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variable speed and chimney liner

kevinheat
kevinheat Member Posts: 2
Hi all



I am replacing my furnace and am getting two conflicting pieces of advice.



One contractor sells york and says to not buy variable speed (on any manufacturer) because the boards burn out.



He also says must line the chimney even when buying 95% for the water heater to preserve tuck pointing.



The other one says variable speed is preferable and sells american standard. He recommends two stage instead of modulated because that would allow a zoned system at some point sincehe house is 3300 sq ft and ought to have two furnaces.



This guy says chimney liner may not be necessary depending on the house and recommends waiting to see.



So I am unsure whether to insist on lining chimney and whether to go variable speed or not.



Modulated sounds cool but I kind of believe that a zoning system would do more for comfort than modulated but would be interested in feedback.

Comments

  • kevinheat
    kevinheat Member Posts: 2
    btw

    By the way, I did do some searching for this answer but only found answers from 2009 so not sure what is current advice on variable speed given product updates. Just didn't want you to think that I didn't go to the effort.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Did either one

    of the contractors do a heat loss on your house? If no then insist on one being done. If one of them stated you may need two furnaces then they can be "twinned" and set up as furnace 1 as first stage, furnace 2 as second stage.



    Most new equipment that is going to use a chimney the chimney must be lined.



    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.



    Modulation gives you control over the firing rate depending on outdoor temperature. In other words why fire the unit at full input every-time there is a call for heat when only half the input is needed. You can still zone a warm air system with modulation and get the system control you desire.

    The variable speed (ECM Motor) furnaces are a plus both from efficiency and comfort with warm air. They tend to help eliminate the blowing cold air on start up and on shut down that is typical with warm air systems.



    Definitely have a heat loss done especially if you have added any energy saving concepts to the house such as added insulation or window replacement.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    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.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    If I read the original posting

    correctly I believe there is only one furnace at present in this house, is that correct?



    As for my comment about the chimney the fact that the furnace may be removed from the chimney means the chimney is no longer a factor for heating my suggestion of running a "B" vent up the chimney makes the chimney at that point no longer a chimney but a "Chase". The reason that is necessary is typically the water heater by itself may not be able to power the chimney for proper draft. Then again it may be okay as it probably ran fine by itself in the summer months.



    As for sizing flues on water heaters most who know me here or have attended my classes will tell you my recommendation for modern FVIR water heaters is a minimum 4" double wall flue all the way connector and common vent depending on the chimney height.



    Now furnace fighters two furnace concern is correct if you are going to install two modern furnaces & a water heater into that chimney then it has to have a dedicated liner and even at that it may not be adequate. Then my recommendation would allow two furnaces to be sidewall vented and the "B" vent for the water heater using the chimney as a chase.



    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.



    Two stage systems I have worked on usually means that we have to convert them to single stage in order for the customer to be happy with the heat level and comfort of their dwelling.



    I must say that systems I have seen in the west, south and south west do not tend to have as many problems as most installers in those areas are HVAC folks and they understand air movement.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    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.
  • Bob Harper
    Bob Harper Member Posts: 914
    chimney relining

    A chimney must be suitable for the class of service. When you make a change to the type or efficiency, you should have a Level II inspection per NFPA 211, which will determine if relining or repairs are indicated. This will influence the choices of types of equipment.

    I don't know where you get this x2 limit on sizing as both gas codes allow x7. I agree it performs better when properly sized but I'm not aware of any code limiting at x2. As for sizing the liners, you need to consider many variables. First of all, corrugated liners are de-rated 20% off the top plus another 20% for offsets--the first 90 at the base is baked in. Also, check the sizing on your vent connector because 40mbh input units with less than 3 feet of vertical rise require a 4" connector-not 3". If the WH is to be orphanned then yes it should be relined. However, while both B-vent and aluminum are approved and listed for CAT I venting, both are poor choices. The B-vent is only warrantied for a max of 25yrs for the best brands and one is only 1 yr. Same for alum. liners. You cannot inspect all those joints in the B-vent to see how it is holding up and I've seen joints disconnect in chimneys. Aluminum is too fragile. The Ul 1777 listing was softened last yr against my vote to where it only has to withstand a 100lb dead load vertically and no brush test. I've seen a lot of aluminun liners crushed and torn apart just from installation. They are junk. Also, they don't last when 80% furnaces are common vented. The caps blow or are torn off easily allowing animals to plug them with nests and those sticks pierce the liner. B-vent is hard to support properly in a chimney.

    I recommend only stainless steel with a transferrable lifetime warranty, in either 316Ti or AL29-4c alloys installed to the listing.

    There is only one liner listed for positive vent pressure but no CAT III or IV appliances can be common vented so separate vents for each and they should be two piped unless using a co-axial direct vent system. Regardless, install to the listing then test performance with combustion analysis, check for leaks and install low level CO monitors.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    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.
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