Radiant Floor Heat Issues

[Daledorm]

I installed all the ½” PEX tubing in the floor when we built out the bus, and I recently finished setting up the radiant floor heating system. It’s incredible! In cold weather (below 10°F), it keeps the floor between 70–90°F and helps the mini-split stay effective.

Here’s how the system works:
1. Reservoir Tank: The loop starts in a small ½-gallon reservoir tank mounted under the bus. This tank collects return fluid through the cap, which drains out via a ⅝” outlet at the bottom.
2. Pump: The fluid is moved by a 4 GPM AC-powered pump. While it’s effective, it’s fairly loud inside the bus (about 69 d. Both the inlet and outlet are ½”.
3. Heater: The next step is an AC car engine heater. Both the pump and heater are plugged into an outlet under the bus, which is controlled by a switch inside, so I can easily turn them on and off. Like the pump, the heater’s inlet/outlet is ½”.
4. Manifold: From the heater, the glycol runs through a manifold with shut-off valves, allowing me to heat the bus by zones (front/mid/back). Fluid temperatures entering the manifold reach around 140°F.
5. Loops: The heated fluid then travels through the loops that warm each zone. Floor temperatures vary between 70°F (between loops) and 90–100°F directly over the loops.

I started running the system a couple of months ago, just before Thanksgiving. At first, it worked great! While the pump was noisy (around 70 dB inside the bus), the heat was worth it.

However, I noticed the pump sound changed, and when I checked, the glycol was low. I added about ½ gallon of glycol, and the pump sounded better. Soon after, I discovered the heater was leaking from a seam. Since then, I’ve had to top off the glycol every 10 days or so.

When temps reached the high 20s, I turned the system off during the day. But during a 10-day cold snap with highs in the teens, I ran it constantly. That’s when the pump sound changed again. This time, the fluid levels were fine, but the pump wasn’t functioning properly. After shutting it off to cool, I tried again, but the pump still seemed dead. Unfortunately, it’s been too cold to remove and inspect it.

Here are my questions:
1. Could the heater be leaking because the system pressure is too high? Is there an affordable alternative to a hydronic heater?
2. If I switch to a 3 GPM DC pump, would it reduce the pressure while still handling all three loops? A 2.1 GPM pump looks more suited for a fish tank—would it even work?

Thanks in advance for any advice!

 

[cadillackid]

no idea what pump you are using.. but many of these pumps in fact most are not self primers so if the system runs low and gets air in it then the pump wont re-prime.. pumps dont like to run dry... runningthem dry will often cause the to fail prematruely..


I use Davies craig pumps and they have a max head pressure listed.. PEX is designed to handle pretty high pressure and your heating system should get nowhere near..



im not understabnd your reservoire and returning fluid thriugh the cap thing...



form years of designing home hydronic heating systems.. the system has an expansion tank.. most expansion tanks have a bladder that you pump up with a few PSI of air.. a single line goes into the expansion tank, the heating loops dont circulate through the tank.. its just there to have a place for fluid to go when the system heats up... that tank is never full but always has some fluid in it until system design pressure is reached.. with a home/ comercial system you have a city water feed that keeps the system full and at a set pressure...


in your case you could have a reservoire (with a pressure release cap) on the suction side of the system.. the reservoire coud be a zero pressure vessel where expansion simply raises the level of the fluid.. it would be located above the floor and have a single line going to it.. a T into the RETURN to the pump, as the system warms up expanded fluid would raise this level.. when it cools the level would lower..



im assuming you fixed the leak? a hydronic system with a known leak will not run right.. it will permeate air in when the system is cold and off.. then you'll have air in the lines which will make wierd sounds in the pump and could cause it to die over time if it completely airlocked and ran the pump dry to long..


first and foremost fix the leak if you havent already then youll need to bleed the air.

 

[Daledorm]

no idea what pump you are using.. but many of these pumps in fact most are not self primers so if the system runs low and gets air in it then the pump wont re-prime.. pumps dont like to run dry... runningthem dry will often cause the to fail prematruely..


I use Davies craig pumps and they have a max head pressure listed.. PEX is designed to handle pretty high pressure and your heating system should get nowhere near..



im not understabnd your reservoire and returning fluid thriugh the cap thing...



form years of designing home hydronic heating systems.. the system has an expansion tank.. most expansion tanks have a bladder that you pump up with a few PSI of air.. a single line goes into the expansion tank, the heating loops dont circulate through the tank.. its just there to have a place for fluid to go when the system heats up... that tank is never full but always has some fluid in it until system design pressure is reached.. with a home/ comercial system you have a city water feed that keeps the system full and at a set pressure...


in your case you could have a reservoire (with a pressure release cap) on the suction side of the system.. the reservoire coud be a zero pressure vessel where expansion simply raises the level of the fluid.. it would be located above the floor and have a single line going to it.. a T into the RETURN to the pump, as the system warms up expanded fluid would raise this level.. when it cools the level would lower..



im assuming you fixed the leak? a hydronic system with a known leak will not run right.. it will permeate air in when the system is cold and off.. then you'll have air in the lines which will make wierd sounds in the pump and could cause it to die over time if it completely airlocked and ran the pump dry to long..


first and foremost fix the leak if you havent already then youll need to bleed the air.

Thanks for answering! I didn’t think I needed to pressurize the system. I’m just pumping hot fluid through the lines. Should I get a Self-priming pump?

I am in the process of replacing the leaking heater. And the reservoir is just a modified one for a vehicle. https://a.co/d/hf81aMO
I drilled a hole in the top for the incoming fluid. But it’s not pressurized. I also don’t have a bladder. Do I really need one? Currently, the tank, pump, and heater are all below the bus, so below the floor. Do I need to move the tank inside? Then the pump would never run dry as the fluid would be coming from the return lines, into the pump, heater, then tank, and out to the manifold. I didn’t think I needed the return line to the pump, but rather the loop is the return line until the entire thing heats up. Takes a bit longer, but it works. I guess the return loop would speed up that process by half.

I’m in the process of replacing the heater (one without seams).

I really appreciate your input!

 

[Daledorm]

More details for CadillacKid

Thanks for answering! I didn’t think I needed to pressurize the system. I’m just pumping hot fluid through the lines. Should I get a Self-priming pump?

And the reservoir is just a modified one for a vehicle. https://a.co/d/hf81aMO
I drilled a hole in the top for the incoming fluid. But it’s not pressurized. I also don’t have a bladder. Do I really need one? Currently, the tank, pump, and heater are all below the bus, so below the floor. Do I need to move the tank inside? Then the pump would never run dry as the fluid would be coming from the return lines, into the pump, heater, then tank, and out to the manifold. I didn’t think I needed the return line to the pump, but rather the loop is the return line until the entire thing heats up. Takes a bit longer, but it works. I guess the return loop would speed up that process by half.

I’m in the process of replacing the heater (one without seams).

I really appreciate your input!

 

[cadillackid]

so this bottle isnt pressurized? im guessing the cap doesnt seal? so its designed to be big enough that the fluid above it in the heater loops can drain back down to it when the system is off?


then the pump comes on and lowers the level in this tank as it floods the system above?.... and assumes none of the zones will airlock?


or does the cap seal on this tank effectively creating a pressurized system?


you dont need a bladder as you have no external pressure force to keep at bay like a home system.. you do want to run a sealed system that has the ability to expand and contract... ideally you dont drain your loops (replacing coolant with air) every time you shut it off..



fixing the leak regardless is paramount.. thats the first step...


if everything is pressurized and theres no room for things to expand then something will break... coolant and water expand when heating and there needs to be someplace for it to go...



if you look at how your engine cooling system is designed, the cap releases pressure if the system heats up enough to reach that pressure.. so if you filled the system in the bus to the tippy top then went and drove its going to push coolant out the overflow even thugh you are nowhere near boiling point... if you put a cap on it that had no pressure release you would start bursting things..



an open reservoire.. one where the cap doesnt seal will end up in slow loss over times as coolant evaporates... if you sealed the cap on that buick reservoire and filled it all the way up then its possible that there isnt enough expansion room...



how many total gallons of coolant are in the system? with glycol I always used a 10% rule.. which meant if you have 10 gallons of glycol in the system you need a gallon of room for expansion.. thats pretty liberal but it was a safety zone rule of thumb I went on. and by expansion room that would be empty space at room temperature.. assuming a max of 180-190.


system pressure is created as the glycol expands... that is pressure against the outside.. using a pressure release cap.. say 15 PSI if your heaters are rated for that.. meant that if you didnt have quite enough air space some air would release... or some glycol would release if overfilled...



I like my systems to stay flooded all the time with no air anywhere except my expansion vessel.. ie a reservoire above the system with a pressure release cap... on the suction side of the pump.. air naturally wants to go to the top of the system
if you leave it open youll have evaporation and an odor of glycol in your bus anytime you used the system.. thus why I say use a pressure-capable reservoire..



just my 2 cents

 

[BlueBoy-SKO]

The system you have, can you drawl it out on paper?

Radiant floor heat is the way to go! I don’t care where you live or what you’re living in it is the best way to heat.
I have two separate systems one of my house and one in the garage.

 

[Rock-N-Ruth]

I installed all the ½” PEX tubing in the floor when we built out the bus, and I recently finished setting up the radiant floor heating system. It’s incredible! In cold weather (below 10°F), it keeps the floor between 70–90°F and helps the mini-split stay effective.

Here’s how the system works:
1. Reservoir Tank: The loop starts in a small ½-gallon reservoir tank mounted under the bus. This tank collects return fluid through the cap, which drains out via a ⅝” outlet at the bottom.
2. Pump: The fluid is moved by a 4 GPM AC-powered pump. While it’s effective, it’s fairly loud inside the bus (about 69 d. Both the inlet and outlet are ½”.
3. Heater: The next step is an AC car engine heater. Both the pump and heater are plugged into an outlet under the bus, which is controlled by a switch inside, so I can easily turn them on and off. Like the pump, the heater’s inlet/outlet is ½”.
4. Manifold: From the heater, the glycol runs through a manifold with shut-off valves, allowing me to heat the bus by zones (front/mid/back). Fluid temperatures entering the manifold reach around 140°F.
5. Loops: The heated fluid then travels through the loops that warm each zone. Floor temperatures vary between 70°F (between loops) and 90–100°F directly over the loops.

I started running the system a couple of months ago, just before Thanksgiving. At first, it worked great! While the pump was noisy (around 70 dB inside the bus), the heat was worth it.

However, I noticed the pump sound changed, and when I checked, the glycol was low. I added about ½ gallon of glycol, and the pump sounded better. Soon after, I discovered the heater was leaking from a seam. Since then, I’ve had to top off the glycol every 10 days or so.

When temps reached the high 20s, I turned the system off during the day. But during a 10-day cold snap with highs in the teens, I ran it constantly. That’s when the pump sound changed again. This time, the fluid levels were fine, but the pump wasn’t functioning properly. After shutting it off to cool, I tried again, but the pump still seemed dead. Unfortunately, it’s been too cold to remove and inspect it.

Here are my questions:
1. Could the heater be leaking because the system pressure is too high? Is there an affordable alternative to a hydronic heater?
2. If I switch to a 3 GPM DC pump, would it reduce the pressure while still handling all three loops? A 2.1 GPM pump looks more suited for a fish tank—would it even work?

Thanks in advance for any advice!

Since you don't give any details about the pump you have chosen for your floor heat, I am wondering is it a pump that is specifically intended for circulating hot water? A lot of pups will fail if the media you are putting through it is too hot. Another issue could be if you are using a pressure pump instead of a circulation pump this can also lead to pump failure.

 

[cadillackid]

ive had great luck with Davies craig "coolant booster" pumps.. they are quiet, have lower current pull than others and are designed for coolant applications.. they are magnetically driven so. theres no mechanical seal to fail.