't think an exhaust fan contributes to depleting the o2. MB if you have a reference please post. The stove top or range may do so, but replacement air will come from somewhere.

It may just be terminology, but direct vent is not the same as sealed combustion. I think of direct vent as being a fan assisted exhaust and not certain that fan can deal with the monster you will be installing. Basically they would be working against each other and the stronger will win.

If they are indeed sealed combustion, then each would have its own intake air source, assuming the installer ran that to the outside. I've seen 2 where they did not.

Bud

Both the furnace and the water heater have dedicated exhaust pipes run to the outside. But the air intakes are just pulling from the basement room air.

 

[Missouri Bound]

I think you are correct about the direct vent aspect. The OP didn't mention sealed combustion but I took it as such. My mistake.
And my comment regarding exhaust fan.....I re-read my post and I must have been having a brain fart.
All in all....my last 2 sentences, given the information we tend to agree on, seem to be the most accurate.

 

[Bud9051]

Check both appliances and maybe talk to the mfg to see if they can be adapted to have an outside supply of combustion air. My oil fired furnace has a kit option, not familiar with gas furnaces or water heaters.

Bud

 

[u3b3rg33k]

I will assume you have a gas range and oven.
You won't be drawing any exhaust gases in from your furnace or water heater due to the way they are vented. Their air supply is taken care of.
But hours of cooking (with a gas appliance) will deplete oxygen and an exhaust fan will add to that. Some have installed vents into the cold air return that bring in outside air when a negative pressure starts to occur.
That being said, if you house is drafty as you suggest you will most likely be OK.
And you can always crack a window.

not really - that's the point. it's pretty easy to overcome the draft up a chimney in a tight house with a strong kitchen fan.

Both the furnace and the water heater have dedicated exhaust pipes run to the outside. But the air intakes are just pulling from the basement room air.

and the basement room air is coming from... ?

 

[Missouri Bound]

not really - that's the point. it's pretty easy to overcome the draft up a chimney in a tight house with a strong kitchen fan.

He doesn't have a chimney.

 

[Old Thomas]

You need makeup air for the for the furnace and water heater that are not using outside air for combustion. That is, unless you have a leaky house. Codes spell out how many square inches of inlet for each unit of BTUs.

 

[u3b3rg33k]

He doesn't have a chimney.

missed that. IF the installer didn't cheap out and you have supply air piped properly it might be OK.

 

[ed3120]

I will assume you have a gas range and oven.
You won't be drawing any exhaust gases in from your furnace or water heater due to the way they are vented. Their air supply is taken care of.
But hours of cooking (with a gas appliance) will deplete oxygen and an exhaust fan will add to that. Some have installed vents into the cold air return that bring in outside air when a negative pressure starts to occur.
That being said, if you house is drafty as you suggest you will most likely be OK.
And you can always crack a window.

not really - that's the point. it's pretty easy to overcome the draft up a chimney in a tight house with a strong kitchen fan.

Both the furnace and the water heater have dedicated exhaust pipes run to the outside. But the air intakes are just pulling from the basement room air.

and the basement room air is coming from... ?

Basement has a door separating it from the upstairs, but the door is usually open. I have a return vent on the main floor as well as one in the basement. Both returns run into each other and feed into the furnace/AC.

So if the basement is short on air it will pull from the upstairs either through the door or through the upstairs return sucking air in.

 

[Old Thomas]

Your makeup air is coming from upstairs. In a well sealed house, you can only suck a limited amount of air from a box. In reality your makeup air is coming from putting your living space under negative pressure forcing outside air in through every leaky spot. It would be better to put in a vent to allow your appliances to have makeup air directly from outdoors.

 

[beenthere]

Both the furnace and the water heater have dedicated exhaust pipes run to the outside. But the air intakes are just pulling from the basement room air.

They are not actually direct vent then.

It is a code requirement for make up air for hoods 600 CFM and above. Even in an all electric house.

 

[yuri]

Direct vent means the furnace and water heater have a exhaust fan which pushes the fumes out to the outside thru a pipe.

They have a pressure proving switch in the burner area which is supposed to prove there is enough air for safe combustion.

However that is tested under Normal house conditions which I imagine is with a range hood under 600 cfm.

Point is direct vent is a term BUT for safe clean proper combustion you need lots of combustion air and relying on a pressure switch for that is living very dangerously.

If you have sealed combustion then you have a intake and exhaust pipe ( 2 pipes ) going outside. Then your appliances won't be affected by a exhaust fan.

If you don't have a makeup air pipe then dirty outside air will be sucked in under your doors/around windows and can even be sucked thru electrical outlets on your wall and leave black stains.

 

[beenthere]

https://www.northlineexpress.com/b-vent-versus-direct-vent.html




Direct Vent

In direct-vent appliances, you use special direct-vent pipe recommended by the supplier. The direct-vent system involves two parts, one part for the exhaust and one for combustion air intake. The appliance itself is a completely sealed combustion chamber and no air from the house is used for combustion. The exhaust vents can go either out through a sidewall or through the roof.


https://hvacdirect.com/info/what-does-direct-vent-mean/


What Does Direct Vent Mean?


Direct-Vent Technology describes a gas burning appliance and how it uses two pipes, often one smaller pipe within another larger pipe, to both exhaust the appliances flue gases and bring in fresh air that it uses for combustion. They are one of the safest, most convenient, and most popular ways of adding a gas fireplace to your home. The area where the fire takes place, often called the combustion chamber, is sealed with a glass panel and gaskets that are protected by a safety barrier screen. This allows you to enjoy the view of the fire, prevents fumes from coming into the home, and prevents already heated room air from escaping out the chimney.

 

[yuri]

Yeah direct vent is a loose term. Fireplaces are a good example.

Just like draft inducer, ventor fan, inducer, combustion air inducer there are loose terms with several meanings.

Problem with the net is we need to see the exact setup and appliance and not all posters understand trade lingo and can describe their situation perfectly.

At the end of the the day it is not a great idea to exhaust huge amounts of air w/o bringing it back in in a safe controlled manner IMO.

 

[SPS-1]

How would the kitchen exhaust situation be effected if one has HRV ?

 

[Missouri Bound]

I did a bit of research regarding Broan vent hoods.
They manufacture an "Automatic Make Up Air Damper" that is connected to your furnace via the cold air plenum. It is wired to operate when the hood fan is on. From the plenum there is a damper that is vented outside. When make up air is needed the damper opens and allows outside air to replace the exhausted air.
It seems like it is the most straightforward way to bring in fresh air, condition it and satisfy any negative pressure issues.

 

[yuri]

How would the kitchen exhaust situation be effected if one has HRV ?

If the kitchen exhaust is running and removing huge amounts of air it can interfere with the HRV and unbalance it.

It can overload or slow down the HRV fan ( in theory ) and that will unbalance the airflow thru it and potentially cause it to freeze up in very cold climates.

That is if the HRV is taking stale air from vents open to the house. If it is sucking off the return duct only ( bypass setup ) then it may be OK.

My house uses open vents in the bathrooms and one in the kitchen/dining area. That would affect it if I had a huge exhaust fan. A HRV is usually 155 to 200 cfm.