Hey guys, I have a new garage and this is the first winter using the radiant heat. I have a grundfos 3 speed pump and i am just curious and to what speed it should be at? (Low, Med or High) Also, what the different speeds will do for me? Like if I want to heat the garage up quicker should i put the pump on high or low? Thanks!
Radiant Heat Pump Speed??
- Thread starter Sublime69
- Start date
bimmer1980
Well-known member
This is a good question...... I'm not completely sure of the answer, however, here is my logic on it....
The water needs to spend sufficient time in the tubes in the slab to transfer the heat to the slab. If your return water temperature is coming back X degrees higher than the slab temp, then the water is moving too fast. i.e. slow the pump down.
It will also make a different on if you are warming a cold soaked slab versus maintaining a slab. If your slab is 32 degrees or colder and you are trying to warm it to 65 degrees, the water will pretty much dump all of it's heat by the time it gets back to the manifold.... Probably use a faster speed.
Once the slab is warmed up, you can probably slow the pump down as your BTU requirement is lower to just maintain. Long term, you would probably see some small energy savings by running a little slower.....
Others can chime in with more info..... I've only had my floor heat installed for one winter, so I'm learning too....
The water needs to spend sufficient time in the tubes in the slab to transfer the heat to the slab. If your return water temperature is coming back X degrees higher than the slab temp, then the water is moving too fast. i.e. slow the pump down.
It will also make a different on if you are warming a cold soaked slab versus maintaining a slab. If your slab is 32 degrees or colder and you are trying to warm it to 65 degrees, the water will pretty much dump all of it's heat by the time it gets back to the manifold.... Probably use a faster speed.
Once the slab is warmed up, you can probably slow the pump down as your BTU requirement is lower to just maintain. Long term, you would probably see some small energy savings by running a little slower.....
Others can chime in with more info..... I've only had my floor heat installed for one winter, so I'm learning too....
American Locomotive
Well-known member
How fast the heat is transferred from the water depends entirely on the temperature difference between the water and the slab. Water doesn't need to spend "time" in the tube to transfer heat to the slab.
The faster your water, the higher the average loop temperature will be. This means the faster your slab will be able to extract heat from the water. If your water speed is too low, your slab will extract all available heat from the water before it exits the slab, which would not be ideal.
However too high of a return temperature may cause your boiler to lose efficiency, especially if it's a condensing boiler. They rely on a fairly cold return water to extract that last little bit of heat energy from the fire.
The faster your water, the higher the average loop temperature will be. This means the faster your slab will be able to extract heat from the water. If your water speed is too low, your slab will extract all available heat from the water before it exits the slab, which would not be ideal.
However too high of a return temperature may cause your boiler to lose efficiency, especially if it's a condensing boiler. They rely on a fairly cold return water to extract that last little bit of heat energy from the fire.
American Locomotive
Well-known member
It might be best just to see what works best for you. Make sure you maintain minimum flow for your boiler (if applicable).
fitter30
Well-known member
Pump speed is determined by feet of head and flow rate of the piping and boiler. Radiate floor systems usually run 5*-10* over thermostat set point max 85*. These systems don't heat very quickly because piping runs in a concrete slab and there a alot of mass to warm up before slab gets warm. Need to know how many feet of pex and size. Pump model #
Mancino
Well-known member
Not to jack your thread OP, but @fitter30 mentioned this in a thread I started also and I didn't quite understand...so do you mean if I want a 50* heated space, the floor temp sensor minimum should be set to 55-60*?
bimmer1980
Well-known member
Yes, roughly..... You will end up with an air temperature gradient from the floor upward. It will be warmest at the floor and decrease as you get further from the floor. Last year I think I had the floor at about 60-65 and the ambient temperature in the garage was about 50-55..... roughly.... At that time, it had minimal insulation, so there would be heat loss thru the building envelope.
Get yourself an infrared thermometer...it helps to determine what is happening with the floor heat and the results....
Dkramer
Well-known member
Bimmer1980 has it pretty correct. A delta T in the 10-20 degree range is typical. The colder the floor the faster the pump needs to run to maintain that Delta T, the warmer the floor the slower the pump speed.
Burl
Well-known member
Lots of things to consider in setting up a system. Personally, if its 55 deg. in my garage, my floor will temp at about that, and that is surface temp. As for your system, try experimenting with pump speeds, flow rates, etc., a little at a time.
kabinenroller
Well-known member
Not that I am an expert on their subject but I can tell you how my system is set up.
This is my seventh heating season with this system.
Very well insulated slab and building. (Stick built, 2x6 walls heating about 1,700 sq.ft.)
Wall mounted boiler unit.
1,400 ft of pex
One zone, six loops
Thermostat controls the pump, when the pump runs the flow triggers the boiler
Thermostat is set at 62 degrees (24x7x365)
Flow rate when system is running is 4.8 GPM
Boiler is set at 110 degrees
The system works very well, the temp in the building varies about 3 degrees from the thermostat setting of 62.
I run the boiler on LP from the same tank the supplies my home so exact amount of LP used in the shop is not known. ( no natural gas where I live)
This is my seventh heating season with this system.
Very well insulated slab and building. (Stick built, 2x6 walls heating about 1,700 sq.ft.)
Wall mounted boiler unit.
1,400 ft of pex
One zone, six loops
Thermostat controls the pump, when the pump runs the flow triggers the boiler
Thermostat is set at 62 degrees (24x7x365)
Flow rate when system is running is 4.8 GPM
Boiler is set at 110 degrees
The system works very well, the temp in the building varies about 3 degrees from the thermostat setting of 62.
I run the boiler on LP from the same tank the supplies my home so exact amount of LP used in the shop is not known. ( no natural gas where I live)
Lonnies Performance
Well-known member
I'm guessing that you have flow indicators on each set loop?
If so, your pump speed is only to used provide the energy needed to meet the set point of the loops.
Open the balance valves fully & put the pump at the lowest speed to see if you can meet your desired loop flow requirements. If not, you have to move up to the next higher setting & readjust your balance valves.
This way you waste less energy by running the pump at the lowest setting instead of the pump working against closed balance valves.
You can also up the flow if you desire to increase the flow by bumping the pump up to the next speed anytime you desire additional heat capacity without readjusting the balance valves.
If so, your pump speed is only to used provide the energy needed to meet the set point of the loops.
Open the balance valves fully & put the pump at the lowest speed to see if you can meet your desired loop flow requirements. If not, you have to move up to the next higher setting & readjust your balance valves.
This way you waste less energy by running the pump at the lowest setting instead of the pump working against closed balance valves.
You can also up the flow if you desire to increase the flow by bumping the pump up to the next speed anytime you desire additional heat capacity without readjusting the balance valves.
Last edited:
fitter30
Well-known member
Even if the loop piping are different lengths and they are piped to a supply and return headers to get equal flow they need to be piped in whats called reverse return. First in last out. So supply header first loop first connection, return header last connection. Design flow for a 300' 1/2" pex loop is 1 gpm. Running 100*+ water temp is fine for heating the air temp but it's warm on your feet and uncomfortable working on the floor.
tricountytrail
Well-known member
100% Correct!!!
That1Guy
Well-known member
I've never understood this concept. What about the loops in the center of the manifold? Isn't that why the manifolds have flow controls on them? The whole "reverse return" concept has always just sounded kinda wonky to me. I'm sure there is something to this concept but I don't understand it and I've never had it explained to me. If someone can put the cookies on the lower shelf for me, I'd appreciate it. TIA
Oh, I dunno. I'm really looking forward to working on my vehicles and laying on my radiant floor with these old bones and 100 - 110 doesn't sound too bad - lol
fitter30
Well-known member
Heres a good explanation of reverse return
https://www.pumpsandsystems.com/what-reverse-return-system
https://www.pumpsandsystems.com/what-reverse-return-system