Temp stays higher than thermostat -- radiant hydronic heat

PaulG

I just bought a house with in-floor hydronic radiant heat, gas boiler. It's my first experience with this type of system.



There are 5 thermostats (Honeywell T8400B1018) throughout the house. 3 are in bedrooms we don't normally use. I set those thermostats to 55 degrees and close the bedroom doors. In one bedroom, the temperature drops to 55 -- good.



But the temperature in the other 2 rooms stays around 65-70 degrees, and the floor is obviously warm. So it seems like heat is still circulating. I tried swapping thermostats between the 55 degree room and one of the 70 degree rooms, but no change. I tried turning off the thermostats in the 70 degree rooms, but no change. So I don't think the thermostats are the problem.



Any thoughts on what would cause this behavior?



Thanks for your time!

Tim_Hodgson

Over-heating zones

The most likely problem is the when a zone calls for heat, the over-heated zones get some parallel water flow from the other pump. If this is the problem then you can have flow control check valves installed. I would turn off the thermostats in the affected areas today and tomorrow I would check the supply and return piping temperatures for the zones that are over-heating.If they have heat flow then you have found the problem.



Good luck,

Tim

CMadatMe

Zoned

How is the radiant zoned? What does the thermostat tell to open or close. If zone valve or actuators on a manifold are you sure they are closing and not stuck open? If zoned with a circulator pump make sure check valve is installed and operating properly as Tim pointed out.

PaulG

Actuator

Tim, Chris,



Thanks a lot for your replies! Forgive me if I don't have the terminology right -- I'm just learning about radiant heat.



Based on your comments, I think I've found a part of the puzzle. It appears to me that there's an actuator on each of my zones. And the odd thing is, there are 7 thermostats in my house but only 6 actuators.



One of the actuators is labeled "bedrooms" which makes me wonder if I have 2 bedrooms, each with a separate thermostat, connected to 1 actuator. So if either thermostat calls for heat, both bedrooms get it -- seems strange, but would that make any sense?



Also, is there any way for an amateur like me to figure out which actuator a thermostat is connected to, and whether an actuator is working?



Thanks again for your help! Paul

CMadatMe

Zone Control

Yes multiple actuator end switches can be pig tailed to open at the same time as well as a thermostats and can be pigtailed to open an actuator. Is there some type of control the actuators and thermostats are wired to?

PaulG

Pictures

Hi Chris,



Thanks again for your help! I don't really know what I'm looking at in my mechanical room, so I'll try some pictures.



First is the "big picture". The 3 actuators on the upper left connect to pipes going upstairs for rooms where everything works fine. The 3 actuators to their right connect to pipes for downstairs, including the troublesome bedrooms.



Those 3 actuators (second picture) have nothing but copper pipe to the manuals valves below them (third picture).



The fourth picture shows something different between the "upstairs" and "downstairs" parts of the system. There's a single actuator on the pipe leading to the 3 downstairs actuators, followed by what seems to be a temperature gauge (which reads 120 degrees), followed by the green circulator, which is followed by the 3 downstairs actuators.



I'm afraid I can't say for sure what the thermostats are wired to. All I see is a wire coming in to the actuator labeled "Bedrooms". And like I said before there are 7 thermostats in the house but only 6 actuators, so I'm just assuming that the 2 bedroom thermostats are "pigtailed" into the 1 actuator labeled "Bedrooms".



Thanks again -- unless it's obvious to you, it's probably time for me to have a heating guy come out and take a look!

CMadatMe

Pigtailed

Sounds like those bedrooms are pigtailed. Would have to trace wiring. Picture show a crude system. You should call a pro in to inspect the system, find the issue and educate you on how your shstem works.

PaulG

Thanks!

I really appreciate your responses, Chris. I agree with your advice -- will be calling a pro to figure out this issue and get educated about our system.

Ironman

Trouble Zones

Are the areas that you're having trouble on slab? If so, you may have a design/install issue: All radiant floors require a reduced or mixed down water temp. I don't see any mixing valves or other means to control water temps in your pics. It could be done at the boiler with a mod/con. But, even if you had that, there's another problem: Framed floors (wood, tile, carpet, etc.) are low mass and usually require warmer water temps than a slab which is high mass. The slab also requires a more complex means of controlling water temps.



Let me explain: Because framed floors are low mass, they can be controlled with a fixed temp thermostatic mixing valve and a zone thermostat. But, because the slab is high mass it has what is known as the "flywheel effect". That means it can take a lot to get it going and a lot to stop it. If the water temp is fixed temp in a slab, the thermostat may close the zone valve, but the slab may be too hot and will continue to emit heat for a good while because of its mass. The way to compensate for this is to have the water temp in the slab controlled by some form of "reset" to match load conditions. Outdoor reset with an electronic mixing valve or variable speed injection are the two most common methods. Either one will lower the water temp in the slab as the outside temp warms up.



Your pics indicate that you only have one water temp for both the high mass and the low mass. This is improper design and will continue to be a problem until corrected. See the attachment for further explanation.



The 7th zone valve is for your indirect water heater.

PaulG

Design issue

Hi Bob,



Thanks for your response. The trouble areas are indeed on a slab. And your clear explanation helps me understand the "flywheel effect" concept.



I'm going to call a local pro to look at this and propose the best solution to the design issue. But just because I'm curious, I've turned all the thermostats on the slab down to 50 degrees, just to see if the temperature in all the rooms does eventually drop. Seems like that would confirm it's indeed a design issue and not bad actuator(s).



Does that make sense?



Also, my primary concern is whether this problem is causing my heating bills to be higher than necessary -- I don't want to be spending extra money heating rooms that I don't regularly use. If I understand your description of the design issue correctly, that may not be the case. If I occasionally turn one of those thermostats up to 68 degrees for a few days when we have guests, then it takes a few days for the room to cool off when I turn the thermostat back to 50, that's not a concern if my boiler isn't running unnecessarily and it's just that the slab takes a long time to lose the heat.



On the other hand, if I have faulty actuator(s) and heat is circulating in those rooms when I don't need it, I assume that would impact my heating bills.



Does my "logic" make sense?



Thanks again for sharing your expert knowledge!



Paul

Ironman

Makes Sense...

But I doubt that your zone valves are faulty. They rarely stick open, almost always closed, unless they're on an "open" loop where mineral deposits will effect them.



And, you may be using more fuel than necessary as well as damaging your floors if the water temps are too high. What temp is going to the floors? What type/model boiler do you have? Can you post a pic of the boiler and its near piping?

PaulG

More pictures

Hi Bob,



Thanks again for your help!



Here are more pictures. First, a few more pieces of data in case they're relevant.



1) While I was taking the pictures, the boiler came on, ran for only a few seconds, then went off. Seemed odd compared to my experience with forced hot air systems. I haven't noticed that before, but the mechanical room is far enough away from the rest of the house that I don't normally hear when the boiler is running.



2) 24 hours ago, I turned all 4 thermostats on the slab level to 50 degrees. At that time, the room temps were 71-74. Now they're 64-69. So they're going down but very slowly. It was about 30 degrees outside overnight.



3) Just by the feel of my hand, the temperature of the pipes associated with the slab zones are much lower than the upstairs zones. Though I suppose that could be because the slab thermostats are all at 50, not because there's any kind of mixing etc happening.



The pictures:



1) Area around the boiler.



2) Circulator near boiler.



3) Detail on circulator.



4) Detail on boiler.



5) Expansion tank near boiler.



6) Circulator etc near slab zones. The temperature gauge on the upper right reads 120.



7) The boxes on the lower right. The white/red wires on the lower box come from outside the utility room. The upper box says Transformer. The upper grey cable leads to the circulator. The brown wire on top leads to the temperature gauge.



8) Pipes around water main / meter.



I'm not smart enough to figure out if the equipment in pictures 6/7 is somehow supposed to be handling the slab "flywheel effect". I do know that we've got an alarm system that has various sensors for low temperature, CO, etc in case that's relevant.



Thanks again!

Paul Pollets

Here's what I see..

The radiant system doesn't have either a 4 way mixing valve or thermostatic mixing valve, nor an outdoor reset control. The pump for the zone valves doesn't have a pressure bypass differential valve, which should be used when zone valves are installed (or change the pump to a Grundfos "Alpha" pump which has a PBD built-in.

The system has no thermometer on either the supply or return. The system doesn't use flow-port radiant manifolds for distribution, which makes balancing difficult, if not impossible.

CMadatMe

Enough Issues

There are enough issues that as I said before a pro needs to come in to inspect the system, recommend a solution and educate you on how the system works. I see enough issues just by the pics to know I would need to get on the job to co e up with a solution. This is not a diy project nor can any of us give you the solution. Many here have given sound opinions. You need to take them to the pro that comes in and use them as a guide to ask the right questions and get the right solution.

PaulG

Thanks!

Hi Paul, Chris,



Thanks so much for your posts. I know that I can't do this myself and will get a pro. But it's very helpful to hear your comments -- having a little knowledge about the issue should help me feel more comfortable talking with the pro and understanding his proposed solution.



Unfortunately there don't seem to be any contractors in my area registered on heatinghelp.com -- if any of you happen to work near Edwards CO, please let me know!



Paul

PaulG

Really dumb question

Hi guys,



I hope this isn't such a dumb question that you pound your head on your desk. But my wife reminded me that we just spent a lot of money to buy this house and move, so it's not the best time for spending more money.



The fundamental issue is that we're heating space that we don't need to heat, and don't want to pay to heat. Eventually we need to get this fixed. But until it's a better time financially, what if I just manually closed the values (see picture) leading to the zones in question.



1) Would it hurt anything? (Obviously we need to make sure enough warm air flows from the rest of the house into those areas to keep pipes from freezing)



2) Would it be a brute force way of making sure we're not unnecessarily running the boiler due to the design problem?



Thanks again,



Paul

Ironman

Location

How close are you to Denver?



Mark Eatherton is there and you won't find any better. His post are all over here and you can contact through this site by clicking on "Contact this User" under his name. If you're out of his area, he may be able to recommend someone.



I would recommend that you at least have someone who knows radiant look at it and make suggestions; it may cost a lot less to fix some things now than putting it off to the future and the damage becomes worse.



If the pipes going in the slab are cool, then your zone valves are probably OK and you don't need to close the ball valves. Just turn the t'stats down.



One other question: in your last pic it appears that there are 3 supply lines but only 2 return lines in the slab; correct?

PaulG

Supply lines

Hi Bob,



Unfortunately it's a 2.5 hour drive from Denver to my house so Mark probably wouldn't want to do that.



Re: the photo, I just did a bad job as photographer -- those 3 supply lines are from 1 zone, and the 2 return lines are from a different zone.



I found a local company with yellow pages ad and web site claiming to be "the region's experts with radiant heat" so I'll be calling them today.



Thanks, Paul