Smeg ksed72x can i vent into an existing chimney stack (approx 3m in height)

Good cheer, Bob.
GENERALLY speaking: on a direct vent water heater, meaning a passive air flow pipe up through roof, the vent stack should be higher than roof peak and should not have tree branches or any kind of living-space air intake (window, chimney) or air conditioner within 10 feet, or other exhaust nearby. Local codes affect exact location and height. For example areas with high wind might be different than other areas of country and require certain height, since the wind can stop combustion exhaust from exiting house, and topple over vent stacks, and push odorless poison CO gas into home where it will kill the parakeet and set off CO alarm.

This being said. Each model tankless can have different venting requirement.
I would contact Rinnai, and read installation manual, read the required maintenance, and make sure you have qualified service technician available in area to save posting on fixya next year.
Bosch has a pdf for testing proper draft on certain models: http://waterheatertimer.org/pdf/Bosch_Checking_the_draft.pdf

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

It the opening on the stove is on top of the stove, it's a 'B' vent. If the opening is in the back of the stove it's a "Direct Vent". However, some models have a connection on the back that's facing up,. A 90 degree elbow can be used to convert it to a horizontal run to enter an existing chimney, but then it must elbow up to connect to the pipe that is required to line the chimney. You should not just stop the pipe above the damper. It needs to run all the way to the top of the chimney, then have flashing seal the chimney's clay liner and a termination cap on the top.

here is a link to the Owners Manual/Installation Instructions for a Model 2600. It installs the same way as the 2610. http://homeappliance.manualsonline.com/mdownloads/62b85343-a800-4898-85a1-3d6d3c524259.pdf

Hope this helps you sort things out and do a proper installation.

If I understand correctly, your Bock gas water heater vent is causing water to leak down into chimney.
This is a very serious concern

Water leaking from water heater flue indicates improper venting.
The hot air gasses from water heater combustion contain water vapor, but the gas should vent out of house before condensate forms on pipes.
http://waterheatertimer.org/Water-at-bottom-of-water-heater.html#flue

The problem might be caused by a power vented furnace that pushes vent air from furnace down into flue pipe for water heater. As a result, the water heater doesn't vent properly.
There could also be a clog.
Light a match under water heater draft hood and see if smoke from match travels instantly upward.

There are two major concerns.
1) If vent is not working, it means that odorless CO gas is entering home instead of venting outdoors.
CO carbon monoxide is deadly poison.
http://en.wikipedia.org/wiki/CO_poisoning
This is a very serious concern
You can buy CO detector after vent is repaired.

2) Water condensate will eventually rust away vent pipes because of acidic content of the combustion vapor. It can be expensive to replace pipes, and pipes with holes pose risk of CO poisoning.

My suggestion is call a qualified plumber ASAP and explain what you observe.
Plumber will want to inspect the vent pipes, and may want to extend water heater vent pipe up further inside chimney so furnace is not pushing air back into water heater vent.
Plumber may also find blockage somewhere in the vent stack or chimney.
Also post on a professional water heater forum like the Tank to double check anything the plumber says to you. These are the pros.
http://www.thetankatwaterheaterrescue.com/forums/forum3/

Gas or electric?

1) Electric heater can be completely covered with insulation except TP valve. Set electric heater on insulated surface. Insulate pipes completely right down to tank.

2) Gas heater is different.
No insulation over combustion area, or gas valve, or air inlet or. No insulation on top of tank that will interfere with venting of dangerous combustion products including odorless CO gas. Foam insulation on pipes should stop 10" short of tank top. No insulation within 6" of the 3-4" inch galvanized vent pipe.

Here's photo with gas water heater insulation tips:
http://waterheatertimer.org/images/Insulate-gas-water-heater.jpg
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

3) Tankless gas. No insulation on box. No pipe insulation within 12". No insulation near vent pipe.

4) How much clearance between heater and chimney?? Not sure what that means. Is that the water heater vent stack? Or where vent stack goes into chimney stack? No insulation on gas flue pipes. Or within 6 inches of 3-4" water heater vent pipes

5) Is insulation fireproof? Everything burns if it's hot enough. If you throw insulation into backyard fire, paper and foil will burn away and insulation kind of falls apart in the heat. Fiberglass insulation cannot be set on fire with a match. Foam pipe insulation will burn.

look at the charts found in the NFPA 54 under venting. It will have a table based on btu load, height of chimney, length of pipe from heater to chimney and what temperature your area experiences. You can get this info on-line.

how do i plan to fix a chimney

you will have to place a straight edge on the top on the hood near the exhaust pipe then mesure from the floor to the bottom of the straight edge, that will give you depth then here is the demisons you have to build the box in. And if you don't have the power there you need to get a contrator or do it yourselfer to install it four you.

Price Range:£342 — £2,084 Average Price:£673 —— Colour body Stainless Steel. Body Material Stainless Steel. Colour chimney Stainless Steel. Typology Built-In. Motor location Integrated Motor. Operating Mode Convertible. Connection Rating (W) 225. Voltage (V) 230. Frequency (Hz) 50. Approval certificates IMQ. Length electrical supply cord (cm) 190. Height of the chimney (mm) 815/1970. Height of product, without chimney (mm) 815. Dimensions of the product, with chimney (if exists) (mm) 815-1970X898X490. Dimensions of the packed product...

is your return filter clean only last about 3 mo.is the coil plugged (Evap). or the freon is low. and check the condenser make sure it clean too.

Hello,

Here are the dimensions that relate to your cooker hood. The measurements are in mm.

Width 980 front 578 rear
Depth 480
Minimum height 1015
Maximum height 1170
Main canopy height 750
(excl chimney)
Chimney section width 436 main body/340 sliding section
Chimney section depth 170
Mounting height 650 - 750

Regards
Alan Hood
ami-man
Width 960 front, 578 rear Depth 480 Minimum height 1015 Maximum height 1170 Main canopy height (excl. chimney) 750 Chimney section width 436 main body / 340 sliding section Chimney section depth 170 Mounting height 650 - 750
Width 960 front, 578 rear Depth 480 Minimum height 1015 Maximum height 1170 Main canopy height (excl. chimney) 750 Chimney section width 436 main body / 340 sliding section Chimney section depth 170 Mounting height 650 - 750 Width 960 front, 578 rear Depth 480 Minimum height 1015 Maximum height 1170 Main canopy height (excl. chimney) 750 Chimney section width 436 main body / 340 sliding section Chimney section depth 170 Mounting height 650 - 750 Width 960 front, 578 rear Depth 480 Minimum height 1015 Maximum height 1170 Main canopy height (excl. chimney) 750 Chimney section width 436 main body / 340 sliding section Chimney section depth 170 Mounting height 650 - 750

Please check with your local building code for this information. Most inspectors will gladly answer your questions if you call them. You may be able to find the codes on local government web site too.

Check the manufactures recommendations as well. They should be in the box that the unit came in.