Multiple Zones Vs More efficient Boiler


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Old 11-08-07, 09:22 AM
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Multiple Zones Vs More efficient Boiler

I recently had a new boiler installed in my 2 story house built around 1900 with hot water radiators and an old coal boiler converted to oil. I switched to gas, and I was leaning toward a condensing boiler and 2 zones--one up, one down--to allow for a wood stove on the first floor. My plumber convinced me a more standard boiler (peerless DE 82% AFLUE, direct exhaust) would be easier to maintain. He broke the upstairs into 3 zones--small bathroom, master bedroom, and remaining bedrooms. 1 zone downstairs. Hot water zone gets priority.

This seems a bit excessive for an 1800 sq ft house, and now I need to keep track of four thermostats. I'm worried about short cycling with such small zones and a relatively big boiler (5 fins). And the transformer with all the zone valves makes a pretty good hum--am I burning any savings in additional electric usage? I'm also concerned about all the condensate on the side of the house--the exhaust pipe is fairly short.
I know this plumber has an excellent technical reputation, but perhaps he is a bit conservative with his equipment choices. Did I make a big mistake here?
 
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Old 11-08-07, 10:13 AM
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Findoutlater...

What size is the boiler?

What's your total heatloss?

What's the heatloss for each zone?

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Replacing a new boiler's gonna hurt financially, but if it's about energy efficiency, I'd propose the following.

Prestige 110 (unless they come out with a smaller model)
- single zone, one t-stat in a good reference spot
- running direct to a manifold (only uses the boiler's pump)
- all rads are piped home run back to the manifold - maybe use pex-al-pex
- TRVs on all radiators away from the t-stat location
- leave the radiator(s) closest to the t-stat to be controlled by the t-stat

No idea how much better your gas consumption would be, but your total electrical load will be 14 watts at idle, 74 watts in post purge (you could have up to 1½ hours of constant circ if you wanted), and when firing around 100 watts - 25 watts for the blower fan.

All rooms except the t-stat room can then be individually controlled by TRVs which are totally mechanical and will also help prevent solar gain in any rooms with TRV equipped rads because they'll choke the flow.

If you leave enough flow going to the reference rad(s) then if all of the TRV's are closed, you won't need to use a differential pressure valve.
 
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Old 11-08-07, 10:53 AM
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Findoutlater,

Your plumber was right about maintenance. The less efficient models make up for their lower percentage efficiency in terms of repair costs.

My neighbour has one of those Burnham Revolutions that promises 92% efficiency, but he complains that his gas bill is scarcely less than before, even though the system cost so much.

Even worse, try to find a technician who can work on it! The few boiler men who know how charge a premium for their know-how!

Another technician I was chatting with told me about his own high-efficiency boiler troubles: many delicate parts keep breaking on his, and those parts are very expensive, and are never covered in a repair contact.

Until the technology improves and gets less fragile, until the boiler prices come down, and until there are more technicians out there with the skills to do competant repairs, the high-efficiency boilers are a financially unwise choice.

On the other hand, they are "greener." So that might warm one's heart while handing out green to fix the boiler again...!

J
 
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Old 11-08-07, 12:37 PM
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jurched, a Burnham Revolution is not a modulating condensing boiler. It's a conventional boiler built with cold water protection. It's merely designed to keep itself warm before adding heat to the rest of the house. It has a special controller and a variable speed pump.

I'm not sure what all of these fragile delicate parts are that you say your tech friends are referring to. Just like the FOL's Peerless, my m/c boiler has an electronic ignition and the burner air is fan controlled. His fan or ignition could fail, my fan or ignition could fail...

FOL's controls are a bit simpler, but if he had outdoor reset then that would be just the same. My old oil dinosaur boiler had an outdoor reset controller - makes sense on hydronic systems and works even better when you don't have to worry about low return temps.

His cast iron heat exchanger sections are as good as the castings and method of joining the sections. I'm not sure if the quality of castings and construction is better or worse than it was 20 years ago, we'll see. My heat exchanger is stainless steel and one piece, I'm hoping it will last 15 years. It's a self-cleaning design.

In the meantime at this time of the year, my flue temp is about 90° and will peak at about 130° in deep winter. Your's should reach about 350° or higher to prevent condensation every time it fires. Assuming both methods have complete combustion (both have similar gas valve technology), what do you think the difference in efficiency is? Remember, the difference in efficiency is what goes out the chimney. When I was shopping for a new boiler, I estimated the difference to be about 30% - I still do, but it's hard to get real numbers.

I'm not saying you and your sources are wrong, but the sad truth is that there are far more opinions than facts at the moment and that doesn't bode well as we continue to waste precious resources.
 
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Old 11-08-07, 01:11 PM
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My Basic Question, Zones always good?

Thanks for the replies, but I'm still curious 1.- at 118,000btu and 2000 sf with big cast iron radiators throughout, am I oversize? And 2, with smallish house, are 4 zones plus indirect hw going to cause short cycling? Thanks!
 
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Old 11-08-07, 01:17 PM
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You can never have too much radiation... why does that sound wrong?

Most houses are well under 40 BTUs per SF, so even that would be 72 MBH. Why does everyone grossly oversize?

You can go to slantfin.com and get a free copy of the Heatloss Explorer amd do your own heatloss calculation.
 
 

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