We just built a building last fall and will be going through the first winter without heat. The PEX is already in the floor for Radiant heat, right now I am researching the best choice for the heat source so we are ready for next winter. My preference would be electric. We have a 200 amp breaker box within 4 feet of where the ½” PEX comes out of the floor. Instead of running one pump and 3 zone solenoid valves like most designs have, I would like to run 3 separate pumps for the 3 zones. I also plan to mount metering valves on all 9 PEX lines going into the floor – hot side and on the cold end of the PEX put thermometer/pressure gauges to “tune” the system and make sure everything is balanced.

I have had suggestions anywhere from standard 40 gallon water heaters to 20kWh Boilers to Reverse Chillers.

I am more worried about the “overall 20 year cost” than the upfront cost. Basically, I just want to get it right the first time.

Thank you in advance for any suggestions or input you may have!


The building specs:
- Located just south of Fort Wayne, Indiana (elevation 791 feet)
- Outdoor temp 0 degrees
– indoor temp 60 degrees
- 28 x 96 with 10 foot walls (24” on center studs and rafters)
- Roof 7/16” OSB, Tar Paper, then Metal Roof
- Exterior Walls 7/16” OSB, House Wrap, Then Vinyl Siding
- 2x6 wall studs with R19 insulation and 5/8” drywall
- Metal siding for ceiling with approximately 12” of cellulose blow in insulation (R36?)
- 3 – 3’x4’ Jeld –Wen double hung windows (2-west side, 1 south side)
- 2 – 10’w x 8’t Garage doors R-18.4 (North side)
- 1 – 8’w x 7’t Garage door R18.4 (west side)
- 1 – 36 x 80” entry door (west side)
- 5” Concrete with rebar 2’oc (“slab on grade” or “monolithic slab”)
- 2” foam under slab
- 1/2" Pex 12” oc (3 zones – 9 loops)



Here are the specs that the contractor gave me on the floor

Heating Load Summary:
- Total System Head = 5.6 ft
- Boiler Load = 46830 BTU/h
- Total System Volume = 27 Gallon
- Total Heated Area = 2688ft2

o Zone 1
Tubing Spacing = 12
Intensity (BTU/H*ft2) = 17.64
Back/Edge Losses (BTU/h) = 2.43
Total Required (BTU/h) = 15802
Total Provided (BTU/h) = 15838

o Zone 2
Tubing Spacing = 12
Intensity (BTU/H*ft2) = 11.56
Back/Edge Losses (BTU/h) = 1.88
Total Required (BTU/h) = 15532
Total Provided (BTU/h) = 15881

o Zone 3
Tubing Spacing = 12
Intensity (BTU/H*ft2) = 22.33
Back/Edge Losses (BTU/h) = 1.78
Total Required (BTU/h) = 10003
Total Provided (BTU/h) = 10041



- Zone 1 28x32 (Garage Area – North side)
o # of Circuits = 3
o Circuit Length = 300’
o Supply fluid temperature = 93.3 degrees Fahrenheit
o Delta T = 20 degrees Fahrenheit
o Gallons per minute = 1.98
o Head = 4.9 feet
o Radiant capacity = 15838 BTU/H
o Required Heat = 15802 BTU/H
o Panel Load = 17978 BTU/H
o Glycol = 45%
o Slab Conductivity = .81 BTU/(h*ft* degrees Fahrenheit)

- Zone 2 28x48 (Machining Area – Middle)
o # of Circuits = 4
o Circuit Length = 300’
o Supply fluid temperature = 85.2 degrees Fahrenheit
o Delta T = 20 degrees Fahrenheit
o Gallons per minute = 1.98
o Head = 5.6 feet
o Radiant capacity = 15881 BTU/H
o Required Heat = 15532 BTU/H
o Panel Load = 18052 BTU/H
o Glycol = 45%
o Slab Conductivity = .81 BTU/(h*ft* degrees Fahrenheit)
 
- Zone 3 28x16 (Storage Area – South side)
o # of Circuits = 2
o Circuit Length = 300’
o Supply fluid temperature = 97.1 degrees Fahrenheit
o Delta T = 20 degrees Fahrenheit
o Gallons per minute = 1.19
o Head = 5.4 feet
o Radiant capacity = 10041 BTU/H
o Required Heat = 10003 BTU/H
o Panel Load = 10799 BTU/H
o Glycol = 45%
o Slab Conductivity = .81 BTU/(h*ft* degrees Fahrenheit)

Why do want to use 3 pumps for such a small HR design?

Your circuit flow rates seem much higher than should be needed. That combined with 300' circuit lengths results in higher requied pump head than should be needed. Why are your circuit lengths exactly 300'...which is rather unusual? What software did you use to get these HR design numbers?

Is electric dirt cheap at your location? If not, an air to water heat pump or ground to water heat pump become the most efficient electric heat source options. Can you use an efficient natural gas boiler?

my thought on the 3 pumps is that i will either be opening or closing solenoid valves or can turn on and off a pump??? i take it that is a bad idea?

all the number came off of a set of papers the contractor we hired gave us when he said the building was done. Things didn't go so well with the contractor, so i am not sure if i can trust these numbers 100%.

The papers about the floor are labeled "RadiantWorks Proffesional" Copyright Watts Radiant 2008

Electricity here is $.13/kwh including all taxes and extras. I would like to eventually add Solar and/or wind to the mix. If i go with Natural Gas, then i am stuck with fossil fuels.

THANK YOU for your input and great questions.

have a merry CHRISTmas!!
jd

Merry Christmas!

I applaud your efforts to avoid fossil fuels. Just keep in mind that your grid electricity may be generated using fossil fuels... Yes, there are very efficient natural gas boilers. You should run the numbers to see what your operational costs would be for the different heat source options. We have free software on our website to do that.

I think you would be better off just using simple zone valves in lieu of multiple pumps. If you don't know what you are doing, you could get some pump flow rate interaction that would be undesirable. Valves are also less expensive and require less electrical power than pumps.

You might want to get a copy of John Siegenthaler's "Modern Hydronic Radiant Heating" to get more educated on this subject.

I would recommend that you first confirm your building heat loss numbers before sizing the required heat source. We have software on our website to do that or you can hire someone to do an ACCA Manual J8 or ASHRAE heat loss analysis.