variable speed and chimney liner

Venting

CHIMNEY IS NOT A MOOT POINT.



If installing new furnaces, and removing them from the existing chimney, but leaving the hot water heater in place, the chimney does need to be re-sized (by way of liner) to handle the smaller load.



A B-vent chimney can be no more than 2 sizes larger then the largest appliance connector use in the vent system.



In your case, a typical water heater has a 3 inch connector at the draft diverter, and therefore the largest chimney it can connect to is 5 inch.



I assume with 2 furnaces and at least one water heater, the main flue is 6 inches or more, and if a brick chimney probably much larger.





The guy that says wait and see about the chimney is incompetent and should be avoided. Do not insist this guy add the liner, the fact that he does not know is an indication of a lazy heating guy, who will cut corners.



I personally have a York modulating furnace in my home, and it works very well, but in retrospect I would have preferred a 2 stage model. I installed this one in my home as a trial run before selling to customers, as the technology was new at the time. When I installed the furnace, the manual was followed to a tee.



The real key to a reliable furnace is a quality installation including a accurate heat loss analysis. Furnace and duct work need to be sized to the load. (duct work can be larger than needed but can't be smaller) No amount of blower over sizing can fix a bad duct system.



The furnace should be sized to the home, and the duct work needs to be sized to the furnace.



A major misconception going around (even among pros) is that a variable speed motor is a cure all. It's not.



As far as what furnace to buy. I am a believer in buying the heating company, not the manufacture.



As far as what style, I would not install anything less then 95% efficient 2 stage in my own home. Also 2 stage equipment should be controlled by a 2 stage thermostat, not timers. Timers won't stage down, like a thermostat will, but only stage up after a certain time (20 minutes).



Find a heating guy you trust and know will stand behind the product they install.

Sorry Tim

If you are going with a Modulating/Condensing furnace the chimney is a mute point, most will vent out the side of the house and get air for combustion from outdoors, unless the water heater you mention can not develop enough temperature difference in the chimney to get it to pull. Then you may just use the chimney as a chase and run a separate "B" vent just for the water heater up the chimney that is a less expensive alternative than a liner.





I guess I stopped reading after I saw Moot point.



I'm in the Midwest, and in the 60's it became forced air country. And I can tell you, duct work can be just as bad. There was a building boom accompanied by a untrained hvac guy and cheap builder boom at the same time.



Prior to1970 hvac was expected to be 20 to 30 percent of the cost of construction, which allowed for boilers, and engineering of some degree. But with the forced air movement came the make the heating guy figure out what size it needs to be, but don't pay for the engineering movement.

But over time the quality of heating service guy improved. Unfortunately we are seeing another move to the under qualified. Due in part to the hvac "training schools" if you can call them that. The motto seems to be: If they can pay, they will pass.



Installing a liner into the brick chimney will turn the chimney into double wall giving similar ratings as B-vent. And I find the pricing reasonable.

http://www.hartandcooley.com/Products/venting/chimney-liners/Flexible-Aluminum-Chimney-Liners.aspx



I also misread where he said Should have been 2 furnaces, thought he meant has 2 furnaces.



I also use 4 inch as a minimum standard for a water heater, b/c 3 inch allows for no elbows.



But the fact remains the diverter has a 3 inch outlet, and that is what must be used in the max chimney size calculation. Which determines whether the dhwh can provide enough heat into the flue to create draft.









I have some concern about two stage on forced warm air systems especially if you are in the northeastern part of the country. From my experience on thousands of installations 95% of them have insufficient return air (usually only one or maybe two returns) and also issues with supply vent sealing and sizing. I when I bought my house before finishing my basement added four returns to my two return system. It made a world of difference as to air movement and heat circulation to all rooms.



The duct work would have been a bigger issue with single stage. Short cycling, cracking heat exchangers etc... Unless what you were dealing with was a modernization problem. Old gravity heat ducting with supplies on the interior walls and returns on the floor near an outer wall. They worked okay with the old 130 to 150 degree discharge belt drive furnaces from the fifties, but the 100 to 110 degrees of the modern stuff just caused too much draft feeling issues.



Sounds like more a problem with sizing, and general duct design. One stage or 2, if the duct work is wrong, the system wont work right.

Thanks Bob as always

you hit the nail right on the head. I agree about the "B" vent but it sometimes with customers as you know is a matter of price. I have seen some very good installations with "B" vent inside of a chimney it all depends on the installer.



A point about chimneys today, every state should mandate a chimney inspection at time of pulling a permit to insure public safety. If I were a contractor bidding a job an inspection by a chimney professional (usually a chimney sweep who is licensed by the state) would be part of what I would encourage the customer to have.