Boiler/ forced air system?

Discussion in 'HVAC' started by 68bucks, May 14, 2019.

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  1. May 14, 2019 #1

    68bucks

    68bucks

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    I was wondering if anyone had come across a home heating system that uses a boiler to make hot water to supply a coil for a forced air system? I need to replace my home furnace before too long and I would also like to add an outdoor boiler. I thought maybe going to a boiler would marry well with an outdoor boiler. Other advantages I see would be boilers are generally smaller and it's easier to move hot water longer distances than air. We have a long house and are planning to add a master bedroom that would make it even longer. We currently have 2 furnaces one serving each end of the structure. I thought if I went to a boiler for the main furnace I could reduce to foot print and more easily get hot water to the addition and maybe just add blowers in 2 areas. Has anyone heard of such a hybrid system? I have been wondering about the efficiency of such a system too.
     
  2. May 14, 2019 #2

    Sparky617

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    They've done it on This Old House. They'll use a single boiler for hot water, in-floor radiant heat and forced air. Being TOH the systems are usually very high efficiency.
     
  3. May 14, 2019 #3

    68bucks

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    I thought about putting tubing under the floors but I'm worried about possible issues with a large area of hardwood. If I ran the system at low temp it would probably be OK but wouldn't work well with the forced air I'm afraid.
     
  4. May 15, 2019 #4

    Sparky617

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    On the TOH system they had different temperatures of water based on where it was going to be used. Lower for in floor, higher for the water heater and air handler. You temper the water with return water to lower the temperature.

    You really need to talk with a plumber/HVAC guy who works with boiler systems. Around here boilers are pretty much unknown. AC is used for more months than heat so forced air dominates the market.
     
  5. May 15, 2019 #5

    68bucks

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    That's an interesting concept. I have worked with a lot of pump and control systems over the years so I can imagine how you could do that. Seems like it could get complex pretty quick which usually means expensive.
     
  6. May 16, 2019 #6

    slownsteady

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    I'm not sure on where the return on investment on that kind of system kicks in. I converted from forced hot air to hot water baseboard a long time ago My boiler supports five zones including the hot water maker. No special tricks.
     
  7. May 16, 2019 #7

    68bucks

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    My main interest in such a system would be mainly in the ease of moving hot water vs hot air and the smaller size of a boiler. I don't want to go to hot water baseboard as I want the central air still. Due to the long layout of our house having two air handlers and 1 boiler seems attractive. Efficiency is good but not the main focus.
     
  8. May 16, 2019 #8

    WyrTwister

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    We are fortunate enough to have gas for heat . Our furnace is a 90% or 92% forced air unit .

    Is a boiler more efficient / cost effective than that ?

    Wyr
    God bless
     
  9. May 17, 2019 #9

    slownsteady

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    That's a good point. What fuels are available in your area?
     
  10. May 17, 2019 #10

    WyrTwister

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    Butane / propane , natural gas , electricity . Tiny amount of wood . No coal , fuel oil .

    Wyr
    God bless
     
  11. May 17, 2019 #11

    pjones

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    How long is this house?
     
  12. May 17, 2019 #12

    mabloodhound

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    Use an air handler(s) to convert your hot water to hot air heat. Same unit can also be used for your AC. Used a lot on TOH.
     
  13. May 17, 2019 #13

    68bucks

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    We use propane for our heat. Generally we would be limited to propane, fuel oil, wood, or coal. I would love to have natural gas but the chances of that getting to my house are slim.
    Our house as it is is over 100' long. Currently there are 2 furnaces, one servicing each end, so to speak. If we do this addition it would add another 55'-60'. The furnace in the main section of the house would be the one that would need to service the addition. It works well now but is 25 years old so in this project I would replace the furnace. That furnace is about 110' from the new bedroom. I figured my best option would be to relocate the furnace to a more central location for that end of the house. The addition would include a laundry room and a utility area. I would like to use the current utility space for something else. So considering the distance and the actual layout of the rooms it would be a lot easier to run pipe to a coil than ducting connecting to the whole system plus I like the integration with an outside boiler. I just haven't seen a system that uses a boiler to supply a forced air system before. Its common with the outdoor boilers but I'm not sure how the efficiency would be. I also have to figure how to handle the AC. I'm not sure if I would end up needing 2 AC ubits or not. At this point there is only one on the main furnace. The second furnace supplies a large laundry room and a couple spare bedrooms. The bedrooms connect to the main house upstairs and do get some heating/ cooling from that. Its quite an odd house.
     
  14. May 17, 2019 #14

    WyrTwister

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    I personally would try to keep it simple . One condenser for each AHU / furnace .

    Wyr
    God bless
     
  15. May 17, 2019 #15

    mabloodhound

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    By using air handlers, you only need one furnace/boiler. Then position your AH's where most convenient.
     
  16. May 17, 2019 #16

    WyrTwister

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    We have wired multiple modular boilers , for instance , for Churches or schools .

    I think each individula boiler may have had the capability to modulate ?

    In addition to stageing more or fewer boilers to acvomadate the heating load .

    Wyr
    God bless
     
  17. May 20, 2019 at 6:24 AM #17

    maxdad118

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    Why not just add another hvac unit? Benefits of having more than one is if one fails in the winter or summer is you can still be comfortable in another part of the house until it’s fixed? It doesn’t become an ‘emergency’.
     
  18. May 20, 2019 at 12:28 PM #18

    68bucks

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    That would give me 3 total units, having 2 already. Another thing I'm not sure of is how far a condenser can be from the evaporator coil on the AC side? While I might be able to use 1 boiler to feed 2 air handlers for heat, can I do that on the AC or will I need separate condensers? Placing the condenser more centrally is easier being outside.
     
  19. May 20, 2019 at 1:23 PM #19

    WyrTwister

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    1 Condenser for 1 AHU .

    A split system can easily be 50' between units ( condenser & AHU ) .

    Wyr
    God bless
     
  20. May 21, 2019 at 3:49 AM #20

    slownsteady

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    I know this is off-topic a bit, but: 150 foot long house?? Were you previously living on an aircraft carrier? Do you land planes on your roof???
    more seriously, I don't know your plan, your circumstances or the layout of your property, but if you can, why not negate this problem with a more traditional layout of the house?
     

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