Help in finding a boiler
Last Post 18 May 2015 08:19 AM by BadgerBoilerMN. 6 Replies.
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tbrooksUser is Offline
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29 Apr 2015 09:19 PM
Hello again. It may be a longshot, but I am hoping to get some usefull information, rather than another arguement thread. I have my design figured out and calculated and I am now looking for a boiler. My fuel of choice is Propane gas. Natural gas is not available, and electric rates are high around here. I wouldn't mind at all having a wood boiler, but I would need to construct a place to house it and my budget will not allow for that. I'm trying to keep all costs to a minimum, but I will not cheap out now, and make mistakes that will cost me more money and labor in the future. I would like to have a combi unit, but I'm not sure if that is feasible, or if I can find a model that will perform both tasks efficiently. Of course I want a mod/con with outdoor reset. My total flow rate for my heating system will be 6.85gpm with an output of 18751btu/hr. My design temp is 111*F. I have 10 circuits, and the combine temp drop works out to 56*F. I have searched alot for boilers, but there are just so many out there. From what I have found (and the little that I know) I'm not sure that a single boiler can supply my heating system, let alone supply dhw as well. Worst case scenario, maybe I can find 3 reasonably priced boilers to handle all my needs. I'm still hoping to keep my total materials cost under $5000 for my project, but I'm doubtful thats gonna happen. I was hoping somebody might have an idea of a boiler I can use or at least a better way of searching for what I need. I'm tired of reading spec sheet after spec sheet of boilers I can't use.
BadgerBoilerMNUser is Offline
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30 Apr 2015 08:57 AM
18,751 btu/h ?

Boilers should be chosen first for local support. You will need yearly cleaning and combustion analysis for a propane burning ModCon.

Whether a combi-boiler is appropriate depends on the DHW loads, which you haven't mentioned.

How many zones and the loads in each?
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BadgerBoilerMNUser is Offline
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30 Apr 2015 08:57 AM
dupe
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ronmarUser is Offline
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30 Apr 2015 07:30 PM
I am having trouble getting my brain around your numbers. 6.85 GPM = 411 GPH = 3288 pounds per hour of waterflow... 3288# X 56 degrees of drop = 184,128 BTU/hr...

How did you calculate your numbers? 56F of temp drop seems like a lot...
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01 May 2015 08:38 AM
dt = h/(500q)

dt = 18,751/(500 x 6.85) = 5.47 deg F

This is likely a tighter dt than would be needed and it could likely be relaxed toward 15 deg F.

q = h/(500dt)

q = 18,751/(500 x 15) = 2.5 gpm

A lower flow rate would also have the benefit of reducing the required pump capacity and associated electrical footprint.
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laurawhiteUser is Offline
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18 May 2015 01:14 AM
Great job. Well, I am looking for the same measurement like this and I am glad to see that. Thanks for sharing.
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18 May 2015 08:19 AM
The delta T of the system and the boiler, more especially a ModCon are often, but not necessarily the same.

The make of the boiler will dictate minimum and maximum flow and the type of radiant panel along with specific room heat load and application will properly determine the delta T for the distribution side.

Are on slab, sandwich, sub-floor?
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