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Forums > Green Building Technologies > Radiant Heating > Subject: Boiler Help Needed

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merimar1User is Offline
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Posts:2
01/16/2006 11:15 PM  
Hi,
I installed a Laars JVT225 two stage boiler that short cycles, fires up for 1 minute then cycles off for 1 1/2 minutes. The boiler is a copper finned tube connected to a 2" manifold with a bypass and a mixing valve and primary pump. I installed 1/2 pex(10,000 feet) in 1 1/2 Maxxon Underlayment. I have 14 zones with one connected to 12' of fin tube. All have individual circulator pumps. I used Wirsbo manifolds and almost all loops have a length of 200' feet. The house is well insulated. Laars looked at the boiler and found no problems with the boiler. I have experimented with differant boiler/supply temps. So far, keeping the boiler temp at 120 and the supply at 100 gives me the longer cycle time as well as the boiler able to cycle between the two stages(depending on the number of zones calling for heat. I used the Wirsbo software to design the tubing layout. The Wirsbo software calculated the output btu at 134,000.
Since the boiler is rated at 189 btu output on the high stage, is it too large and would a smaller boiler eliminate the short cycling? Would a cast iron boiler be a better choice? Should I install a storage tank in connection with either boiler? I have several techs give me conflicting advice so I am somewhat confused.

Any advice would be appreciated.

Thanks,
Mark
UnregisteredUser is Offline
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Posts:2321
01/27/2006 6:36 PM  
No expert here but if only a few zones are "on" your boiler sees a very small load relative to the boiler size. You may have to combine some zones & increase the minimum load. Or downsize if possible the boiler capacity on the lower stage. I can't see a storage tank doing much as it would be insulated and would lose heat slowly. It might help if the circulation goes in & out of it on its trip to the floor with a bypass stream going through your boiler & back to tank. This way the tank water would have cooled down out in the floor before the boiler comes on. Whoever did your design sure screwed up in boiler choice as I see it
merimar1User is Offline
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Posts:2
01/31/2006 9:34 PM  
Thanks for your response.

Since I made the post a few things have changed. The system designer has acknowledge that the Laars 225 is too large and has agreed to a full refund. He suggested looking at a Lochinvar Knight 150BTU condensing boiler. Anyone have any thoughts or suggestions?
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Forums > Green Building Technologies > Radiant Heating > Boiler Help Needed


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