Caulking Basement where the floor meets the wall

[Not_Handy]

All,

I have a issue with my hot water heater occasionally back drafting. It happens when my range hood is on over my oven and when my AC is running as the fan in the furnace blowing must pull in air. I notice when I open a window in the basement and allow air into the basement it stops the issue. Therefore, something is causing my basement to be in need of additional air. I also have a randon system which has a fan that pulls air. I used smoke and can see a area in my basement where the floor meets the wall there is a crack that runs about 10 feet long and maybe a 1/8th to a 1/4 inch wide. The radon fan is pull air down through this crack as the smoke gets pulled into this crack. I wonder if this is contributing to the air being lost in my basement.

Therefore, should I caulk this area? If so, which type of caulk do you recommend. I am anal so I don't want toxic caulking in my basement of which I spend a lot of time in. Don't want the horrible smell or toxic chemicals.

Any recommendations on how to safely seal this crack would be appreciated.

[STEVEusaPA]

Don't caulk that crack! You already stumbled onto the solution...

I notice when I open a window in the basement and allow air into the basement it stops the issue. Therefore, something is causing my basement to be in need of additional air.

The radon affects the draft, the range hood affects the draft. You need to provide combustion air from the outside to your hot water heater...and your furnace if it is gas/oil.

There are a couple of ways, and a qualified HVAC person will know what's best.

[Not_Handy]

I hear you but do you think by sealing the crack in my basement which allows the radon to suck air down will potentially eliminate the need to provide combustion air from the outside.

when you say don't seal the crack, can you let me know why?

Addiontally, I never had this issue until I got a new furnace. the furnace use to share the same 5 inch chimey as water heater. Now it is only the water heater using that 5inch chemney. I was also told by putting a 3 inch liner in the chemey it could fix it.

[HVAC_Marc]

You have 2 issues -

One - seal the crack. This is imperative for a radon system
Two - add a make up air supply from the outdoors. It is needed for combustion air and for equalizing house internal air pressures when things such as fans are utilized. If you live in a humid climate, special equipment may be needed to help with the air exchange.

There are experts in this area which will likely chime in later.

[Not_Handy]

Thanks for the info. Really good information here. I have one person telling me not to seal the crack but another telling me to do so. I would think if it causing air to leave my basement it would be logical to seal it. What do you recommend I seal it with.

Plus some additional information that I did not know before my original post. My furnace which sits next to the water heater...... where the return air thingy runs into the filter they have 324A tape to seal any gaps. BUT underneath there is a gap without tape and sure enough this gap is pulling in air. Again this is underneath and near my hot water heater. Is it possible this is also contributing to it!

Again this is underneath, Any reason I cant seal this gap with 324A tape? Where the return duct meets to place where the filter sits

I have air return, then filter, then furnace. Underneath where the air return meets the filter area and where the filter area meets the furnace there is a slight gap sucking in air. Should I seal these with 324A tape like they did everywhere else but under?

The water heater sits right next to this....if there is a strong flow of air underneath getting sucked in I think it would affect my water heater draft.

[HVAC_Marc]

A radon system requires the top, uppermost barrier to be sealed. This is because you want the maximum amount of lower pressure beneath the barrier so that the maximum amount of radon is removed by the fan. Outdoor silicone, mortar mix for large holes and gaps, or mastic can fill these areas.

The holes you have in the duct system are not readily contributing to your air infiltration problem, but, they should be sealed for best system operation. Tape may not be the best option for a very large gap. Consult your HVAC man on that.

The problems you are having are when the radon fan, the ventilation fans, and (if applicable) the furnace combustion air are used. The air is removed from the home creating a negative pressure. Air has to come from someplace outside to equalize this pressure and the easiest way is the straight run down the hot water tank flue pipe.

A mechanical air exchanger/HRV can be installed to help mitigate the problem while maintaining the heat/cool/humidity in the house. The guy you need to consult here is TeddyBear. He's the all around know it all on these things.

[Not_Handy]

thanks for the reply, just trying to play devils advocate here.......you say the holes in my duct system are not readily contributing to my air infiltration problem. However, it is sucking in air a lot of air. Thus removing air from my basement. How is that not contributing to the negative pressure?

As for the tape not being the best option that is what the installs used to seal the other gaps. They just didn't do the bottom. Probably because its not visible as the customer won't see.

I can use outdoor silicone?

[Not_Handy]

also the radon company that installed my unit said they only caulk/seal gaps bigger than 1/4th an inch.

I have been using a ensense stick for smoke to figure out draft flow, anyone have any other tips on creating smoke or a device one can buy?

[HVAC_Marc]

thanks for the reply, just trying to play devils advocate here.......you say the holes in my duct system are not readily contributing to my air infiltration problem. However, it is sucking in air a lot of air. Thus removing air from my basement. How is that not contributing to the negative pressure?

As for the tape not being the best option that is what the installs used to seal the other gaps. They just didn't do the bottom. Probably because its not visible as the customer won't see.

I can use outdoor silicone?

Yes, use outdoor silicone. it is the most resilient to stretching and abuse.

unless the holes in your duct system are removing air from the house, they are not contributing to the hot water tank problem.
the air removed from the cellar (now negative pressure) is pushed to the upstairs (now positive). The positive flows to the negative under doors or by other means. Its net effect is zero.

Your ventilation fans or furnace venting are the problems.

the tape is really designed for very small gaps. Anything a 1/4 inch or larger should be sealed with metal.

[Not_Handy]

thanks very much for your insight. Ive learned more from this forum then the so called pros that have visited my house.

Can you be more specific on the silicone. Like recommend a brand? Is it possible if I fill this gap causing air to leave the basement via the randon fan this will help my neg pressure?

also, I get you what you saying it has net zero effect. However, the water heater is a few feet away from the furnace which is pulling in a lot of air from the bottom. I would think that would affect draft.

what is ventilation fans or furnace venting?

[Not_Handy]

not sure if my gap is less than 1/4th or not and not sure how they would even use metal in this situation. If I use tape and its about 1/4th a inch what is the consequence

[HVAC_Marc]

ventilation fans - radon fan, bathroom fan, stove/oven fan, dryer

furnace venting - combustion air that is drawn from the house and pushed to the outdoors via a powered fan or by natural process

using tape across large gaps will work for a short time, until the glue dries out or the pressure of the air on the tape collapses it into the space it is trying to cover. It may get pushed into moving or electrical parts inside the furnace causing more damage. An HVAC guy would disassemble the ducts, rebuild what is needed, and put it all back together.

Any kind of outdoor silicone would be fine, GE, DAP. Make sure you get the type that CANNOT be painted over and is NOT water cleanup.

Sealing the cracks and holes in the floor will not remove the negative pressure problem. It will make your radon system function as intended and is required for your safety.

If your hot water tank is running, but backdrafting because of negative pressure, and your furnace blower is running pulling air in from the floor area (due to bad duct construction), it is pulling in combustion byproducts and pushing them into the home. In this situation, it is LIKELY that there is carbon monoxide (CO) in the air stream.

[Not_Handy]

I highly appreciate the information but o great make me even more paranoid. CO in the air system, just wonderful.

I have multiple CO detectors and none of which are showing any CO

I have GE silicone 2 for the crack?

[vstech]

I highly appreciate the information but o great make me even more paranoid. CO in the air system, just wonderful.

I have multiple CO detectors and none of which are showing any CO

I have GE silicone 2 for the crack?

Store bought CO detectors only react when the CO levels in the house exceed immediate deadly levels... CO is a blood poison that can and will accumulate in the blood from low levels below the detectors ability, and kill. VERY few detectors are rated to detect low levels.

[vstech]

Any of the pure silicone caulks will work, don't use the ones with acrylic or paintable caulks.

[Not_Handy]

Store bought CO detectors only react when the CO levels in the house exceed immediate deadly levels... CO is a blood poison that can and will accumulate in the blood from low levels below the detectors ability, and kill. VERY few detectors are rated to detect low levels.

I have 5 in the house. 4 of which read levels in the teens and have a peak level button. So you saying these are pointless? Should I just chuck them In the trash.

[Not_Handy]

ventilation fans - radon fan, bathroom fan, stove/oven fan, dryer



Sealing the cracks and holes in the floor will not remove the negative pressure problem. It will make your radon system function as intended and is required for your safety.

.

if the radon system is pulling air from the living area in the basement and removing it from the house how is that NOT contributing to negative pressure?

[HVAC_Marc]

it is contributing to the problem. Sealing the cracks will make the problem worse, but will make your radon system work as it's supposed to.

as above, most UL listed CO detectors alarm when it's too late. I think the cutoff is 35 PPM.

[Not_Handy]

it is contributing to the problem. Sealing the cracks will make the problem worse, but will make your radon system work as it's supposed to.

as above, most UL listed CO detectors alarm when it's too late. I think the cutoff is 35 PPM.

I guess I should chuck the CO detectors out the window. They read levels below 30 even, how are they not somewhat useful. I do think you guys are very knowledgeable and I am learning a lot here. For that I'm grateful, but I do also feel like a lot of these comments are a bit on the fear side. Like saying CO detectors will only sound once dead, thus useless. I mean really?

How would sealing the cracks make the problem worse? Wouldn't it make the problem better by not allowing air from the basement to escape?

Also, this time of year the water heater is the only thing using gas as the heater obviously isn't on. So the water heater would be the one thing that could produce CO not the furnace this time of year. I mean how long would that pupply have to run to fill a 2,600 sq foot home enough to be deadly. The thing hardly ever runs to begin with. Plus I check it to make sure it is venting properly when it does until I get this figured out.

The other odd thing the city stuck a CO detector right where the air comes out of the water heater and it wasn't even reading CO so it must burn well.

[Shophound]

As others have said, you need makeup air to keep the house pressure neutral when the exhaust fans operate. All duct leakage should be sealed. As for gap in floor, if radon fan is cause of air moving into crack (and even if it is not), seal the crack.

You should get a pro with a blower door to perform worst case CAZ (combustion appliance zone) testing on your home after all sealing efforts and makeup air provision is in place.