Advice needed on boiler size for heated floor

[bauer0667]

We got hit with the midwest flooding in March and the Cast Iron Crown 105,000 BTU boiler was submerged under water so I'm looking to get a replacement, however i don't know if i should go with the same size boiler or even replace with a water heater. Thoughts? Below are the details. Any advice is appreciated.

I have an older 41ft x 32ft Red Iron Building with 10ft walls and a 12ft peak in South East Nebraska. The walls are the older 12" insulated panels that lock together. There is R25 Batt insulation in the ceiling with tin under it.

There are two 4ftx8ft Pella windows and a glass walk in door. It also has an insulated 14ftx9ft garage door and a 9ftx7ft insulated garage door.

The concrete is 6" with 2" foam board insulation under it. I have 2 lines that are 300ft long and run the parameter of the garage floor (they are 1 ft in from the edge. I also have 2 lines that are 150ft that run the middle of the garage floor. I now know that wasn't the ideal setup but it's to late.

When my boiler was running last year i had the boiler turned up to 280 degrees with 120 degrees running into the floor with it coming out at 90 degrees. I put in a pipe with a valve on the return to keep the boiler return above 140 degrees. It worked however it seemed to go through a lot of propane and to short cycle.

Thanks for your help.

 

[bauer0667]

I also thought about switching to a hot water heater? Any thoughts?

 

[Randy in Maine]

I have a propane fired Baxi "hangs on the wall" condensing boiler. I am very happy with it. Very efficient.

 

[yeldogt]

I heat my well insulated studio with propane ... two buildings open to each other -- 1700sf. 40k 80% heater.

I'm rebuilding the property and was able to keep it up to temp w/ a 4500 kw electric heater -- that's in the the 13k range.

Its all bout use/ air leaking. Since radiant likes to run -- it pays to make a tight building. It all works together ....

 

[mcbane]

What is the flow rate is into the slab hydronic loops? What are the tubing diameter and length of the hydronic loops? That would tell you how many BTUs are going into the slab and might also suggest whether the system could be improved by increasing the flow rate.

For flow rate, you should try to install a flow meter to get a real number. As a fallback, measure pressure in and out of the loops and check the flow rate curve on the manufacturer's spec sheet to get the likely flow rate.

 

[yeldogt]

I also thought about switching to a hot water heater? Any thoughts?

Go online and try and do a heat loss. Measure this against your propane usage / degree days.

Thinking and knowing are two different things .......

 

[Jackfre]

The tank water heater will be less efficient than your Crown. Those Crown's are good boilers, but with your high water situation I think you pretty much have to go with a wall hung and set it high. Heck of a thing you folks have gone through this year.

 

[86turbodsl]

Your floor delta T sounds a little high, you likely have a slowish flow rate.
If your boiler is short cycling, you probably have much less need than you have boiler.
You REALLY need to do a heat loss/manual j calculation to right size your equipment.
Nobody can just give you an answer without knowing a lot more about your system.

 

[fitter30]

Since your pex loops are two different lengths the 300' should be piped together parallel and the 150' the same with two different pumps. Design water temp for radiate is 5-10* over temperature set point with 10-15* temperature difference between supply and return. Since your building is 1312 sq. ft. with 30 btu's per ft. 40k btu water heater should work. Your cast boiler must of been short cycling alot and that eats fuel. Minimum water temp on a cast boiler is 140* and should have been piped with a bypass and it's own pump to keep its temp up and pex temp down.

 

[yeldogt]

Since your pex loops are two different lengths the 300' should be piped together parallel and the 150' the same with two different pumps. Design water temp for radiate is 5-10* over temperature set point with 10-15* temperature difference between supply and return. Since your building is 1312 sq. ft. with 30 btu's per ft. 40k btu water heater should work. Your cast boiler must of been short cycling alot and that eats fuel. Minimum water temp on a cast boiler is 140* and should have been piped with a bypass and it's own pump to keep its temp up and pex temp down.

This can easily be done with a manifold and one pump ... two if only radiant (for the boiler loop)

 

[bauer0667]

What other information would you need to know? I want to get this right this time. Thank you for your reply.