Looking for heat source advice for radiant floor heat for a garage

JDmachinist

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.

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)
- 7/16” OSB, Tar Paper, then Metal Roof
- 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)

hot_rod

If electricity is your final choice, maybe look into a air to water heat pump. That would provide the best bang for the buck. Upfront cost and future service need to be factored.

Use one of the online energy calculators to be sure electricity is the best option.

In some areas you see dual fuel applications, taking advantage of off peak costs.

Here is a job I visited in Montreal where they have some interesting rate plans to encourage off peak use. A standard electric boiler with a high efficiency LP unit.

Zman

"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"

OK, this mindset makes it easy:

Buck up and put in the gas line. This will save at least 70% long term over electric.

Purchase and install a fire tube Mod/con boiler sized for your heat loss. Pick a brand that is well supported in your area.

Set up outdoor reset to maximize efficiency and comfort.

A delta P ECM circulator with zone valves is the way to go.
They don't make a circ small enough for your individual zones.
Putting a circ on each zone works well when the zones are either too large or have differing resistance characteristics.
Most people use zone circs because they are uncomfortable sizing circs.

Gordy

Break it down on how much it costs to run your size boiler for 1 hour.

1.68 at .12 kw 14 kw boiler
.40 at .80 per therm 50k Ng boiler.

JDmachinist

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

have a merry CHRISTmas!!
jd

hot_rod

You can add solar thermal collectors to any hydronic system, doesn't matter if it is gas or electric boiler.

Gordy

I think @JDmachinist is talking electrical generation with solar/wind. As hot rod says think thermal solar. much more in possibilities. Hydronics opens that door.

Jamie Hall

Thermal solar backup or primary. Possibly an air to water heat pump for those shady blizzardy days (weeks). Or a gas boiler, as @Zman suggested. Thermal solar can be made remarkably efficient, although it only works when the sun is out -- but with some storage one can do rather well. Very roughly speaking, you should be able to "harvest" upwards of 500 watts as heat per square meter of solar panel.

To date, solar electricity isn't quite as efficient, to put it mildly -- you're lucky to get 200 watts per square meter, if that.