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Hydronic Replacement Boiler Sizing

I am a homeowner. My 10 year old Weil McLain Ultra 230 Series 1 has a leak in the heat exchanger. WM will provide a new heat exchanger at no cost to me for the part plus the cost of labor to change it. I have been unhappy with the reliability of the WM and will be replacing it with a Burnham Alp Boiler.

My questions relates to the size of the new Burnham Alp Boiler. The heating contractor has done a heat loss calculations based on measurements. The heat loss is 197,000 BTUH with an indoor temperature of 75 when it is zero outside. Fuel source is natural gas. Domestic hot water is a zone going into an Amtrol 110 gallon water heater. We are debating between the Burnham ALP 210 and ALP 285. The contractor is leaning toward the 285. My view is that the 210 is undersized and the 285 is a bit oversized. I am trying to understand the ability of unit to modulate itself to the outside temperature and will allow it to run efficiently with reasonable cycling even if the boiler is oversized. Is this a valid way to look at modulation and efficiency? I don't want the boiler cycling and blowing hot air at me and going on and off too frequently. There have been times when the Weil McLain Ultra 230 has not been able to keep up with the heat demand on very cold windy days.

The hydronic system goes into four air handlers two in the unfinished basement and two in the unheated attic.

The home is 4,300 square feet two story with a basement. It has a very significant number of windows to the rear of the home which faces Northeast. The great room facing north has an eighteen foot ceiling.

The home is in southeastern Massachusetts within four miles of the coast (lots of heavy wind). Glass is Pella Proline double pane and insulation is normal for a ten year old custom home. Attic is R-38.

I am thinking of adding radiant heat to the master bathroom.

My wife hates to be cold. Happy wife Happy life.

I would greatly appreciate any insights and knowledge to help me make a decision. Thanks again.


  • JStarJStar Member Posts: 2,668

    If the boiler is feeding hydronic coils in an air system, a modulating boiler is a gigantic waste of money. The coils will need a constant 180F water supply; completely defeating the purpose of a modulating boiler.
    - Joe Starosielec
    [email protected]
  • SWEISWEI Member Posts: 7,356
    What kind of window coverings

    are on those large openings? Do you leave them open at night?  46 BTUs per square foot on a ten-year old house seems high.

    ODR and modulation work just fine on fan coils but you do need to run some calcs to determine the minimum usable supply temp for each coil.  If it comes out lower than about 150ºF, a condensing boiler will not do a whole lot for you.  Lower water temps will result in longer fan cycles and greater comfort -- appropriately sized ductwork and fans help immensely.
  • TonySTonyS Member Posts: 849
    Interesting statement

    Why do you feel the coils would need 180 on anything less than a design day?
  • Boiler

    Yes the boiler is feeding hydronic coils in an air system. I am over my head with this response, but my memory from the time we were building the home was that the town building inspector required a high efficiency boiler which is how I go the Weil McLain Ultra. The WM did not have an outside air temp sensor. The building code issue is why I am looking at condensing boilers most of which come with an outside sensor.

    If I understand your response correctly aside from the building inspector I could simply have had a simple boiler that heats water to 180F.

    What do these facts tell me about what size boiler to choose?

    If I go with the Burnham ALP 285 does that carry disadvantages regarding short cycling or is that less of a factor with coils in an air handler?

    Thanks for your response.
  • JStarJStar Member Posts: 2,668

    Cool/warm air feels uncomfortble, even if it's the appropriate temperature for the heat loss.
    - Joe Starosielec
    [email protected]
  • What kind of window coverings

    We have decorative window coverings on the perimeter of the windows but nothing that would provide thermal insulation. There is a long wooded view behind the home so privacy was less an issue than the view.

    Thanks for the info on ODR and modulation. When you say a condensing boiler will not do a whole lot. Is that in terms of saving money on fuel or providing the heat source to the coils or both?

    Much appreciated
  • TonySTonyS Member Posts: 849
    Proper vent placement

    is the key here. 105 to 110 is fine if the duct is sized properly and the vents are strategically located. 160 degree air can be just as uncomfortable if its blowing on you.

    Well designed and I stress that,Well designed heat pump systems work at low temps and feel as good as any warm air job.
  • JStarJStar Member Posts: 2,668
    edited November 2013

    I suppose that I'm just used to seeing very poorly designed air systems. And we would never install a hydronic coil system from scratch unless it was the absolute only option. We hear nothing but complaints about this type of arrangement. We'll actually be converting a hydronic coil system to radiators for somebody this year.
    - Joe Starosielec
    [email protected]
  • why not

    Why not install cast iron baseboards for 2nd best heating comfort??
  • SWEISWEI Member Posts: 7,356

    only happens when returning water temperatures drop below about 130ºF.  That condition will support a supply temperature of 150ºF, giving an average temp of 140ºF (used for coil sizing purposes.)

    If the coils and ductwork support it, lower water temps will work well.  If they were sized at 180ºF (or higher) and the system is not keeping up on cold days, it may benefit from either hotter water or a change in airflow. 

    It's probable that your system will benefit from a condensing boiler.  It's not guaranteed.  Proper replacement of any HVAC appliance begins with a system analysis and an owner interview.  A contractor who does otherwise should be shown the door.
  • WeezboWeezbo Member Posts: 6,232
    edited November 2013
    are we going vav boxes ...

    outside air ,secondary heating and cooling , wind wrap , external sheet insulation friction fit and vapor barrier details ?

    Because , these are somewhat linked reasons for homes of only ten years of age exhibiting the inability to keep up...


    we have some friends at hvac-talk. com who will provide you with a lot of insight because that too is their road game.

    ask them if 4600 sq ft is something they would go 200 K BTU as a SWAG on a new home.


    sounds like there must be like 30 % outside air lock on the secondary heating and cooling ... ... start a thread there an see what they say ...

    i like to know how their responses take this conversation..
  • ZmanZman Member Posts: 3,478

    The Burham alpine has the exact same exchanger that you WM had.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EastmanEastman Member Posts: 783

    "sounds like there must be like 30 % outside air lock on the secondary heating and cooling"

    I'm not familiar with what you are talking about, what is an outside air lock on the secondary heating and cooling?
  • EastmanEastman Member Posts: 783
    edited November 2013

    Isn't the mod/con needed for the modulation?  There's four air handlers, they're probably zoned.
  • WeezboWeezbo Member Posts: 6,232
    edited November 2013
    well, say you are building healthy

    hate making buildings with sick building syndrome ...

    been at your road game a while ,

    you take all kinds of classes and read more trade journals and been at forced air since they invented it lol..

    a Veritable Melchizedek in the realm of forced air EQ and iaQ not particularly wanting to retool for the job would be adjusting your product to meet the needs of the current environmental health issues ....

    sorry ladd, i am tired this evening ...

    look into the topic , may, be at healthy heating .com and hvac-talk .com there is plenty of back ground info there printed out which you may read . in far less colourful language than my particular style .
  • why not

    I agree the home I had previously with baseboard heat was superior to the hydronic coils I have in the air handlers now.

    At age 70 I don't want to spend up to retrofit the home. If I had it to do over I would defineitely go with baseboard.

  • Alpine

    I believe the Burnham Alpine is a stainless steel heat exchanger and the WM Ultra is aluminum. I had too many problems with the WM to give them my money again. Yes Ultra 3 is supposed to be much better but I am tired of the product.

  • Modulation

    Yes I have four zones (Taco zone controls) of heating and cooling and one zone for the Amtrol

    119 gallon water heater.

This discussion has been closed.


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