# Make up air transfer grills?



## beenthere (Mar 5, 2009)

Not make up air, combustion air. In the code books, they are 2 entirely different things.

Good thing the OP is from NJ.


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## The Coastal Craftsman (Jun 29, 2009)

beenthere said:


> Not make up air, combustion air. In the code books, they are 2 entirely different things.
> 
> Good thing the OP is from NJ.


They may be called different things but they are in reality the same things. Put a glass over a match and see what happens, put your hand over the air intake on your vehicle and see what happens. These appliances all need air no matter if they burn that air or not. I get most houses will have enough leakage to allow more air to make it's way in but when you do what I have done and sealed up every gap i can find to save on heating costs these issues show their ugly heads. It's the reason I have 3 carbon monoxide alarms and sensors in my furnace room alone. If I didn't have the experience I had from corgi in the UK I prob wouldn't worry about it but when I seen what happens when new air is not allowed to enter the building when the boiler or fire is running it's not hard then to be concerned about it. I doubt the US is that far away from being as strict as the UK on this topic. These high efficiency condensing boilers and furnaces don't have these problems because of the concentric vents but many people still use direct vent furnace and water heaters.


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## flashheatingand (May 3, 2008)

And, that's a good reason why to let the house breathe a little. Heck, if you can't afford to pay your utility bills, you have too much house in the first place.


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## The Coastal Craftsman (Jun 29, 2009)

flashheatingand said:


> And, that's a good reason why to let the house breathe a little. Heck, if you can't afford to pay your utility bills, you have too much house in the first place.


Your right but I'm too tight to by a new furnace and AC and the house is in need of one so I'm doing what I can to keep the cool air and hot air in :laughing:


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## beenthere (Mar 5, 2009)

BCConstruction said:


> They may be called different things but they are in reality the same things. Put a glass over a match and see what happens, put your hand over the air intake on your vehicle and see what happens. These appliances all need air no matter if they burn that air or not. I get most houses will have enough leakage to allow more air to make it's way in but when you do what I have done and sealed up every gap i can find to save on heating costs these issues show their ugly heads. It's the reason I have 3 carbon monoxide alarms and sensors in my furnace room alone. If I didn't have the experience I had from corgi in the UK I prob wouldn't worry about it but when I seen what happens when new air is not allowed to enter the building when the boiler or fire is running it's not hard then to be concerned about it. I doubt the US is that far away from being as strict as the UK on this topic. These high efficiency condensing boilers and furnaces don't have these problems because of the concentric vents but many people still use direct vent furnace and water heaters.


Most likely. The CO detectors you have. Are the wrong ones. If they aren't low level. they aren't going to warn you of the real danger until the CO is too high.


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## The Coastal Craftsman (Jun 29, 2009)

beenthere said:


> Most likely. The CO detectors you have. Are the wrong ones. If they aren't low level. they aren't going to warn you of the real danger until the CO is too high.


I have a few different ones. The most accurate is a digital one that tells me the PPM down to 1PPM. I can't remember what is set to go of at though. I should check that. The others are just generic smoke/carbon monoxide detectors.


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## builderfalmouth (Nov 16, 2016)

flashheatingand said:


> And, that's a good reason why to let the house breathe a little. Heck, if you can't afford to pay your utility bills, you have too much house in the first place.


Never a truer word said!


Builders and Electricians


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## GAN57 (Sep 12, 2017)

flashheatingand said:


> Should be about 100 square inches. Is it feasible to bring in combustion air from the outdoors?


Transfer grill are rated 1 square inch per 1,000 BTU input. Metal grills only 75% of the total area is considered to be open (grates block space). Interior air one properly sized pass through within 12" of the ceiling and one the same size within 12" of the floor.

I viewed a later comment on sealed homes. A few things there. In the IECC any home that has less than 5 air exchanges an hour must provide "whole house ventilation". Anyone remember homes sealed tight in the 1970's? Air quality drops mold occurs.

Current 2015 IECC Northern U.S. requires no more than 3 air exchanges an hour. This is equal to a solid 1,700 sq. ft. block of plastic with a 12" x 12" hole cut into it open all the time. Continuous duty bath fans running about 75cfm 24-7, Ducted dampened intakes into the return air running 10-15 minutes every 12 hours or so for an air exchange or HRV installation.

Controlling the air leakage, gets over the need to overkill the HVAC requirements needed to overcome the 20 mile an hour wind when it is 5 below zero outside. Building Science.

You get into State like Illinois where I am, it is a "public act" that all new homes comply with the Energy Code.


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## greg24k (May 19, 2007)

2-12x12 grills top and bottom. 1sq/In = 1000 BTU. Lower opening within 12" of the floor, upper opening within 12" of the ceiling.


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## Fouthgeneration (Jan 7, 2014)

plumb cold air intake pipe to outdoors, stop using conditioned air as combustion air...

Install rat screens at both ends,and place as close to burner as possible. intakes well above any possible snow drift etc....

Then you close the make up vents and seal doors as tight as possible, the mechanical room thus being OUTSIDE air wise.


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## Big Johnson (Jun 2, 2017)

Fouthgeneration said:


> plumb cold air intake pipe to outdoors, stop using conditioned air as combustion air...
> 
> Install rat screens at both ends,and place as close to burner as possible. intakes well above any possible snow drift etc....
> 
> Then you close the make up vents and seal doors as tight as possible, the mechanical room thus being OUTSIDE air wise.


The only time I've seen a water heater plumbed for outside combustion air was big On-demand units. Do they make tank type that plumb to outside air too?


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## Fouthgeneration (Jan 7, 2014)

As houses tighten up and burners get smaller on home furnaces, conditioned air consumed by 30 and 40K Btu input rated hot water heaters and stoves become more important in maintaining a non- negative draft condition that could create a back draft of CO2 and Carbon monoxide gases inside our homes.... most HO select furnaces that REQUIRE out side air piping, thus leaving the HW heater as the largest "thief" of air pressure and O2 in our homes

Run a 50 % oversized pipe for the furnace into the mech room, use the room as a plenum for dividing the make up air....

many up scale homes use TWO medium hot water heaters as they often are cheaper and can often reduce hot water delays and to fill Jacuzzi style fixtures....

The various codes are dated minimum requirements IMHO

The original poster can install the remodel using internal only vents, but what happens when two fart fans or a range top vent and dryer run at the same time the furnace and HW heater are in operation?:blink:

Common sense also tells us that few if any basement levels ever have the air exchange numbers of their upstairs neighbors


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## GAN57 (Sep 12, 2017)

Fouthgeneration said:


> plumb cold air intake pipe to outdoors, stop using conditioned air as combustion air...
> 
> Install rat screens at both ends,and place as close to burner as possible. intakes well above any possible snow drift etc....
> 
> Then you close the make up vents and seal doors as tight as possible, the mechanical room thus being OUTSIDE air wise.



Good resolution buts works against the current Energy Codes. Unless as you stated you make this room isolated from the interior completely with insulated walls and an entry door.

In Illinois the 2015 IECC is a public mandate. This has a mandatory maximum of 5 air exchanges per hours (regular code is 3 for our region, Illinois allowed for the increase). So even at 5 AIH the dwelling is required to have whole house air. So unless you system (furnace or WH) is a direct vent types cutting holes to the exterior would create a possible violation. Granted this is for new construction.


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## Fouthgeneration (Jan 7, 2014)

Common Sense would have preventing exposure to CO and CO2 as MORE important than having less then 5 air exchanges /hour...:whistling

the volumes consumed are mathematically a small fraction of whole house Cubic Feet, # a few hundred Cubic feet of air an hour for both a HE furnace and HW heater.
Properly sized and installed outside combustion air venting REDUCES the number of ACHs in the living volumes..... Saves $ and increases lifetimes of its owners....

So Direct Vent exhausts/intakes are out of code compliance?

doesn't every straw stuck in the balloon of the home's skin require more available make up air? 

Ever tightening air exchange standards are going create a nation wide train wreck as oxygen using appliances use an ever greater % of available Air from inside the Tents of Eco- Nuttery


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## GAN57 (Sep 12, 2017)

There is no real common sense in codes as your aware.

No "direct venting' is in complete compliance as the exchange is completely sealed. Better for all, less dust, better overall interior air quality.

Even some on demand water heaters are direct vent, with the most of them needed to be adjacent to an exterior wall. Or as I am seeing in some new construction instances going electric or geo-thermal.

The air exchanges have a more direct correlation with the need to "oversize" heating & cooling equipment to deal with the 50MPH winds when 5 or 10 below zero or when 105 degree temps require severe oversizing.

Controlling air exchanges from 9 or 10 per hour as in previous years, getting it closer to zero and controlling it keeps the sizing requirements at a better balance. Since we all know and have heard the argument that we seal a house up tight and get mold growth or seal it and cut holes in it.

The best explanation I heard was at a seminar several years ago where the speaker was an ex-NASA scientist who had spent the previous years up in Canada practicing "building sciences". Imagine a 2,000 sq. ft. home made out of a solid block of plastic, then imagine it magically hollowed out. Know cut a 16" x 16" hole in it open 24-7 365 days a year. That equates to app 5 air exchanges per hour. A 12" x 12" hole is near 3 air exchanges an hour. Now control it with a continuous duty bath fan running about 75cfm 24 hours a day this does the air exchange. Ducted and electronically dampened runs to the return air timed to exchange X amount of cubic feet of air per 4 hour or 6 hour running. High end would be an HRV.

We are seeing decent air quality, no mold and power bills in Midwest of $150.00 to $175.00 per month. 

In essence your controlling it with a science, instead of let it pour in, when Manual J & D's are used as well as energy codes, commissioning of equipment, blower door tests (which are mandated under the energy code).

I know it took me 6 years or so of getting over the old assumptions to see how it works in real life, when done correctly. It is just the absolute newest building science which some of us old timers aren't used to.


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## chimneymantom (Oct 27, 2017)

*I just had this conversation*

Thanks everyone for laying all this info out here like this. Working with a friend we've stumbled up this need and question. I appreciate this!


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## Rio (Oct 13, 2009)

Either this months or last months JLC had an interesting article on a hybrid ERV system that this company is using, might be worth taking a look at.


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## PlumbersDenver (Aug 12, 2016)

Have you considered the EVR strategy?


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