Underperforming system in cold temps
How would you expect an undersized radiant heating system to perform in cold temps with respect to water flow rates through the floors?
Unfortunately I’m still troubleshooting a radiant heating system - and I find myself always doing so when the outdoor temps drop below 20 degrees F, or so.
Bottom line- I don’t get anywhere close to the designed flow rates through the pex tubes in the floors when all zones call for heat.
I suspected partially blocked lines and the small filters at the mixing valves, but I don’t believe that is the issue because when I manually open the Taco valve to allow more return (cold) water into the supply line, I get much more flow through the floors. When the Taco valve is performing automatically - the flow rates drop significantly. I suspect it’s because not enough hot water is getting to the taco valve to mix with the return water - thus there isn’t sufficient volume of water for the pumps to push to the manifolds and into the floors.
Design is attached:
Big picture overview:
Roughly 7500 sf of heated space. Approx 4000sf of house, 3500 sf of two levels of garage. Bosch FS-151 propane boiler heats both domestic hot water and water for the heating system. Switzer Wood gasification boiler to be installed at later date which will serve as primary heating source, with Bosch propane as a backup off a thermostat when demand isn’t met by wood boiler.
Right now every house zone (9 total) calling for heat based on thermostat setting for each zone.
Design temp for house zones is 120 degrees. I’m getting about 95 degree water to the manifolds , and flow rates into the floors are barely indicating any flow. Again, if I manually adjust MV-1 (taco three way mixing valve) to allow for more cold return water to get to pump P-4, flow rates increase significantly through the floors. I just can’t get proper amount of heated water to do the same.
Boiler fires up to 180 degrees to provide hot water to the heat exchanger to keep domestic hot water requirements met (I suspect) - Bosch SU80 77.4 gal hot water tank
Boiler shuts down and then fires up to about 130 degrees for awhile to provide hot water for the heating system (I suspect).
Would I be correct to assume that when the temps drop significantly outside - that the boiler can’t keep up with domestic hot water requirements (I have four girls in the house that like to take too long of showers) plus the hot water requirements in the floors? If not enough hot water is getting to the Taco three way mixing valve, not enough hot water volume is being mixed and is not getting to the pump P-4 so that I can get sufficient water flow through the lines when the house zones are calling for heat?
I almost wish I had a separate boiler / system for the domestic hot water so that the boiler could stay consistently running at 130 degrees to provide sufficient hot water to the heating system at all times. It seems that when the boiler needs to fire up to 180 degrees for the domestic hot water, the copper lines for the in floor heat immediately cool down fairly significantly. They only heat back up when the boiler shuts down and then fires back up again to 130 for the floor heat.
I can’t really get any good info from the designer - he’s got his check and checked out.
I’d really just like to know if I need a bigger boiler to keep up with the demands. Perhaps it just isn’t enough. I suspected too small of a pump in P-4, but again, it seems to be capable of pushing enough flow through all house zone loops when I allow more cold return water to the pump.
The garage floors use water pumped by a different pump - two zones, and it seems to keep up much better, however , I usually have the temps set much lower. I do have the lower garage at 65 degrees and it seems to keep up fine, but that’s where the boiler is as well as the copper lines , and it’s mostly below grade surrounded by heavily insulated concrete walls. The house is a different story, vaulted ceilings and a lot of windows. Even though it’s spray foamed and well insulated , it’s a big area to heat.
Any suggestions on my next steps? Unfortunately I haven’t found any contractors in this area that would even know where to start with this system.
I find the most knowledge here - thank you in advance
Comments
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First question I like to ask: has it ever worked satisfactorily?
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"Would I be correct to assume that when the temps drop significantly outside - that the boiler can’t keep up with domestic hot water requirements (I have four girls in the house that like to take too long of showers) plus the hot water requirements in the floors? If not enough hot water is getting to the Taco three way mixing valve, not enough hot water volume is being mixed and is not getting to the pump P-4 so that I can get sufficient water flow through the lines when the house zones are calling for heat?"
If the boiler couldn't keep up the output temperature would drop, but you wouldn't see any reduction in flow. If anything the thermostatic valves would allow more flow because they'd be open all the way.
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"Right now every house zone (9 total) calling for heat based on thermostat setting for each zone."
How cold is it outside? Look up the 99% heating temperature for your county in the document below and compare:
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The boiler looks properly sized; maybe a little bit small, but I don't think it will be a problem. And the pump, if anything, may be too large.
Strange, though, that you have mixing valves on the piping after the LLH. If the thought is to limit the water temperature if it gets too hot from the wood burning boiler, I would have installed one mixing valve before the LLH. I could be wrong as I don't do design work with these boilers.
Can you manually open MV-1 to get all hot water and then unplug it so that it won't move to see what the flow is? You will need .5 to .75 gpm at each loop.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
typically when the dhw calls , the heat zones are locked off. This allows the dhw to recover quickly, usually before the heat even drop in temperature. It sounds like you have plenty of boiler power? 15-20 minutes yo recover a cold indirect is about right.
How long does it stay in dhw call? Maybe the indirect is scaled and holding the call too long? Draw the tank cold and time the recovery. Some systems drop the dhw call after a period of time, also.
Put a number to your dhw load is it 60 gallons a day, 250?? Then you know how much boiler time should be needed on a dhw call
Another trick, pull the guts out of the mix valve and run the system, see what that does for the radiant flows, it will be an unknown temperature blend, but it will tell you if the valve is too restrictive. If the manifold flows jump up there’s your problem, Vern😗
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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“First question I like to ask: has it ever worked satisfactorily?”
no Sir, I don’t think it really has. When less zones are calling for heat I might get a slight increase in flow in the zones that are calling for heat.
I just turned up the boiler temperature on the floor heating side, and went to check a Manifold. The temp is now 110 degrees at the manifold and I’m getting barely any flow through the floors. The hot water is just sitting there at the manifolds and just barely going into the pex tubes and into the floor. I once again manually opened the taco valve and went back to check the manifolds and I was getting approx .4 - .5 GPM through every line
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“Can you manually open MV-1 to get all hot water and then unplug it so that it won't move to see what the flow is? You will need .5 to .75 gpm at each loop.”
just tried that. Good idea. I was not even getting .2GPM into the lines. Which makes me think there is an issue in the primary side- getting sufficient water volume to the taco valve…1 -
or as hot rod pointed out - a problem with that Taco Valve.
I have dip switch setting as follows. 1 on, 2 off, 3 on, 4 off.
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“How cold is it outside? “
16 degrees … 99% in my county is -2
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right now I have the boiler setting for the floor heating side to fire up to 155 degrees.
the second attached picture shows two of the three manifolds servicing the house. I turned all valves for the individual loops off except for one and noticed an increase in that single loop to .4gpm. When I open them all back up they indicate barely anything at all.I’ll see what happens over night - perhaps tomorrow I’ll take that TACO valve completely off and dissect it like Hot rod recommended - and see how / if that improves the flow at the manifolds.
Frustrating…
The other issue is the boiler is consistently fired up to 155 right now so without flows through the floors the system will keep calling for heat and the boiler will continue burning propane unnecessarily, I think… which is not cheap.
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Are there any high temp radiant heaters? If not, you don't need any of the mixing valves. Set the modcon to 100F to 120F (or whatever you have the mix set to) and run that straight to your floor heat. You can set the mix valves to fully open and leave them that way by taking the actuator off.
Running the modcon at lower temp will get you a 5-10% increase in boiler efficiency.
As for flow, the number of loops per pump look OK, so if you are not getting enough GPM in a loop, you might have air in the system.
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the boiler piping is a bit confusing. There is a pump in the boiler, a pump above the sep for some reason, and another to the left of the fighter jet? That would be 3 pumps in series?
The separator has a filter function in it, you could pull the strainer out of the Y strainer to eliminate that flow restriction.
Someone made a nice RIB really sale 😏
This piping is an option. Although the boiler and indirect pumps will be in series while the indirect calls. That should recover the tank quickly.
Unless you get inside the boiler to tie in the indirect circ
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
”the boiler piping is a bit confusing. There is a pump in the boiler, a pump above the sep for some reason, and another to the left of the fighter jet? That would be 3 pumps in series?”
Yes three pumps prior to the hyd separator. The top left one in the picture is unused now and will be used later when the wood boiler is installed. The pump in the boiler and the one above the separator is used, and the Low loss header in the boiler is utilized as well.
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Interesting system.
First question I would ask — what is the known (I hope) design heat loss of the house? And, related to that, what is the expected output of the radiant floors? That may be an obvious question, but… in your climate zone, unless the house is pretty tight I would expect a radiant floor only system (I do see a couple of radiators, but they are off one of the radiant manifolds so it is unlikely that they are doing much) to be marginal at best…
OK. Now on to the fun.
First, close both valves going to that big storage tank.
Now lock the heating mixing valves to maximum hot, and close the valves on the recycle lines (this is a test… this is only a test! Not going to leave them that way!).
Zone by zone, initiate a call for heat. The associated pump should run and that zone valve should open. Also, the boiler should run and its circulating pump should run.
For each zone, record the temperature of the water leaving the boiler, the temperature of the water returning to the boiler, the temperature of the water reaching the zone pump, the temperature of the water at the feed manifold, and the temperature of the water returning. from the zone. Also note the flow into the manifold. If there is a way to do it, note the flow through the boiler as well.
Restore the mixing valves and recycle valves to normal and report back… please.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
“As for flow, the number of loops per pump look OK, so if you are not getting enough GPM in a loop, you might have air in the system.”
Air in the system was a thought - but I’m able to get flow through the loops by messing with the TACO valve and using return water. The air would have to be trapped in the primary. Or, I have contamination in the primary filling up the little filter in the taco valve. I’ve pulled some stuff out of there in the past. Sometimes it appeared fully clogged. Yesterday there was a little blockage in that strainer but not enough to slow the water flow down that significantly. But perhaps under pressure and when water is flowing it is clogging the filter and then when I turn the boiler off to open up the valve the contaminants have backed away from the filter by then ?
High temp radiant heater and modcon? I just have two European style Runtal wall mounted radiators in the kitchen area. That’s the highest point in the system so I occasionally will open the little valve to check for air. There’s no adjustments on them at all, though.
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What does the Manual "J" report say is the required BTU/h?
Has a blower door test been done to ensure the structure is tight?
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the pump in the boiler is all you need to the sep. wood boiler ties into sep, loads come off right side of sep.
Indirect is a parallel loop to the boiler, doesn’t need to go through the sep. I would check both sides of it. Possibly an air sep on that loop as it doesn’t go through the sep air elimination.
If you have high temperature loads, then the boiler needs to run that temperature. I’d use ODR to limit running high temperature all the time.
You have 14 radiant loops? So 7- 10 gpm required? 1” Pex is borderline for that flow.
If the design is .65- .75 gpm 14 per loop.? You may need a larger run to the manifold supplies.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
"First question I would ask — what is the known (I hope) design heat loss of the house? And, related to that, what is the expected output of the radiant floors?"
That's in the diagram. In the two boxes labeled "Circuit Information." They're hard to find because there's so much in the diagram but they're there. I count 27 loops, each one seems to be about 5k BTU/hr so maybe 135K from all the loops together.
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“What does the Manual "J" report say is the required BTU/h?
Has a blower door test been done to ensure the structure is tight?”
I’m not sure to be honest. hired a designer for this and gave him the specifics on the house while I built and GC’d it, and hoped he would include it in the plans. A blower door test was never done.
I’d be worried if I was getting proper and designed flow rates through the floors and still had a problem. I’m getting nearly no flow through the floors and the house still holds a reasonably warm temp when it’s 15 degrees outside. It’s just not performing like it should. With hot water actually efficiently flowing through the floor I don’t think I’ll have any issues heating this place even in cold temps and a bunch of north facing windows.
Fortunately I have two wood burning stoves and a high velocity AC system with a heat pump that can supplement some heat while I mess around with this radiant system - but I didn’t even use those at all last night and the temperature is still high 60’s in the house this morning. It’s just that my Hispanic wife has the thermostat set at 73 and without water flowing through the floors at a good rate we never see that.
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”Zone by zone, initiate a call for heat. The associated pump should run and that zone valve should open. Also, the boiler should run and its circulating pump should run.
For each zone, record the temperature of the water leaving the boiler, the temperature of the water returning to the boiler, the temperature of the water reaching the zone pump, the temperature of the water at the feed manifold, and the temperature of the water returning. from the zone. Also note the flow into the manifold. If there is a way to do it, note the flow through the boiler as well.”
This will take awhile and I’ll probably get some help and walkie talkies. I also might need a gun to shoot / record temps of the actual pipes as I don’t have that many temp readouts installed.
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"I’m getting nearly no flow through the floors and the house still holds a reasonably warm temp when it’s 15 degrees outside. It’s just not performing like it should."
I'd like to hear more about this. Are the floors the only source of heat, and they're satisfying the thermostat?
Looking at the diagram, most of the rooms are meant to have a floor temperature of around 82F with an indoor temperature of 72F, when it's -2F outside. If it's 16F right now, your heating load is going to be (72-16)/(72- -2)= 76% of design. That would give a floor temperature of around 79F, which is just barely enough to be noticeable. So it may feel like the system isn't doing anything when actually it's working as designed.
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Email the designer and request the documents.
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”That's in the diagram. In the two boxes labeled "Circuit Information." They're hard to find because there's so much in the diagram but they're there. I count 27 loops, each one seems to be about 5k BTU/hr so maybe 135K from all the loops together.”
Yes Sir, 27 loops total. The highest loop being roughly 6200 btu/hr and requiring .6 GPM flow through the loop. I’ve never seen close to .6gpm through a loop.
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“I'd like to hear more about this. Are the floors the only source of heat, and they're satisfying the thermostat?
Looking at the diagram, most of the rooms are meant to have a floor temperature of around 82F with an indoor temperature of 72F, when it's -2F outside. If it's 16F right now, your heating load is going to be (72-16)/(72- -2)= 76% of design. That would give a floor temperature of around 79F, which is just barely enough to be noticeable. So it may feel like the system isn't doing anything when actually it's working as designed.”
Last night the floors were the only source of heat. I told my wife to turn off the heat pump, and we didn’t utilize the wood burning stoves.
That being said, every single zone is calling for heat, still , the boiler is fired to 155 degrees, and very little flow is actually going through the lines. I would anticipate if the system was only performing at 76% of design that it would allow water through the floors until the temperature set on thermostat was satisfied, and then it wouldn’t call for heat anymore.Bottom line - the system is holding a reasonably warm temp in the house , but doing so extremely inefficiently with water only trickling through the loops and the boiler firing up near constantly
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"Bottom line - the system is holding a reasonably warm temp in the house , but doing so extremely inefficiently with water only trickling through the loops and the boiler firing up near constantly."
With a boiler rated at 137,500 BTU/hr, a back-of-the-envelope load calculation of 135,000 BTU/hr and a temperature at 76% of the delta of the design day, I'd expect the boiler to be running 76% of the time or so. Is that "near constantly"?
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“You have 14 radiant loops? So 7- 10 gpm required? 1” Pex is borderline for that flow.”
27 loops total
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With a boiler rated at 137,500 BTU/hr, a back-of-the-envelope load calculation of 135,000 BTU/hr and a temperature at 76% of the delta of the design day, I'd expect the boiler to be running 76% of the time or so. Is that "near constantly"?
Yes sir I’d say that’s accurate…
It shuts down and then fires up to 180 or so for the domestic hot water, and switched back and forth. When I turned up the boiler temp (dial on the boiler) for the floor heating yesterday , it seems like the boiler is now firing up and keeping 150 degrees for a longer period of time than when it was set to a lower temp.
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I’m tempted to take the small filter off the supply side of the TACO valve and see if I get increased flow at the manifolds, but I’m not really sure if that’d be ok or not. I think I need to flush, clean and refill the entire system this summer anyway to feel more confident about the water quality.
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With domestic hot water probably closer to 100%.
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To add to the confusion about the boiler piping, Why would someone use 1-1/4" shared piping and reduce it to 3/4" before you get to a manifold. If the manifold is only pumping 4 GPM or less thru the 8 loops then you don't need 1-1/4". but if you are moving more than 4 GPM then you don't want to reduce to 3/4". Maybe 1" but not 3/4"
I understand that the design calls for 3/4" copper feeding the manifolds, So why use 1-1/4" to get there? Why not use 3/4" all the way back to the common pipe that is specified as 1"? Looks like the engineer did his homework on paper, the installer didn't follow the directions properly in some cases. (That said: What else did he do wrong that is not noticeable at first glance?)
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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”To add to the confusion about the boiler piping, Why would someone use 1-1/4" shared piping and reduce it to 3/4" before you get to a manifold. If the manifold is only pumping 4 GPM or less thru the 8 loops then you don't need 1-1/4". but if you are moving more than 4 GPM then you don't want to reduce to 3/4". Maybe 1" but not 3/4"
That’s a really good question.
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here’s a picture of the filter on the supply side of the taco valve - I just pulled it off
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That may be a source of reduced flow @Sukhoi29SU
Try cleaning that strained off and putting it back together and see if it works any better.
@EdTheHeaterMan is stating the obvious here. LOL🤣
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Personally I would leave all the strainers out, the mix valve, the Y strainer, etc. The hydraulic sep will remove down to a 5 micron particle.
The strainers were good for start up, I would get rid of that obstacle.
\While not ideal, that very short section of 3/4 at the manifold may not be an issue. You get a velocity increase across it like you do an orifice in a balance valve. Put that low on the list of things to change.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
“Try cleaning that strained off and putting it back together and see if it works any better.”
I’ve done that multiple times… last night included. I understand that will obviously reduce the flow , however I don’t see any improvements immediately after cleaning the filter and reinstalling.
My thought was that perhaps if enough of that stuff is in the primary side that under flow it is completely clogging the filter and once I power down the boiler and take the filter off that some of it has backed off.
Right now I have water turned on from the well and the bottom of the hydro separator completely open to allow water to flush the primary - I have the valves turned off at the supply pumps prior to the secondary
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“Personally I would leave all the strainers out, the mix valve, the Y strainer, etc. The hydraulic sep will remove down to a 5 micron particle.”
Yes sir but those particles are definitely getting past the sep if they are getting to the Taco valve filter, right? Are you saying even if those particles travel through the secondary they will eventually get pulled out by the sep?
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Argh. How long had that filter been in place? That much clogging is insane. It would be a very good idea to find out where that is coming from and fix the problem.
If you find that it is coming from the well, you need a whole house filter on that well supply — and you need to figure out how it is getting into the well to begin with.
I'm interested that the system does seem to be heating the house. I'm even more interested in that the reported low flows do not seem to be compatible with being able to move that much power. Something isn't adding up here.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
yes, those strainers are too fine for hydronic systems. A #20 or 40 mesh is a hydronic size. That sludge should not be an ongoing issue
Once you have the piping sorted out I would run a cleaner, use DI water and add a conditioner
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
“Argh. How long had that filter been in place? That much clogging is insane. It would be a very good idea to find out where that is coming from and fix the problem.”
I agree… I haven’t seen it this bad in awhile.
I attached a hose to the y valve post hydraulic separator and shut the valves off to the secondary. I than opened the well water to the system to flush the primary- I had the hose going for probably 20 minutes. I put the hose in a small clear pitcher and looked for any particles coming out. I did notice a bit of black particles, but not a lot. After flushing the primary I opened up all the valves and turned the boiler back on. I let the boiler heat the water in the primary and went to the manifold to monitor temp and flow. As temp increased at manifold, flow deteriorated. When temp got back to 110 degrees at manifold flow was back to near nothing. Turning off all loops at the manifold except for one resulted in approx .4GPM through that single loop even with it full open. Opening all loops results in negligible flow at all. So back to the boiler, shut everything down, and checked the filter again. This is what I got in about twenty minutes timeframe - which is obviously really bad. So this must be the quality of water from the well. During the house project I had a new well pump put in with a constant pressure system set at 70 psi. Right now incoming water to the system goes through the soft water tank first… I didn’t know whether to have it hard water direct from the well or to have soft water…
I think your idea of a whole house filter from the well is a must at this point.
Although I’m still not convinced that’s the entire problem.
If I do what hot rod is suggesting and take the filter off completely I guess I’d find out - but seeing what came in from the well in a short period of time makes me a bit hesitant to do so.
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I'd say a whole house filter just for the heating system is overkill. What is it, 35-40 gallons? You could just buy bottled water and fill it with a pump. Filling it shouldn't be a regular event once you have it running.
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