Cooktop exhausts through thinwall tube though foundation. rainwater problem

[Odysseus]

I am a DIYer, so your kind patience appreciated. We just move into a new (to us) existing home which has a downdraft cooktop in the kitchen. The 4" downdraft exhaust goes down into the cabinet the space beneath, joins to a 6" thinwall PVC tube coming up from the foundation, then makes a tight(not sweep) 90 degree turn, then runs approx 30' through the foundation to the outside of the house and exhausts into a small casita about 8x10x10" and the floor of which is about 10" below grade. The outer wall of the little casita box is right against a sidewalk so there isn't room to make it larger.

When the inside of the tube is dry, the cooktop exhaust works just fine.

I must imagine that when the house was built, there must have been another elbow in the casita which turned up, then 90'd (or maybe even 180'd) above grade to keep the rain out. As it is now, the little casita fills up with water every time it rains. Unfortunately the tube through the foundation must be higher at the casita opening than just below the cooktop because the tube below the cooktop fills up with rainwater. I am guessing that if it doesn't rain for a really long time, that the water will eventually evaporate and the exhaust can then work normally.

I have pumped the water out once, built a 4" periscope PVC contraption to fit into the opening in the casita. There really isn't room to try to use solvent pvc glue and insert a 6" tube and elbow into the 6" thinwall, so I used a fairly tight fitting 6" rubber gasket/grommet/thingy I bought, around a 4" tube insert into the thinwall sealed with lots of exterior silicone caulk to keep water from entering the tube through the foundation. No cigar. Leaked like a sieve!

So plan B is to push a long 4" black corrugated plastic tube which I can buy at Home Depot all the way from the outside through the foundation and bring it up to the cabinet beneath the cooktop, and join it to the downdraft exhaust. Not sure I can push it given the 90 degree turn, so may have to run a fish wire and pull it through. At the outside it will turn tight enough to bring it straight up from the outlet in the casita, then turn it 180 degrees to keep rain out of the inside of it.

So question number one is will this maybe work or is it crazy and doomed from the start?

Second question is how to keep water out of the tube through the foundation (as I don't fancy the mold potential)? If I use Great Stuff (the low expansion one) around the corrugated tube at the opening (so there will be a 4" tube inside a 6" tube, held roughly centered by the expanding foam, will that keep water out of the tube? Atmospheric pressure is about 14 pounds so it seems like fairly low pressure pushing rainwater past the Great Stuff.

Whew! Thanks for any guidance and ideas you might have.

 

[FullySprinklered]

I don't know what a casita is. I'm out.

 

[Sponsor]

 

[Jadziedzic]

Using corrugated pipe is a bad idea for a couple of reasons: 1) it will greatly reduce the airflow through the exhaust so the downdraft vent fan may not be able to push sufficient air through the exhaust pipe, and 2) all the "stuff" emitted by the cooktop (grease, vapor, etc.) will quickly build up in the corrugations of the pipe. Can you get a 90 degree elbow and length of thinwall pipe (same diameter as the existing pipe) and glue that into the existing pipe with solvent cement so the new length of pipe extends a foot or so above ground, and maybe use a pair of elbows to route the pipe downward so rain, etc., don't wind up in the opening? Then fill in the ground around the new elbow.

 

[Odysseus]

A casita is a little box (literally a little house)

Very helpful guidance on the corrugated.

I am a bit timid about using PVC glue there. I have not found anything that slips into the 6" thinwall (actual interior diameter is approx 6.25 or 6.312 (can borrow a caliper if exact dimension helpful for this discussion). I fear that if I try to glue something that is not the correct O.D., I will wind up with an in place "obstruction" and since the 6" thinwall is encased in the concrete foundation, not sure how I would get back to where I was before trying that. Any thoughts you have on this are most welcome.

I believe there is a 4" flexible plastic hose/tube that that is "lined", i.e., smooth interior (can't remember the proper name for it) but don't know how flexible it is. May not go through the 90 degree elbow. Do you know of such a product?

 

[hj]

Using a 4" pipe on an exhaust system designed for a 6" pipe, may be a recipe for disaster. I was thinking it must be a very CRAMPED casita to be that small.

 

[Odysseus]

Using a 4" pipe on an exhaust system designed for a 6" pipe, may be a recipe for disaster. I was thinking it must be a very CRAMPED casita to be that small.

8 x 10 x 10". This home was built by a custom builder 26 years ago, but I am unsure if I would give them the benefit of the doubt with respect to "design" of the exhaust tube. In my mind a 4" exhaust emptying into a 6" thinwall is definitely preferred over 4" (either smoothwall or corrugated) all the way out.

The two points raised above: (1) "corrugated interferes with airflow"- agreed it is not optimal, but at least it is not blocked (by rainfall), and (2) will trap cooking particulates over time- agreed, but also pretty easy to replace as needed, and we don't use the exhaust very often.

I am very happy to use the setup as it exists IF I can figure out how to put a 90 degree into the existing thinwall exhaust tube that is watertight AND removable if need be in future (for cleanout or whatever).

Anyone have any ideas on any of this?

 

[CountryBumkin]

Could you abandon the under slab venting/pipe and run the vent up the wall to exit at roof?
My stove vent turns into a rectangular metal duct box in between the wall studs and runs through roof.
Is there a second story to your home?

 

[Odysseus]

Could you abandon the under slab venting/pipe and run the vent up the wall to exit at roof?
My stove vent turns into a rectangular metal duct box in between the wall studs and runs through roof.
Is there a second story to your home?

Thanks for the creative thinking. I could certainly do that, but at a huge multiple of costs, addition of tube shaft in 2nd story would be problematic, and there is a ceramic tile roof. That would be a distant last resort.

Want to try to solve the challenge with the existing if poss.

Is all 6" thinwall the same dimensions, especially I.D.? (Not sure even where the 6" comes from as I know the interior diameter is approx 6.25")

Edit: my final sentence prompted me to google for standard sizes, and OMG!. Here is what I found:

https://flexpvc.com/Reference/FullPVCPipeChart.shtml

The thinwall terminates about 1/2" inside the foundation wall so I am unable to reach it with the caliper, but these are my best estimates
OD: 6.559
wall thickness: 0.162 (fairly sure about this one)
ID: 6.316

The one that seems to fit best is CL 100 IPS SDR 41 (chart OD of 6.625, wall of 0.162, ID of 6.316)

Referring again to the chart, the only tube that seems able to slip into that tubing is SDR35 (chart OD of 6.275)

We are over my pay grade here, but assuming that both pipes are as clean as I can get them, would you imagine that the SDR35 would slip in and out of the SDR41 without binding so much that it might get stuck? If that is a risk (pretty close tolerances), would it be a bad idea to put a water soluble lubricant on it so that I can get it out as well as in?

If that is a good fit, recognizing that those dimensions are pretty close, and if I can build a periscope around the SDR35 to insert into the existing tube, insert the assembly with a generous amount of exterior silicone caulk around the join, then fill the casita (little box) with dirt, would you expect this to be watertight?

Thanks for your best guesses on this

 

[Odysseus]

In hopes that y'all haven't lost all interest in this, here's a couple more ideas:

A) build a concrete enclosure to replace the existing box, by which I can raise the opening 2 or 3" above grade (sufficient to keep pooling rainwater out). There would have to be a cover for the opening through which my "periscope" contraption would have to pass and be made watertight. If this is the better option, I will have several questions about building it.

B) [variation on A] dig out several inches beneath the bottom of the 6" tube (making the new concrete box deeper) and place a sump pump there. That way, assuming the sump pump can keep up with any rainfall, the water level shouldn't reach the tube and it should remain dry. This assumes that such a small "hole" would not be a foundation problem.

Any merit in these?

 

[Odysseus]

Efforts so far have fallen short, as water keeps getting back into the exhaust tube, so now ready to try a sump pump option.

I can think of two possible ways: One is to have a sump pump down in the elbow with an exhaust tube running the length of the existing pvc exhaust tube and dumping away from the exhaust box outside. I cannot tell what the floor of the elbow looks like or whether the low point is right at the bottom where the elbow is. So question one is what kind of pump is likely to be most effective given these unknowns? I don't know anything about sump pumps, so it would seem that one with a very low suction point would be most effective. Is there a pump that lays horizontally?

Two is what kind of float might be effective in this vague situation. Clearly it needs to cut off before the water level drops to the same level as the pump intake, and hopefully that water level will be low enough to clear the tube sufficiently for the cooker exhaust to function.

If anyone can form a picture from all of the above and send a photo or URL of a candidate pump, that would be helpful.

I don't know what the air temp of the exhaust gas will be, but likely pretty high, so what time of tubing for the pump exhaust should I use? (I am assuming that the pump will not have a heat issue, but that may be wishful thinking?)

Alternative two would be a pump in the cabinet beneath the cooktop with two tubes from the pump going into the down pvc tube, one short one to serve as water intake and the other (exhaust) going all the way to the outside. Same question regarding heat issues?

The advantage of this arrangement may be that, by fiddling with the intake tube, the water level may be able to be reduced lower than alternative one. The disadvantage is that it will need to be activated by a manual switch (unless a float might also work in this arrangement?)

Any thoughts appreciated (please remember I am a noob). Thanks

 

[hj]

quote; Atmospheric pressure is about 14 pounds

That is only a factor if you have a zero inch vacuum on the other side.

 

[Cacher_Chick]

You might want to read the installation instructions for the cooktop to see if PVC is even allowed for the appliance.
Not the same, but my experience with range hoods was that the fire code prohibits plastic piping.

 

[Odysseus]

hj, thank you for your reply but i have no idea what it means.

cacher_chick. I found an install manual:

https://jennair.com/digitalassets/JED4430WS/Installation_Instruction_EN.pdf

on page 6 it appears to me to confirm that PVC is acceptable. In any case that is how it was built so somehow I need to work with it. One thing that i took from the manual is that the downpipe may penetrate the slab and run under the foundation. If this is the case, then our central Texas soil movements could easily have damaged the thinwall tubing. If so, the water may be entering the 30' tube anywhere along its length.

Does anyone have any suggestions, ideas, or out-of-the-box solutions?

Thanks.

 

[Cacher_Chick]

The piping needs to be tested to see if it leaks. This could be done by sealing the ends and rigging up a test fitting to pressurize the pipe with air. With thinwall tubing, I would not exceed 1-2 psi, and a passing system should hold for at least 15 minutes. Another option would be to fill it with water to the highest level feasable to see if it will retain the water. If the piping system has integrity, then you should get by with installing a chimney cap or similar cover on the outer end to keep the rainwater out. I wonder too if condensation could not eventually fill the pipe also.

 

[Odysseus]

I have logged a lot of time trying to waterproof the system and have reached the limit of my ability, so now want to concentrate on getting the water out after each rain (not sure how the water gets in, but it happens after each rain.) Also it does not drain itself. The water just stays until I vacuum it out.

If I have a small pump (perhaps like a small fountain pump or maybe even a bigger fish tank pump) under the sink, will I have self-priming issues and if so, how might they be solved?

otherwise what type of pump might sit nicely in the elbow and act as a sump pump? If there is such, would I need to activate it manually or are there small pumps with float switches?

 

[Cacher_Chick]

I have logged a lot of time trying to waterproof the system and have reached the limit of my ability, so now want to concentrate on getting the water out after each rain (not sure how the water gets in, but it happens after each rain.) Also it does not drain itself. The water just stays until I vacuum it out.

If I have a small pump (perhaps like a small fountain pump or maybe even a bigger fish tank pump) under the sink, will I have self-priming issues and if so, how might they be solved?

otherwise what type of pump might sit nicely in the elbow and act as a sump pump? If there is such, would I need to activate it manually or are there small pumps with float switches?

You could use an automatic bilge pump made for a boat wired to a 12 VDC transformer. It would need to be in the lowest section of the pipe, where the water first begins to pool. In that environment where there could be oil or grease from cooking, I would not expect good long-term results.

As a matter of doing the right thing, a homeowner should take responsibility in having a proper repair done, even if the most viable solution is to get rid of the downdraft cooktop.

 

[Michael Young]

If the casita (never use that word again) is filling up with water - then answer the one question. What the hell does it do. Don't copy-cat a bad design. Get rid of the stupid thing and replace it with something that won't leak.

Where the pipe makes the penetration, slip two 4" ferncos around the pipe and use the ferncos to sleeve the pipe. Get rid of that 6" sleeve entirely. Get rid of the casita. Glue in a 4" 90 to bring it straight up and out. Flip a trap upside-down to keep rainwater from getting in. Pop a 4" rodent-proof cap o there. Seal the whole damn thing with concrete.

 

[Odysseus]

Thank you for this guidance, which please help me better understand.

Where the pipe makes the penetration, slip two 4" ferncos around the pipe and use the ferncos to sleeve the pipe. Get rid of that 6" sleeve entirely. Get rid of the casita. Glue in a 4" 90 to bring it straight up and out. Flip a trap upside-down to keep rainwater from getting in. Pop a 4" rodent-proof cap o there. Seal the whole damn thing with concrete.

The existing setup is a 4" cooktop downward exhaust joining the vertical 6" pvc tube, which takes a 90 degree turn about 18" below the join. I do not know whether the horizontal run from the 90 to the outside is encased in the slab or runs under it. By "penetration", are you assuming the latter, or to mean either?

If you are referring to the slab level (or below), there is nothing I am able to do there. If at the 4" to 6" join (which is accessible in the cabinet below the cooktop), I don't understand how to use the two ferncos. In any case there is no 6" sleeve, just a 30' horizontal run of 6" thinwall which 90 degrees upward to join the cooktop exhaust.

Any clarification/amplification appreciated.

 

[Storm rider]

We need to see pictures of the termination at the outside wall. Without that, we're all just guessing blindly.

 

[Michael Young]

Thank you for this guidance, which please help me better understand.



The existing setup is a 4" cooktop downward exhaust joining the vertical 6" pvc tube, which takes a 90 degree turn about 18" below the join. I do not know whether the horizontal run from the 90 to the outside is encased in the slab or runs under it. By "penetration", are you assuming the latter, or to mean either?

If you are referring to the slab level (or below), there is nothing I am able to do there. If at the 4" to 6" join (which is accessible in the cabinet below the cooktop), I don't understand how to use the two ferncos. In any case there is no 6" sleeve, just a 30' horizontal run of 6" thinwall which 90 degrees upward to join the cooktop exhaust.

Any clarification/amplification appreciated.

pics could help a lot