Can a furnace and water heater flue

[rmusa]

Can a furnace and water heater flue (92% eff) combine and go out side wall of basement? Final height about 36" above grade (washington, dc)

For a 92% eff furnace is concentric vent kit required? Can a regular 5" or 6" vent be used, with combustion air coming from inside the house.

What is minimum required installation height due to snow?

 

[PEDARRIN2]

Refer to International Fuel Gas Code, Chapter 5. Also, Appendix C has a good diagram of exit terminals.

In general, I do not like combining HVAC and Plumbing exhaust unless there is mechanisms in place to make sure the exhaust from one does not go the wrong way and end up in the other equipment, especially if you are bringing the combustion air from the room.

Since both of these are condensing type, you have to be careful about the venting materials due to low pH of the condensate. And regardless of what the manufacturer recommends, I would not use PVC for the exhaust.

 

[MikeHalloran]

I do not like combining HVAC and Plumbing exhaust unless there is mechanisms in place to make sure the exhaust from one does not go the wrong way and end up in the other equipment

There are no such mechanisms. They do not exist.
Mechanisms exist that LOOK LIKE they should work, e.g. check valves of various kinds.
They never work in actual practice for any usable length of time.
My experience is in multiple installations of combustion engines, where joining the exhausts looks like a great idea, until one of the engines is not running, and its cylinder liners are corroded enough to become unusable by the exhaust gases of the other engines, often in a matter of a few hours.
Similar concerns apply to parallel combustion systems that do not involve engines; just don't think about it.



Mike Halloran
Pembroke Pines, FL, USA

 

[PEDARRIN2]

MikeHalloran,

I may have to beg to differ.

We designed and specified an Exhausto system for a high rise hotel and convention center that tied the exhausts from the HVAC boilers and domestic water heaters. It was constructed in 2012.

I did not design it, but it was fairly intricate and have not heard of any operational issues.

 

[dbill74]

"Furnace"? As in used to heat air? If yes, then I would not. If the furnace is not operating during the summer, the chance of flue gases from the water heater going back into the house is too great.

Technically it can be done, you do need to ensure you avoid back feeding the appliances. Taking Mike's advice to avoid using a mechanical device, you would probably want to use induce draft.

Unless there is some compelling reason, avoid the trouble and run them separate.

You will never see concentric vent kits being "required". Codes merely "allow" them. I think you will be hard pressed to find anyone who prefers them over separate vent/flue.

Minimum height? See the fuel gas code and check local ordinances. Try also the local AHJ to see if they require heights different from what is in code.

 

[PEDARRIN2]

Since the water heater is 92% efficient, it is condensing and use of a concentric inlet/exhaust is common in commercial practice - not sure about residential since they can be a bit pricey.

Since this seems to be residential, i.e. house, I would also strongly recommend separate because the home owner is not likely to know how to maintain the equipment required for a combined exhaust and the last thing the owner will want is flue gases backing up into the house.

 

[Justin tanner]

You should consult some plumbing services for any such type of water heater related problems. They will help you to solve and handle such situations like drain cleaning burlington county nj, drain cleaning camden county nj, etc. within your budget and in less time.