under-engineered?

Hydronx_2

that is the problem, they don't think they will need much heat, they "don't want to heat it they just want to keep it from freezing." A BTU is a BTU.

Hydronx_2

cheap or efficient engineering?

I am fairly new to the radiant heating world having just changed careers and began a business as a wethead heating contractor.
One of the jobs I am quoting is a 40 stall 24000 sq ft RV storage building 80x300. The owners want to heat it only enough to keep it from freezing. My calculations still show about a 350 mbtu heat load. After my first quote of 3/4" pipe on 18" centers with condensing boilers was way more than they wanted to spend, we spread the pipe to 24" OC and went with standard cast iron boilers.
What I am up against is a supplier in town quoting them on a system design of just putting 3/4" pipe around the perimeter of the building 15 feet in spaced 24" OC.

They have shortened the loop lengths to 300 feet and spec'd a big pump to get lots of flow. But they still need about 39 btu/hr per sq ft from the heated portion of the floor. From the studying I've done this seems risky, but they've been doing this much longer than I have.

Let me know what you guys think or if anyone has experience on this perimeter only strategy.

Unknown

doable. 40 BTUs/sq ft is acheivable in naked slabs but you're jacking the water temp up with that on center. If money is an issue, add more tubing.. if you're down to 300 foot loops go back to 1/2" tubing.. and get back to the condensing boiler with lower water temps. They will save their money in fuel costs fairly quickly with a heat load like that.

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Unknown

where is the building? 14BTUs/sqft on average just to avoid freezing sounds like it could be high if you're in a moderate climate or the building is insulated. maybe. any way you slice it though with that much space you're talking a load that could save money if done efficiently.

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Weezbo

i see nothing wrong with perimeter heating...

only thing that i would suggest though is while the buildings space may very well be used for this purpose today,.....maybe the guy may want to sell the place in the future,where upon all of a sudden the idea of having a bit better control over the space might be a selling feature. go back and restate your case:) then maybe you can sell the condesing and zoning,and perimeter loops

Hydronx_2

building is in Montana -20 below once in a while
R9 insulation in building 4 foot perimeter R5 underslab insulation