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  1. #1
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    May 2011
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    Default Converting boiler to conventional HVAC with duct work

    I'm looking at buying a home that was built in the 1920's in Michigan. It currently has an ancient boiler system which needs to be replaced. The home does not have any duct work. My question is, is it possible to convert to a normal force air furnace with an a/c unit? what do you think it would cost to convert and add duct work to a 2 story 3800 square foot home?
    thanks

  2. #2
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    Default Re: Converting boiler to conventional HVAC with duct work

    Good news: it can be done.
    Contact local hvac contractors for bids. Prices will vary, but go with the contractor with the best reviews and tract record, someone who you feel you can work with.
    With a two story 3,800 sf home you are looking at 2 condenser units.
    Do you have natural gas supply for heating?

  3. #3
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    Default Re: Converting boiler to conventional HVAC with duct work

    It's hard to say what the best way to go is when you don't know the layout of the house. If you go with two condensers it means your going to need two of everything, it may be the way to go considering the size of your home but look into having your home zoned. Good Luck

  4. #4
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    Default Re: Converting boiler to conventional HVAC with duct work

    Sten and dj1 both make excellent recommendations that you should check out----but as a dyed in the wool boiler man for the past 40 years, let me also recommend that you should check out getting a modern boiler with a forced hot water distribution system of baseboard convectors and/or modern stainless steel radiators----if the existing heating system has any cast iron radiators that are not leaking, not rust-covered, & in good shape, by all means save them & consider using them for the new heating system; cast iron rads are EXCELLENT heating convectors and should be saved if at all possible----sub-floor radiant heat would be another hydronic option, albeit a more expensive one.

    Installation of high-temp plastic PEX tubing thru the wall studs & floor joists when installing hot water systems is much easier these days & may have an advantage over the expense of the forced hot air duct work.

    The cooling aspect, if you chose hydronic, would have to be done with ductless minisplit AC units (Sanyo, Hitachi, Mitsubishi, Friedrich, etc.) that would have the condensers outside for both floors.

    There is also a 4" forced hot air flexible duct system as another option that is available by Unico that cools & heats.

    Consult the Yellow Pages under "heating contractors" and be sure to get 4 to 6 recommendations and price quotes before you decide which is best for you.

    Installation of any new heating system is liable to run you $8k to $15k, depending on which one you choose, and the specific components needed; if you feel the existing heating system definitely has to go, strongly consider making this a part of the bargaining in the selling price of the house; if the seller is or is not willing to consider the cost of a new heating/cooling system as bargaining chip, it could make or break the deal.

    What about the rest of the house, is the roof new, or does it need replacement, how about the siding, the plumbing & electrical systems; how about the septic/cesspool system????

    Any house that old can have a lot of problems in the above areas; make sure you hire a house inspector (Yellow Pages: Real Estate Appraiser) to check everything out before you buy.



    http://www.unicosystem.com
    http://www.sanyohvac.com/multisplit.php
    http://www.sanyohvac.com
    Last edited by NashuaTech; 05-25-2011 at 12:46 PM.

  5. #5
    Join Date
    May 2011
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    251

    Default Re: Converting boiler to conventional HVAC with duct work

    The 1920 home we're buying now was converted 6 years ago. The contractor did descent sheetmetal work, but the units were oversized, not enough supplies so it's NOISY!!!

    Get a load calculation. IF in doubt, undersize the A/C.

    Think of it this way.... if you install 5 tons or 6 tons of cooling capacity, do you really want to pay those cooling bills? IF not, then why oversize it. Bigger blower use more energy and require more ductwork and the units cost more too. Properly sized or even slightly undersized systems are more comfortable because they run longer.


    The home we're buying is 3200 sq ft, has 40 windows, but should have only had a 2.5 ton unit upstairs, 3 ton downstairs, 40 or 60k BTU furnace upstairs and 80k BTU furnace downstairs. They installed 3.5 ton units up and down and a 60k BUT furnace upstairs and 80k BTU furnace downstairs. They put the upstairs unit in the attic.

    IF I had done the installation, I would have installed a 5 Ton 2-stage A/C and 120k BTU furnace and set it up with 4 zones.


    Best of luck. The cost for low end equipment will be around $10k... $15-20k for higher end stuff. You're house is too large for 2 zones, you'll need 2 systems.

    Since MI is fairly mild and has few days over 90F, you have to be careful not to oversize the A/C. I'd guess 100k BTU downstairs, 60k BTU upstairs (heat rises, so you don;t need as much heat upstairs), and probably a 3.0 Ton A/C downstairs and 3 Ton upstairs... Again, heat rises.

    Get a 95% furnace and 2 stage for downstairs if you cna afford it, but I'd just get a single stage upstairs and get lower end A/C units.


    Spend the money on good ductwork and a good clean installation. Give up closet space upstairs rather than installing in the attic.

    Install 6" media air filters and humidifiers on both.

  6. #6
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    Jul 2009
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    Northeast
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    Default Re: Converting boiler to conventional HVAC with duct work

    Quote Originally Posted by motoguy128 View Post
    The 1920 home we're buying now was converted 6 years ago. The contractor did descent sheetmetal work, but the units were oversized, not enough supplies so it's NOISY!!!

    Get a load calculation. IF in doubt, undersize the A/C.

    Think of it this way.... if you install 5 tons or 6 tons of cooling capacity, do you really want to pay those cooling bills? IF not, then why oversize it. Bigger blower use more energy and require more ductwork and the units cost more too. Properly sized or even slightly undersized systems are more comfortable because they run longer.


    The home we're buying is 3200 sq ft, has 40 windows, but should have only had a 2.5 ton unit upstairs, 3 ton downstairs, 40 or 60k BTU furnace upstairs and 80k BTU furnace downstairs. They installed 3.5 ton units up and down and a 60k BUT furnace upstairs and 80k BTU furnace downstairs. They put the upstairs unit in the attic.

    IF I had done the installation, I would have installed a 5 Ton 2-stage A/C and 120k BTU furnace and set it up with 4 zones.


    Best of luck. The cost for low end equipment will be around $10k... $15-20k for higher end stuff. You're house is too large for 2 zones, you'll need 2 systems.

    Since MI is fairly mild and has few days over 90F, you have to be careful not to oversize the A/C. I'd guess 100k BTU downstairs, 60k BTU upstairs (heat rises, so you don;t need as much heat upstairs), and probably a 3.0 Ton A/C downstairs and 3 Ton upstairs... Again, heat rises.

    Get a 95% furnace and 2 stage for downstairs if you cna afford it, but I'd just get a single stage upstairs and get lower end A/C units.


    Spend the money on good ductwork and a good clean installation. Give up closet space upstairs rather than installing in the attic.

    Install 6" media air filters and humidifiers on both.



    How you going to fit all that ductwork in a closet??

  7. #7
    Join Date
    Jun 2010
    Posts
    93

    Default Heat Loss/Heat Gain

    The road map is in having a heat loss and heat gain of the home. Without it you cannot make the best decision in where to invest your hard earned money.

    Second factor is the existing duct work would need to be evaluated for size, insulation and air leakage. Once all these items have been determined you can then start putting options together on the table.

    Hydro-Air (Using a boiler as the heat source) is the most cost effective way to go. Some hints to hydro-air. One hundred percent of the time the coil is oversized to the heating load as it must be sized to meet the cooling load. This allows you to utilize low boiler water temps in the heat mode. Generally you are able to use 160 degree water at design to handle the heat loss. Why is this important. For every 3 degrees you can run a hydronic heating system below 180 degree water you save 1 percent of fuel. Twenty degrees is 6.5%.

    I don't know if you application is oil or gas. If oil, look at boilers such as the Burnham MPO, Viessmann Vitorond 100 and other 3-pass type heating boilers. They are 87% efficiency have a much better insulated jacket compared to traditional pin-style boilers. If gas, at a minimum I would look at the Burnham Series 3, ES2 or condensing boilers from Viessmann and Triangle Tube.

    While I agree with Nashua's take on utlizing cast rads and other means of heating the home I don't agree with his estimation on cost. A 2 and 3 Ton Spac-Pak system material to include condensors cost alone reaches that 15K price point. With mini-splits if doing multiple zoning units depending on the lay-out, type of indoor units and seer chosen could run you up to 10K easily and both are all without labor. Labor cost is not something that can be seen from afar. To many variables in each job and we cannot see them from afar. There is no across the board installation cost.

    While labor rates are different throughout the country the material cost isn't. The numbers I provided are sound and based on current mfg pricing.

  8. #8
    Join Date
    May 2011
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    251

    Default Re: Converting boiler to conventional HVAC with duct work

    Quote Originally Posted by Sten View Post
    How you going to fit all that ductwork in a closet??
    The closet is used as a pipe chase.


    But the other solution is to place one unit in an upstairs closet or if needed the attic (not preferred) then run insulated flex in the attic, and downstairs ductwork in the basement.

    Minimum cost will be $12k for lower end equipment.

    Again, use the smallest units possible to minimize ductwork size, which will reduce costs and keep it from being noisy and inefficient.


    IF you're someone that keeps it 75F in summer and 67F in winter, you don't need big units. Probably only a furnace that's only 60-80k downstairs, 40-60k upstairs and a 2.5 Ton downstairs and 2.5 ton upstairs. Yes, believe it or not, that's all you'll probably need. As mentioned before, if its' not running continuously when it's 0F outside or 92F outside.... it's too big. A unit that's running continuously on a hot day can pull out so much humidity that 76-78F is comfortable because it's only 35-40% humidity... especially with ceiling fans.

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