I'm new to this Forum, and could use some much needed help please, What I have is a 32x64 garage with a 4" slab, using a 40ga. electric Hot Water Heater, with 5/8 Pex with an Oxygen Barrier through out the floor for a total of 2000', Also have a 7 zone manifold purchased from Pex supply store, I am not worried about control each zone of the garage it is all open, so zoning control is not needed, I did the math and for a total of 2000' of pex it takes 27.5 gallons to fill the pex, so I figured a 40gal Hot Water heater would be sufficient enough to do what i'm trying to accomplish, The pump i'm using is a Grundfos Type UP 26-96F Flow range: 0 - 34 U.S. GPM, Just a note i'm using only this pump to move the flow, but have had luck started the process the night before getting the water hot then starting the pump, it was it was 32 degrees when I started it and the next morning it was still 32 degrees what needs to be done to correct this problem I tried attaching a few pictures on what I have, but to much data, all suggestion and replies

A 2,000 sf garage is going to have a substantial heating load. Have you calculated what that is? It would relate to your location, the desired indoor temperature, the construction details and whether or not you insulated the slab enough.

It is unlikely that a hot water tank can supply the required BTUs/hour to adequately heat your 2000 SF of likely high-load zones (i.e., not well-insulated or well-sealed). Before one can properly design a HR floor heating system, one has to first accomplish a proper heat loss analysis (i.e., as ICF suggested). You may want to read about these subjects (please see John Siegenthaler PE, "Modern Hydronic Heating") and use the free DIY analysis/design software on our website to sort out what will be needed to heat your zones as you desire:

Borst Heat Loss Analysis Software

Borst Hydronic Radiant Floor Heating Design Software

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A typical 40 gallon electric water has a 4500 W heating element. Even if it has two elements, only one is normally energized at a time. This is assuming you have a typical 30A circuit breaker and #10 AWG wire supplying the water heater. A 4500 W electric heating element can supply approximately 15,000 BTU/hr. If the electric water heater has the higher capacity 5500 W heating element (roughly the maximum allowed on a 30A circuit) that is still only approximately 18,750 BTU/hr. That isn't much capacity to attempt to heat 2000 sq ft plus the mass of concrete in the floor. If the slab is well insulated from the ground below, you may be able to eventually get the slab temperature up to a tolerable comfort level, but it may take days of heating. If the slab is not well insulated from the ground below, you may need to add a couple more electric water heaters.

I will try the software and see what I come up with, and reply back with results

The slab is well insulated with 2" of insulation the sides are wrapped in rubber sealant, and fars as the ceilings they are 12' tall and the walls are not insulated as of yet just trying to get this system up and running for now and finish garage after I have the heat in place with winter coming on, Is one pump that I described in the earlier post efficient enough to push the fluid throughout that many feet of Pex, or do I need to add

Normally, one FIRST designs the HR floor heating system (i.e., number of zones, PEX diameter, PEX spacing, number of circuits per zone, length of circuits, required supply temp, required circuit flow rates, and resulting PEX hydraulic friction head loss that will result in HR floor system providing the required BTUs/hour to the zones so as to align with the heat loss in these zones) BEFORE selecting/purchasing the pump.

One normally wants to select a pump that will provide the total design flow rate and also provide the total design pumping head (i.e., the total pumping head that aligns with the total HR system hydraulic friction head loss that will occur at the total HR system design flow rate) at the Best Efficiency Point (BEP) of the pump which is typically near the center of pump performance curve (i.e., a plot of the pump actual flow rate versus actual pump head that is obtained from the manufacturer of the pump).

You can enter the pump performance curve for your selected pump and exercise our software to see how well or how poorly the pump you selected will work. Anyhow, this is all explained in detail in the associated instructions for our hydraulic radiant floor heating design software.

With 7 zones in parallel, you have enough pump. On the other hand, just to raise the temp of that concrete by 20F, you need more than 24 hours. Let it run for 3 days and see where you are at.

High temperature, low mass radiant heat is a good choice where you don't need heat all the time.

This is a one zone, 7 circuit system... He may likely have plenty of pump, but he doesn't likely have anything close to adequate heat source...

If his water heater is only putting out 18,750 BTUs/hour (450,000 BTUs/day if operated continuously...not something you would ever want to do), his 2000 SF, 32F initial temp slab will reach 57.0F after 24 hours. This assumes an indoor temp of 70F, convective heat transfer coefficient of 1.56, 4" thick slab, thermal mass density of 150 PCF, thermal mass specific heat capacity of 0.18 BTU/Deg F-Lb, thermal mass upward heat flux R-value of R0.4, thermal mass downward heat flux R-value of R10, and thermal mass emissivity of 90%. However, his indoor temp is not likely at 70F...

If the indoor temp is 60F, the slab will also reach 57.0F after 24 hours.

If the indoor temp is 50F, the slab will reach 52.6F after 24 hours.

If the indoor temp is 40F, the slab will reach 43.5F after 24 hours.

If the indoor temp is 32F, the slab will reach 35.9F after 24 hours.

So the message here is that he would have to heat his space using another heat source that would keep up with the heat loss of the space before he could get the slab temp to be a higher temp than the indoor temp of the space...which is required for a HR floor heating system to actually heat a space... And it would be the indoor temp of the space that would largely be actually heating the slab, NOT the water heater...

Ok all I appreciated all the help, let's try this 2000' of Pex on a 4" insulated slab floor insulated, walls all insulated ceiling is not which is 12' using a 7 zone manifold system that I gave in an earlier post, with 5/8 pex tubing with a total of 27.5 gal to fill lines, what would you propose that will work per what I gave you to heat that much floor space, not worried about controlling different zone at a certain temperature it's obvious 1 - 40gal Hot Water heater isn't going to do the job like I thought it would you guys have been awesome trying to help me on this issue, This is my first go around on Radiant flooring heat, but do not know much about it, Just figured if I could put something inline that will shut the water off instead of continuous flow that it would work just have no clue thinking maybe a immersible thermostatically control thermostat just an thought

walls all insulated

Insulated how? With what?

ceiling is not

No insulation in the ceiling? Is it a stand alone garage or is there a (heated) residence over it?
What is the size and R-value of the garage doors?
Where are you located? What are the outdoor temperatures there? Your slab is starting out at 32F?

Again, without accomplishing a proper heat loss analysis, you can’t size the heat source. If you are unable or unwilling to accomplish this heat loss analysis, you should consider hiring someone to do this for you. This should be an extremely simple heat loss analysis and HR floor heating system design to accomplish.

Depending on the actual heat loss (which is a function of the indoor temp, outdoor temp, and insulation/infiltration characteristics of the building construction), you will likely need a heat source that provides something in excess of 40,000 BTUs/hour (i.e., at least 2-3 times what your water heater is providing). The question is how much in excess, a little or a very lot? Any standard HR thermostat should be able to control this system if a proper HR heat source is used.

What spacing did you use for the PEX?

If you assumed a heat load of 20 BTU a square foot based on zero reality but might be about right with a little surplus or bit light depending on your location 2000 sq feet x 20 = 40,000 BTU hour , does your water heater provide something near that (+ or -)
Next 4 loops of 5/8 in a 500' pattern will create about 5' head at 1 gpm, ( about, I am not looking at my books)
Does your pump provide a pump curve that will push about 1 gpm at 5' head?
rough numbers at 10:30 pm, but in the hunt, more or less. napkin version .01
Dan

Not sure about the pump, but it's a Grundfos Type UP 26-96F Flow range: 0 - 34 U.S. GPM that pretty much all I know about it, the head pressure you mention I have no clue about this, or how to figure to find that number. Over the summer I put up this 32x64 garage, and was talked into putting this radiant system in, so I did, and as I mention the pex has a 2" insulation board it's laying on fasten to wire mesh, and ty-wrap in numerous spots, the garage doors are 2" insulated the ceiling height is 12", the walls are 6" thick with a 1" insulation board against the metal, and blow in insulation between walls, and OSB to top off finish surface, the ceiling is open straight down the middle with no insulation as of yet

Sounds about right Dan. If the PEX spacing is 12” for 2000 SF of installed heating area, he has 7 circuits that would each be 286’ long. If we assume 40,000 BTUs/hour total heat loss and 4,000 BTUs/hour of downward heat loss and if we design for a 15F circuit temp drop delta T, the required floor surface temp would be 79F, the required supply temp would be 99F, and the required flow rate for each circuit would be 0.78 GPM (or 5.5 GPM total). This will then result in a total friction head loss of 4.3’. I expended 10 seconds of my time to enter the parameters into the above linked hydronic radiant floor heating design software...you are most welcome!

According to Grundfos, the UP 26-96 F/BF has a maximum pumping head of 30’ (i.e., at zero GPM) and a maximum flow rate of 28 GPM (i.e., at zero head). With a total friction head loss of 4.3’, the pump flow rate would be 23 GPM. At our design flow rate 5.5 GPM, the pumping head would be 26’. So to use this pump, we would also need to use balance valves to effectively increase the total friction head loss from 4.3’ to 26’ in order to operate the system at 5.5 GPM. So clearly not the right pump selection either. A Grundfos Alpha 15-55 F would be a better pump selection (6.23 GPM at 5.9' head and about 1/10 the electrical energy usage)...but again this is all based on heat loss assumptions that may be far from reality...

the ceiling height is 12"

Previously you noted it was 12 feet. Are you talking about the depth of the ceiling joists, or the height of the ceiling off the floor?

What's your location? Your climate is important with respect to the future performance of your slab.

Speaking of climate ICF, I bet you are greatly enjoying the benefits of your passive solar home design this weekend, eh!

Rather than rely strictly on electric resistance heat to heat the entire shop, which could get to be very expensive*, you might retain your single electric water heater for floor warming and then supplement that with a couple of 1.5 ton (18,000 BTU) mini-split heat pumps to do the bulk of the shop heating (and cooling/de-humidification if necessary). This is assuming that you don't have natural gas available for heating (that would be the way to go if it is available). The advantage of using the high efficiency mini-split heat pumps is the lower operating cost of the heat pumps which should operate using 2.5 to 3.0 times less electricity than purely resistive heating elements for the same number of BTUs generated, and faster response time. Installation of two of these units should be fairly simple in an open shop - just install one unit on one end/side of the shop, and the other on the opposite end/side.

*Assuming your total heat load is around 45,000 BTU, this would require operating three (3) 4500 Watt electric water heating elements or a total of 13,500 Watts or 13.5 KW. Assuming continuous operation over a 24 hour period, this would result in 324 KWH of electricity used. At an assumed cost of $0.12 per KWH electricity cost, this would cost ~$39/day or $1166/month to operate. And the water pump at 205 Watts would add another $1/day or $30/month, so you would be looking at around $1200/month heating cost assuming near continuous operation. Even assuming it only operates 50% of the time, you would still be looking at ~$600/month.

Of course average loads are less than 50% of design loads. And pumping doesn't add to the electric bill in cases of electric heat. But even so, I agree with continuous heating (if that is what you need) using a heat pump (when NG isn't available). I doubt that "bare feet comfort" matters in a garage and cooling can be useful.

Do you have a garage door that provides a good air seal? I have yet to see one.

…or he could use hydroelectric power like us for about $0.004 KWH or just simply elect not to heat the garage at all for $0/month, LOL!

Bringing a cold vehicle into a heated garage (i.e., a vehicle having a temp below the dew point temp of the heated garage) is about the best way to cause massive vehicle corrosion/rust damage. Something to be considered as well…