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Old 03-11-2013, 10:51 AM   #1
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Condensing vs non condensing


I'm building a new home in Northern Vermont, about 2500 sq ft, and need some advice on which type of boiler to use. I will be using Propane with baseboards throughout and a 55 gallon indirect water heater (lots of showers at once). Some plumbers are telling me to not use a condensing boiler with baseboards, others are telling me to use it but they will need to add more baseboards than normal and an outdoor sensor to adjust water temperature.
I would also need to lower water temp running through the baseboards, but won't it just take longer to heat the house, I'm assuming the extra baseboards help offset this?
I'm also concerned about the added expense of extra baseboard and outdoor sensors, plus I'm sure the boiler is more than a non-condensing, any idea of the number of years to recoup the upfront cost?

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Old 03-11-2013, 12:38 PM   #2
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Condensing vs non condensing


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Originally Posted by vtboy51 View Post
I'm building a new home in Northern Vermont, about 2500 sq ft, and need some advice on which type of boiler to use. I will be using Propane with baseboards throughout and a 55 gallon indirect water heater (lots of showers at once). Some plumbers are telling me to not use a condensing boiler with baseboards, others are telling me to use it but they will need to add more baseboards than normal and an outdoor sensor to adjust water temperature.
I would also need to lower water temp running through the baseboards, but won't it just take longer to heat the house, I'm assuming the extra baseboards help offset this?
I'm also concerned about the added expense of extra baseboard and outdoor sensors, plus I'm sure the boiler is more than a non-condensing, any idea of the number of years to recoup the upfront cost?
First of all the most important information needed to make these kinds of decisions is contained in detailed heat load calculations of the home and water usage information/guestimations. You should never make a decision on what type of equipment/system to install solely on payback. To do so will most times give you a system that is adequate only parts of the time and will cost many times the original installation price to "fix" once you're tired of putting up with the shortcomings.

When sizing any type of heating system it's all about the math. And I'm not talking the financial math here. Do not go with any contractor that does not perform detailed heat load calculations on your new home along with the hot water requirements. After they've done the math they can give you options that will show you exactly how well each different system can perform and should be able to give you a good idea on Life Costs.... a much better measure for choosing than payback.

Let's start with the 55 gallon indirect and the "lots of showers at once" comment. The boiler is your heating source for the indirect and it will take X amount of btu's/hour output capacity of the boiler to produce X amount of hot water per hour. If the "lots of showers" are taken over a long span of time a smaller boiler capacity can handle it. If the "lots of showers" are taken one right after the other or at the same time it can take 2,3 or even 4 times the boiler capacity along with the capacity of the indirect. The indirect manufacturer's all list data that detail the amount of recovery time, gallons per hour at X amount of temperature rise, boiler capacity requirements etc etc etc.. Most hydronic systems with an indirect are set up to stop heating the home when there is a need to heat domestic hot water. That function is independent of the type of boiler used usually. IF you use a cast iron boiler with an built-in indirect coil, then things are different.

No mater the type of boiler you use the system should include an outdoor sensor to adjust water temperature. If this control isn't part of the system it will be less efficient that it can be and the comfort level in the home won't be as good as it could be. The cost of the control is not that much compared to the overall cost of the system and in the case of most high efficient boilers it usually is included as part of the boiler's standard controls.

The use of longer baseboards is because they are rated at X amount of output per foot at certain water temperatures and the gallons per minute that the water is flowing through them. If you reduce water temperature to gain efficiency and comfort you need to adjust the amount of radiation to meet the heating needs of the home at ALL outdoor temperatures.

Hopefully the contractors you are dealing with are supplying you with the information to be able to make an educated decision. With any new home, it's long after all the contractors have left before you start to realize if all the decisions made were the best ones. Modifications after the fact are always very expensive and in some cases, impossible without some amount of tearing apart and rebuilding. If all you're getting is generic sales pitches with no hard facts and numbers.... I'd have to suggest you haven't found the right heating contractor yet.

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Old 03-11-2013, 04:57 PM   #3
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Condensing vs non condensing


May not nee anymore baseboard. What temp is your current boilers high limit set to?

Depending on what brand condensing boiler you get, it may be able to be set to 180 or 190. While you won't get condensing at that water temp, you only need that water temp during the coldest days of the year. The rest of the time you will be able to heat with a cooler water temp. And the boiler will be able to condense. yes, an outdoor reset is needed for the boiler to know what water temp to use.

I have Weil Mclain Ultra boilers on copper baseboard systems, no extra baseboard added. They use 30% less gas a year then they use to, comparing same heating degree day winters to one another.

The indirect is your only real hold up, depending on how many showers at one time. And how hot the people like their water.
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