Adding an indirect tank to an aging boiler


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Old 06-15-09, 10:18 AM
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Adding an indirect tank to an aging boiler

Hi all,

I close on my 1st house next week. We're a family of 4 and it's a 1400 sq ft. ranch with 1950's level of insulation (to be upgraded down the line), if that matters. One of the tasks to tackle before we move in August is adding an indirect hot water tank to the existing oil-fired boiler. The boiler is a 20 year old Burnham that supplies the baseboards and hot water. I don't know many more details about it at this time. The hot water temperature currently fluctuates between 100 and 150F. Since the boiler is still in pretty good working order it was recommended by the home inspector that we use an indirect tank to control the temperature swings and save fuel.

I have a few questions... Sometime in 2010 I'd like to add a drainback solar hot water system to take advantage of southern exposure. Is it worth the added cost now of purchasing a dual-coil tank, or is it better to just use the solar-heated tank as the cold water source for the boiler? Are the Burnham Alliance hydrastone-lined tanks worthwhile (specifically the AL50SL)? Local installers seem to really hate the glass-lined tanks in favor of stainless steel ones. The Burnham specifically touts its suitability to New England water supplies, dunno if that's just marketing.

Are there any considerations in buying an indirect tank that will effect replacing the boiler in a few years?
 
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Old 06-15-09, 07:01 PM
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I'm a fan of a dedicated solar tank (and as it happens, that's what I have...). It does preheat during the winter to an indirect and full solar with a simple manual bypass valve whenever the tank top temperature is acceptable for direct use. Highly recommend this approach. Simple, very effective.

The dedicated tank has better internal ability to stratify (hot water goes to the top, which is good -- keeps the coolest water at the bottom where the coil is). The dual coil tanks, in addition to the extra coil, commonly have an internal baffle to support the coil. That reduces the ability to stratify.

For brands, I'd suggest the HTP Superstor as a reliable, well-built indirect. Stainless. SSU-119 for the solar, SSU-30 for the indirect.
 

Last edited by xiphias; 06-15-09 at 07:16 PM.
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Old 06-16-09, 08:14 AM
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Originally Posted by xiphias
I'm a fan of a dedicated solar tank (and as it happens, that's what I have...). It does preheat during the winter to an indirect and full solar with a simple manual bypass valve whenever the tank top temperature is acceptable for direct use. Highly recommend this approach. Simple, very effective.
Ah, I hadn't considered that solution. In this scenario I'd just buy & install a hot water tank appropriate to our boiler, then when the time comes for a solar system add a bigger tank to hold the solar hot water, and use that as a preheat when it's not hot enough for direct use. That makes sense. There's plenty of room in the portion of the basement dedicated to the heating system for two tanks too. I like it!
 
 

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