Exhaust Fan-DuctWork Help

[jasoncw]

Thank you for this advice-good stuff. I always pictured my future tank in a dedicated fish room, with one big fan bringing air in from the outside, and another fan blowing air back to the outdoors. (Just for the fish room).

Two fans to keep things simple. This would also work yes?

The main issue I see with that is you will be pulling in freezing air in the winter and hot air in the summer.

 

[Fibinotchi]

Carbon monoxide, or CO, is a byproduct of incomplete combustion on natural gas, or propane appliances. It is not a concern on electric appliances. It also is a concern with fireplaces. If you have leaks to the exterior of your house in your supply ducts of your home and no leaks in the return air system, you can pull your home into negative pressure. If you have a large range hood fan or bath fans and your home is sealed up very tight, you can also pull your home into a negative pressure. If you pull your home into a vacuum of -6 pascals you can have a flame roll out on your gas appliances, or can cause the appliances to not vent to outside which can cause co poisoning. Not very common from exhaust fans.

 

[kcress]

Also - what sort of dangerous gases can build up in the house? I can think of CO2 buildup from exhaling our own breath. But other than that? This home is from the 1950s. Just a basic furnace in the basement, stove up in the kitchen. I'd like to know more about this just to learn what appliances can cause these gases.
Thanks!

It's the same problem available in most every house, furnaces, water heaters, and fireplaces which all exhaust poison gas CO. They exhaust it, usually thru the process of draft. That process runs because the hot air leaving the appliance is less dense the the air surrounding the appliance and hence, floats. It floats up the associated stack and out thru the roof.

Draft by nature is not very strong.

Bring in a mechanical blower. A mechanical blower physically drives the air - not draft. When you have a sealed up house with all the windows and doors closed and you put a blower in that exhausts of-of-doors, it will cause the actual air pressure to drop in the house. Depending entirely on how powerful the blower is and how air-tight the house is, will determine how low the pressure in the house drops.

If it drops too low then the make-up air that has to get into the house to replace the air mechanically blown out of the house will overpower the "natural drafts" of your various draft operated appliances. The make-up air will rush down the various flues from outside. The result is that the combustion products get sucked into the house's living space and don't leave via the various stacks any longer. The make up air starts coming down the various stacks leaving no path for the combustion gases.

Normally this wouldn't actually cause a serious issue because theoretically the blower is causing a lot of air to be turning over in the house and good appliances don't make a lot of CO. It's rather like a fire in a teepee. Fresh air coming in and 'used' air now with some combustion products, leaving. However... Most appliances that use draft get rather disturbed when the draft has failed and find instead, a breeze coming DOWN the flue. This causes their burners to not work properly. The result is instead of clean burning with a tiny insignificant amount of CO being produced a huge amount is produced from the smokey wrong flames that now are occuring.

A secondary problem is that flue gases can be extremely hot, several hundred degrees. When they can't go up the flue they can stream out sideways and ignite anything around them. This is often called "roll-out". Furnaces are famous for it.

To sum it up. If your house has fuel fired appliances that operate on the draft principal you need to be careful about installing mechanical blowers.

You should just not do it if your house is really tight and you have draft appliances inside the living space. This would be older houses, as all new ones, place the draft appliances outside the living space with the exception of large gas cook stoves.

You still have to be very careful if your tank is associated with an attached garage because the rules call a garage a non-living space. But, you could put a large blower in the garage blowing out and have both a water heater and a furnace trying to draft out of that same air space into the garage.

If you have to put a blower in don't get carried away with its power. A bathroom fan is probably not going to be a big problem. Several of them - maybe.

Test your installation. On a calm day close every single window and door. If you have bathroom fans and/or kitchen hood fans run them now. This includes your dryer. You can just run it on air fluff so you don't waste extra energy.

Now run all the draft appliances at once. Find the areas where the burners mix room air with the combustion gas on entry into the stack. Light a match and hold it close to this gap. Look for any sign of ANY air flow out of this gap. It should always be moving towards the flue.. You can also blow the match out and watch the smoke. Use lots of matches. Be sure. The prevailing air flow must head with no hesitation towards the flue. Once you've scoped this out on all the appliances, with them all still running, turn ON your new blower. Repeat the tests at all your draft appliances. Does the air still flow towards the stacks in all cases? It better - or else you and yours are in mortal danger.

If this is beyond your abilities, and don't be ashamed if it is, have a reputable HVAC company come and check for safe draft conditions when using a newly installed blower that moves air from the living space to outside. They can run this same test or use more sophisticated equipment to provide the info.

 

[hvacman250]

Thank you for this advice-good stuff. I always pictured my future tank in a dedicated fish room, with one big fan bringing air in from the outside, and another fan blowing air back to the outdoors. (Just for the fish room).

Two fans to keep things simple. This would also work yes?


Also - what sort of dangerous gases can build up in the house? I can think of CO2 buildup from exhaling our own breath. But other than that? This home is from the 1950s. Just a basic furnace in the basement, stove up in the kitchen. I'd like to know more about this just to learn what appliances can cause these gases.

Thanks!

Totally agree with the quote below.

The main issue I see with that is you will be pulling in freezing air in the winter and hot air in the summer.

No house, especially a 50's house, is completely airtight. The CO2 you breath cant buildup unless you had 1000 people in the house, and then it still probably wouldnt be high enough to hurt anything.

The only other "dangerous" gas would be carbon Monoxide, which is from improper combustion. Only a gas burning appliance could emit that if something was wrong. Any house with a gas appliance should have a CO detector AND be checked regularly.

 

[hvacman250]

It's the same problem available in most every house, furnaces, water heaters, and fireplaces which all exhaust poison gas CO. They exhaust it, usually thru the process of draft. That process runs because the hot air leaving the appliance is less dense the the air surrounding the appliance and hence, floats. It floats up the associated stack and out thru the roof.

Draft by nature is not very strong.

Bring in a mechanical blower. A mechanical blower physically drives the air - not draft. When you have a sealed up house with all the windows and doors closed and you put a blower in that exhausts of-of-doors, it will cause the actual air pressure to drop in the house. Depending entirely on how powerful the blower is and how air-tight the house is, will determine how low the pressure in the house drops.

If it drops too low then the make-up air that has to get into the house to replace the air mechanically blown out of the house will overpower the "natural drafts" of your various draft operated appliances. The make-up air will rush down the various flues from outside. The result is that the combustion products get sucked into the house's living space and don't leave via the various stacks any longer. The make up air starts coming down the various stacks leaving no path for the combustion gases.

Normally this wouldn't actually cause a serious issue because theoretically the blower is causing a lot of air to be turning over in the house and good appliances don't make a lot of CO. It's rather like a fire in a teepee. Fresh air coming in and 'used' air now with some combustion products, leaving. However... Most appliances that use draft get rather disturbed when the draft has failed and find instead, a breeze coming DOWN the flue. This causes their burners to not work properly. The result is instead of clean burning with a tiny insignificant amount of CO being produced a huge amount is produced from the smokey wrong flames that now are occuring.

A secondary problem is that flue gases can be extremely hot, several hundred degrees. When they can't go up the flue they can stream out sideways and ignite anything around them. This is often called "roll-out". Furnaces are famous for it.

To sum it up. If your house has fuel fired appliances that operate on the draft principal you need to be careful about installing mechanical blowers.

You should just not do it if your house is really tight and you have draft appliances inside the living space. This would be older houses, as all new ones, place the draft appliances outside the living space with the exception of large gas cook stoves.

You still have to be very careful if your tank is associated with an attached garage because the rules call a garage a non-living space. But, you could put a large blower in the garage blowing out and have both a water heater and a furnace trying to draft out of that same air space into the garage.

If you have to put a blower in don't get carried away with its power. A bathroom fan is probably not going to be a big problem. Several of them - maybe.

Test your installation. On a calm day close every single window and door. If you have bathroom fans and/or kitchen hood fans run them now. This includes your dryer. You can just run it on air fluff so you don't waste extra energy.

Now run all the draft appliances at once. Find the areas where the burners mix room air with the combustion gas on entry into the stack. Light a match and hold it close to this gap. Look for any sign of ANY air flow out of this gap. It should always be moving towards the flue.. You can also blow the match out and watch the smoke. Use lots of matches. Be sure. The prevailing air flow must head with no hesitation towards the flue. Once you've scoped this out on all the appliances, with them all still running, turn ON your new blower. Repeat the tests at all your draft appliances. Does the air still flow towards the stacks in all cases? It better - or else you and yours are in mortal danger.

If this is beyond your abilities, and don't be ashamed if it is, have a reputable HVAC company come and check for safe draft conditions when using a newly installed blower that moves air from the living space to outside. They can run this same test or use more sophisticated equipment to provide the info.

Very well put. I'm too lazy to write that much.:lolspin:

Although he did say it was a 50's house. I'd be willing to bet its losing 50% of air per hour.

And most, if not all, furnaces since the 90's have a rollout switch around the burner area, sometimes up to 4 of them. If any flame rolls out, the furnace shuts off and has to be manually reset.

 

[on the spot]

Two fans to keep things simple. This would also work yes?

I'll have to look for it and I don't recall his screen name but someone did just that for cooling purposes. I believe it was posted on Michigan Reefers, but it might have been here.

I can't see needing two fans for humidity control though...unless you have two fans in the bathroom ceiling. I just have the one but my house is rather goofy.

****
fan thread is here.

 

[chatyak]

It's the same problem available in most every house, furnaces, water heaters, and fireplaces which all exhaust poison gas CO. They exhaust it, usually thru the process of draft. That process runs because the hot air leaving the appliance is less dense the the air surrounding the appliance and hence, floats. It floats up the associated stack and out thru the roof.

Draft by nature is not very strong.

Bring in a mechanical blower. A mechanical blower physically drives the air - not draft. When you have a sealed up house with all the windows and doors closed and you put a blower in that exhausts of-of-doors, it will cause the actual air pressure to drop in the house. Depending entirely on how powerful the blower is and how air-tight the house is, will determine how low the pressure in the house drops.

If it drops too low then the make-up air that has to get into the house to replace the air mechanically blown out of the house will overpower the "natural drafts" of your various draft operated appliances. The make-up air will rush down the various flues from outside. The result is that the combustion products get sucked into the house's living space and don't leave via the various stacks any longer. The make up air starts coming down the various stacks leaving no path for the combustion gases.

Normally this wouldn't actually cause a serious issue because theoretically the blower is causing a lot of air to be turning over in the house and good appliances don't make a lot of CO. It's rather like a fire in a teepee. Fresh air coming in and 'used' air now with some combustion products, leaving. However... Most appliances that use draft get rather disturbed when the draft has failed and find instead, a breeze coming DOWN the flue. This causes their burners to not work properly. The result is instead of clean burning with a tiny insignificant amount of CO being produced a huge amount is produced from the smokey wrong flames that now are occuring.

A secondary problem is that flue gases can be extremely hot, several hundred degrees. When they can't go up the flue they can stream out sideways and ignite anything around them. This is often called "roll-out". Furnaces are famous for it.

To sum it up. If your house has fuel fired appliances that operate on the draft principal you need to be careful about installing mechanical blowers.

You should just not do it if your house is really tight and you have draft appliances inside the living space. This would be older houses, as all new ones, place the draft appliances outside the living space with the exception of large gas cook stoves.

You still have to be very careful if your tank is associated with an attached garage because the rules call a garage a non-living space. But, you could put a large blower in the garage blowing out and have both a water heater and a furnace trying to draft out of that same air space into the garage.

If you have to put a blower in don't get carried away with its power. A bathroom fan is probably not going to be a big problem. Several of them - maybe.

Test your installation. On a calm day close every single window and door. If you have bathroom fans and/or kitchen hood fans run them now. This includes your dryer. You can just run it on air fluff so you don't waste extra energy.

Now run all the draft appliances at once. Find the areas where the burners mix room air with the combustion gas on entry into the stack. Light a match and hold it close to this gap. Look for any sign of ANY air flow out of this gap. It should always be moving towards the flue.. You can also blow the match out and watch the smoke. Use lots of matches. Be sure. The prevailing air flow must head with no hesitation towards the flue. Once you've scoped this out on all the appliances, with them all still running, turn ON your new blower. Repeat the tests at all your draft appliances. Does the air still flow towards the stacks in all cases? It better - or else you and yours are in mortal danger.

If this is beyond your abilities, and don't be ashamed if it is, have a reputable HVAC company come and check for safe draft conditions when using a newly installed blower that moves air from the living space to outside. They can run this same test or use more sophisticated equipment to provide the info.

Great post thank you. The only appliances we have are an electrical stove, furnace, water heater, microwave etc.. dryer and washer of course. I am planning to live in Texas in a few years and it will be my first home. Just trying to learn these things as I have zero experience with these types of issues.

Now if we say... have a window open in the house - would this counteract any sort of negative pressure/draft issues?

 

[kcress]

Great post thank you. The only appliances we have are an electrical stove, furnace, water heater, microwave etc.. dryer and washer of course. I am planning to live in Texas in a few years and it will be my first home. Just trying to learn these things as I have zero experience with these types of issues.

Now if we say... have a window open in the house - would this counteract any sort of negative pressure/draft issues?

All your appliances are electric?? If so none would have flue gasses so you should have no worries.

Certainly an open window would pretty much cancel any draft/blower issues. BUT! That is nothing you would ever want to base your safety on. A window could be closed by a guest, a storm, extreme cold, etc., etc. That's why any testing would require closing everything.