How to add radiant heat to steam boiler

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Old 02-06-15, 06:36 PM
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How to add radiant heat to steam boiler

Hi,
I am new to the forum as you can see and I have no HVAC experience.
I am trying to correct the setup of my newly installed kitchen radiant heat. I have a steam boiler with a zone for heat in the basement. The original set up had a circulator, sr501 switch relay, an aquastat that only has one dial set at 160, an auto feed and a manual feed. The upstairs steam system started to have water hammer and the air valves were leaking but this was before the radiant heat was added. Because of the water hammer the contractor decided to run the new radiant heat into the basement baseboard and then use the basement baseboard return into the boiler. That set up did not work for me because I want the basement heat and the 1fl kitchen radiant heat on separate thermostats plus there was no way for me to verify the radiant heat temperature. We consulted with 3 plumbers and have been to 5 plumbing supply stores and no one can agree on how to make this work. I've been told because I have a steam boiler it wonít work, I should use my hot water heater instead, or that it would cost me around $2000 just in parts. I had one plumber come here and he said it was fine with the current setup but I know that isnít correct because the Pex is only rated for 180 degrees and my boiler puts out more than that besides the fact that the return side was lukewarm. My research online leads me to believe the best set up for the radiant heat would be to use a circulator from the boiler to a plate heat exchanger to an expansion tank to a 3 way mixer to zone valve and another circular from the return of the radiant floor tubing. I donít know if having another heating zone affects this set up but any suggestions are truly welcomed. You guys seem to be very knowledgeable about this stuff so I'd really appreciate your help.
 
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Old 02-06-15, 07:41 PM
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Q,
This is just my take on your problem.
First off I would never mix radiant heat with baseboard. You only run about 120į water through the piping for radiant heat. If you run. 120į water through baseboard which is rated for 180į water you won't get enough heat out to heat the space. They must be separate.
You can run a water zone off a steam boiler but both supply & return lines MUST be installed below the water line of the boiler. Since your boiler water heats to 212į for steam you are going to need a mixing valve to lower the temp for the radiant heat. You also obviously need a circulator, a flocheck valve, tstat, operating control, etc.
You shouldn't need an expansion tank because although it is a loop it is not a closed system. The steam boiler is only half full and the heated water expands there. You will put shutoffs on both supply & return with a boiler drain on the return for the initial bleeding. I wouldn't use air vents because once you bleed it no air can get it and if need be it's easy just to bleed.
Just my take,
Good Luck,
 
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Old 02-07-15, 04:36 AM
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Air vents are needed on the steam radiators.

The expansion tank is needed on the radiant floor side of the plate heat exchanger.
 
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Old 02-07-15, 05:30 AM
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Thanks guys,

We were thinking about putting the second circulator at the end of the return system to draw the water through to increase the water flow but I read you should always have the circulator pump away from the boiler not toward the boiler. Iím just trying to avoid some of the problems that people seem to have with the floor not heating up possibly due to water flow issues. Are there any drawbacks to this idea?

Also because I will be using a 3 way mixer do I still need to use an aquastat and would there be any benefit to me using globe valves as opposed to ball valves for this setup?
 
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Old 02-07-15, 08:58 AM
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There's much more to it than meets the eye...

You CAN run a hot water loop above the water line of the boiler.

Take a look at this article:

http://websupport.completewatersyste...a-Steam-Boiler

and this:

https://heatinghelp.com/systems-help...-steam-boiler/
 
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Old 02-07-15, 09:17 AM
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Q,
In my first post I was speaking of air vents on the radiant loop, not rads, and no expansion if coming right off the boiler and not through a plate.
As far as your circulator question you will get better results on the supply side( more pressure ) than the return.
No advantage in globe vs ball valves. Globe valves can leak where ball valve will not.
You still need an aquastat to turn the boiler on to heat the water for the radiant loop if not you're not calling for heat from the steam zone.
I was posting before I read troopers post and I'm afraid I didn't explain the addition of a water loop correctly.
What I was referring to was that the supply and return lines have to be always below the water line.
Trooper is correct and I took it for granted that it was understood that once the water left the boiler it could be pumped anywhere, but trooper explains it much better which is why he is invaluable to this forum.
Sorry for the misunderstanding.
Trooper, thank you for correcting my oversight I did not mean to mislead.
 

Last edited by spott; 02-07-15 at 09:44 AM.
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Old 02-07-15, 09:40 AM
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Perhaps not in your application, but globe valves are FAR superior to ball valves in applications where THROTTLING the flow (i.e. part way open) is required. Just FYI.
 
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Old 02-07-15, 11:17 AM
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I did see a couple of setupís where an indirect tank or the Everhot R.H. 8 heat exchanger tank was used but I really have no space for any of them in the boiler room. Thatís one reason why I figured I would go with using the plate heat exchanger. I checked out those links you posted and Iím not sure if I can use the baseboard radiator as they suggested because the only baseboard heat I have is in the basement and I want them to be controlled by different thermostats.
 
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Old 02-08-15, 07:21 AM
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I was looking over this diagram from one of the links NJTrooper posted and I see where they have a heat exchanger tank. I don't see a 3 way mixer in this layout. My guess is I can use the same layout except I am using a plate heat exchanger instead of the tank version but I thought a 3 way mixer would be a vital part of the set up. Please correct me if I am wrong.
 
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Old 02-08-15, 09:03 AM
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I thought a 3 way mixer would be a vital part of the set up.
Yes, if you are running RADIANT flooring, it would. For BASEBOARD, it's not necessary.

I don't know that I've ever seen it done, but I don't see any reason why you couldn't run two zones, one baseboard, and one radiant, off that heat exchanger. You would treat the heat exchanger as your 'boiler' and set up the piping to the right side of that diagram exactly as you would with a hot water boiler.

Don't neglect the fact that you will need a BRONZE CIRCULATOR between the heat exchanger and the steam boiler.

You would probably need a fairly large heat exchanger though...

I think you may be in 'uncharted waters' with this installation. I can't recall ever seeing this done.
 
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Old 02-08-15, 09:05 AM
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One other thing to be mindful of...

There would exist an 'upper limit' to the amount of heat that you can pull out of the water without having a problem with the boiler being able to make steam.

Did it say anywhere in those articles about a limit on the BTUs?

I don't think I would try to take more than say 10% of the BTU capacity of the boiler out to do hot water heating.
 
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Old 02-08-15, 10:13 AM
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Q: How many hot water zones or indirect heaters can I take off a steam boiler?
A: That depends on the boiler's capacity. You can't take out more BTUs than you put in. I've seen people try to add one too many hot water zones and when it came time to make steam, they were out of luck.

Q: What's a practical limit for a house?
A: Again, a lot depends on the size of the boiler. Usually, you can get away with a 3/4" line, flowing about 4 gpm. That'll deliver 40,000 BTUH, or so to the zone. That's enough to heat a good size zone.

Q: Will I always be able to get 40,000 Btu/hr our of a residential boiler?
A: Yes, if the boiler's net load is over 120,000 Btu/hr.

Q: How come?
A: Because you're playing with the boiler's pick-up factor. The pick-up load usually represents about a third of the net load, depending, of course, on how the installer sized the steam boiler. One-third of 120,000 Btu/hr is 40,000 Btu/hr. That's equal to 4 gpm, about what you can expect to flow through a 3/4" copper line.

- See more at: https://heatinghelp.com/systems-help....2Da2Oyxh.dpuf
Seems to be about 1/3 of the load.
 
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Old 02-08-15, 10:36 AM
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Yes, that's what I read as well, which leads me to believe I should be ok. The radiant heat is for a small kitchen and bathroom.
 
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Old 02-08-15, 10:50 AM
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But you're running two zones... the basement in addition...

How many BTU is the boiler?

How much heat is being put into the basement? (how many feet of fin-tube?)

How big is the kitchen/bath?

Is the radiant 'supplemental'? Or will it be the ONLY heat in those two rooms?

Were there originally steam radiators in those two rooms that have been removed?
 
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Old 02-08-15, 11:12 AM
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Input BTU 150,000, D.O.E Heating Capacity 125,000 BTU. The baseboard in the basement has 15' of fin tube. The kitchen and bath combined for the radiant heat is 170 sf. There are no radiators in those rooms. I considered adding radiators but opted for the radiant heat as to not lose any space.
 
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Old 02-08-15, 01:28 PM
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So you might be taking at most 15K BTUH from the boiler. I don't think that should be a problem.
 
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Old 02-09-15, 01:21 AM
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So you might be taking at most 15K BTUH from the boiler. I don't think that should be a problem.
Thanks for working that out for me.
I was reading about the Taco X-pump block. It seems as though you can eliminate external circulators and mixing valve because its integrated with the heat exchanger. I do however see some setups that include external circulators as well. It's a little pricey but it sounds like it really simplifies things. I'm wondering how well this works. Also what are the drawbacks of having all of the major components in one unit in the event I have to do some troubleshooting on the system. Even though this product has been out since 2010 there's not much posted about it.
 
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Old 02-09-15, 07:08 AM
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Just spoke with the contractor. He said yesterday he saw someone installing radiant flooring and sketched out what they had. It was the same design using the heat exchanger as shown at https://heatinghelp.com/systems-help...a-steam-boiler except they did not have a compression tank. We will be using the plate heat exchanger. I told him we can try it even though the design doesn't have a mixer because that shouldn't be too hard to add but the compression tank is a must. It will properly be about 3 weeks before he comes back but I will definitely let you guys know how it turned out. Thanks for all of your help.
 

Last edited by queensny; 02-09-15 at 08:01 AM. Reason: to specify I will being using the plate heat exchanger not the tank version
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Old 03-27-15, 08:09 PM
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Hello again, You guys were so helpful to me before I'm hoping you can help me again. We started the installation on the boiler side of the radiant heat. The contractor made a tubular heat exchanger. We have 2 circulators. The first circulator is wired to the aquastat and the second circulator is wired to the thermostat. I have a 2 zone taco sr502 switching relay specifically for these 2 circulators. The system seems to work but there are some kinks that need to be worked out. The first circulator stops when the water temperature reaches 100 degrees, which is what the aquastat is set to. The second pump which circulates the water to the supply will shut off once the thermostat reaches the temperature that is set. One problem we are having is a loud noise (hum) from the taco sr502. I have a sr501 that controls the basement heat and there's no hum or buzz. Does anyone have any experience with this? Is this a common issue with the taco sr502? The other problem is figuring out a better method for shutting down the second pump because the room temperature doesn't appear to increase enough to automatically shut down the radiant heat. So in our testing I just manually turn off the thermostat.
 
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Old 03-28-15, 05:39 AM
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Since I have just reviewed this post for the first time I will restrict my remarks.
The contractor made a tubular heat exchanger
Was this designed to transfer enough btu's? Heat exchanger btu transfer is not easy to do. This is a science and engineering feat. But maybe it works.

The level the pipes attach to the boiler should not be at the same level in the boiler, if they are you need to start the boiler when either zone starts. The reason for this if just entering and exiting the bottom of the boiler it will cool down and the boiler will not fire even if it is set up to maintain temp in the boiler. If the boiler is not maintaining temp the aquastat's should not be operating the pumps but starting the boiler and limiting the water temp to avoid steaming. If maintaining temp or not the boiler should fire on a demand. The aquastats can be set at different temps for the two zones.
I have done this successfully with baseboard and radiant above the water level not to exceed 30' of vertical distance above the water line with out heat exchangers.

The noise from the relays in my opinion is not a problem. I have heard it many times from new and old controls but never seemed to affect the operation. It is annoying and you could replace it for that reason. I have had some success trying to locate the noise. Usually it is the relay not pulling in straight.
 
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Old 03-28-15, 09:05 AM
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Rbeck,

Was this designed to transfer enough btu's? Heat exchanger btu transfer is not easy to do. This is a science and engineering feat.
You may be right about the BTU's but I don't know that much about heating systems to say. It's only because of the radiant floor that we are trying to add that I started getting into this. I am trying to learn as much as possible so that I can get it running and have an idea what's wrong if a problem arises in the future.

I don't really know what to expect from the radiant heat. No one that I know has it. When we run the system to test it out I can feel that the floor is somewhat warm where the radiant tubing is as opposed to the small section where we did not lay the tubing.

I have a Honeywell L6006C Aquastat that is wired to the zone 1 leads on the Taco SR502. When the aquastat reaches 100 degrees the circulator from the boiler to the heat exchanger shuts off. The thermostat is wired to the Taco SR502 zone 2 leads. When the set temperature of the thermostat is reached the circulator for the floor supply line shuts down. We actually decided to not wire the radiant heat to turn the boiler on because we haven't seen the boiler water temp drop below 140 degrees. The boiler runs quite often to keep up with the steam heat demand of the 2fl apartment.

The problem I have with the noise that the SR502 is putting out is it sounds more like a compressor than a transformer. It actually makes more noise than the pumps. I thought the first one was defective so I bought another one. At first it was quiet but after everything was connected that one started making a load noise too. I thought maybe it wasn't grounded properly but the ground screws are tight. I would think if it wasn't wired correctly it wouldn't run. We also put foam padding to separate the unit from the wall but that didn't help either. The thing is the SR501 that I have for my basement baseboard heat doesn't have the slightest hum or buzz. Is it the way we wired it or could the thermostat that we are using be contributing to the load hum?
 
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Old 03-28-15, 10:46 AM
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Interested as to how the contractor "made" a tubular heat exchanger....sounds a bit fishy to me. Hope you dont get burned by this "contractor"...and I dont mean by too much heat...bite the bullet and purchase a heat exchanger so that the job is done right..Also make sure the circulator used on the steam side is a bronze or stainless steel bodied pump and protected by a wye strainer....I have done many hot water radiant systems and have had to repair many that were not done right too..don't throw good money after bad.
 
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Old 03-28-15, 01:07 PM
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Interested as to how the contractor "made" a tubular heat exchanger....sounds a bit fishy to me.
I was all ready to buy a heat exchange plate when he asked if we could try to do it with the one he made at the start of the project. I figured if it didn't work then we'll just get the other one.

Turns out it wasn't the Taco SR502 that was causing the noise. A pipe resting against the wall was vibrating with the pump but for some reason you didn't hear it until we mounted the Taco to the wall. Once we took the Taco off the noise went away. Now we have padding behind the Taco and it's only screwed to the wall on one side. That seems to cause the least amount of noise.

I do have one more question. We have the PSI of the expansion tank at 20 PSI. Can't remember where I got this information from but I think it should be more at 15 PSI. How do you determine what the PSI for the expansion tank should be?
 
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Old 03-28-15, 01:54 PM
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How do you determine what the PSI for the expansion tank should be?
It has to be high enough to preclude the possibility of the water changing to steam. Here is a chart to guide you.

Steam Temperature - Pressure Conversion Guide - Technical Reference - Technical Literature - JGB Technical Information Center
 
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Old 03-29-15, 11:45 AM
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Water PSI is 2.31 ft per pound plus 4 PSI but not less than 12 PSI. Normal 12 PSI for a basement application with two floors above is 12 psi.
 
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Old 03-29-15, 02:07 PM
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Thanks guys,
Now all I need to do is figure out how to correct the mistake of not installing a sensor into the floor. I thought any sensor used would take the temperature from the surface of the floor. Worst case scenario I can break a tile in a corner somewhere but I would prefer not to. I read it is best to put the sensor 1/2 way between two runs of tubing but it doesn't say if it is best to have it at the end of the run or if it should be closer to the supply end. Who ever said ignorance is bliss lied. Well at least my experiences will serve to help others that read this post.
 
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Old 03-29-15, 02:31 PM
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Many (most) radiant installations do not use a floor sensor.

Why do you believe that you need one?
 
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Old 03-29-15, 03:03 PM
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The radiant heat is only installed in the kitchen and bathroom to keep the tile warm in the first floor apartment. The heat for the entire house is now controlled by the second floor apartment. This is a complete renovation of the house so I just recently moved the whole house thermostat to the second floor apartment since that is the larger apartment. The first floor apartment now gets too hot which I'll have to work on that as well. While testing the system with a regular thermostat I programmed the thermostat about 6 degrees more than the room temperature but realized the thermostat will never automatically turn the radiant heat off because it will never reach the set temperature. I was trying to avoid leaving it up to someone to have to manually turn the floor heat on and off.
 
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Old 03-29-15, 03:10 PM
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Yeah, if you're only warming the tile and not heating the space with it, then I guess you do need a floor sensor...

You have no access to the underside?
 
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Old 03-29-15, 03:41 PM
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I was looking through my cell phone for some pictures of the tubing to give me an idea of what I can do. I used the precut boards that have the grooves carved out for the pex. So I have 3/4 inch sub floor then the 5/8 inch plywood where the pex sits. I'm a little afraid to try to come in from the bottom in order to get the sensor in between the 2 runs. I already had an incident before the tile was laid. Someone screwed through the pex and we had to break the concrete to fix it. I'm thinking I can open the basement ceiling and put the sensor where the return line is coming from but I'm not sure if I can position it properly. Another option is I can cut away the sheetrock toward the end of the run cause I see there are some grooves that run perpendicular to the pex that I may be able to slip a sensor in. I may have enough space between the wall joists that I'll be able to see the groove.
 
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Old 03-30-15, 09:38 AM
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I think if I read your previous posts correctly that you have a separate pump that feeds the heat exchanger and the underfloor tubing. If that is so then you might get away with using a separate programmable thermostat to control the underfloor heating instead of a floor sensor. I have underfloor tubing in my master bath tile floor and basically I use the thermostat like a time clock to heat the floor when I need it. If the room temperature is less than 70 degrees, water flows through the tubing unless the thermostat is in a setback time period. In my case, if the room temperature is above 70 degrees then I don't need the floor heating. I have it turn on about 2 hours before I go to bed so the floor is warm. Then a setback turns it off for a couple of hours. I turn it back on about 4 AM to allow for a nighttime bathroom break and I leave it on until after I get up in the morning. It is set back again during the day.
 
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Old 04-04-15, 11:08 AM
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I currently have it connected to a programmable thermostat. I haven't had the time to see how long it takes to get the floor to the optimal temperature or how long it takes to cool down. I didn't want to set it by time of day because then the circulator for the system will probably run most of the day. It is for my mother who is retired so it's not like there's a set time that she's out of the house. That's why I figure it's better to program the floor by the temperature rather than the time of day. I didn't get the chance to see what I can do about putting a sensor on the floor but I'll most likely try it where the pex comes out of the floor for the return.
 
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Old 04-04-15, 12:59 PM
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I have done four new homes with under floor aluminum plated in floor heat and never used a sensor in the floor , just zone valves operated by thermostats . The boilers were all controlled by Tekmar out door reset . The number of zones was determined by the number of room that had doors that could be closed , one home has 14 zone valves , the boiler is electric , the owner reports that it is very easy on power and very comfortable.
 
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Old 04-04-15, 04:14 PM
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You said in an earlier post that the underfloor heat is just for comfort and that you are not trying to heat the room(s) with it. In that case you have the option of trying a couple of things.

1. Since you are taking advantage of residual heat in the boiler and not having the underfloor turn it on, you could just run the pumps 24/7 when heat is needed and let the heat be what it is. The cost of electricity for the pumps is small. There will be no additional fuel cost since any heat that the underfloor provides to the overall space will help satisfy the space thermostat when steam is required. The only problem I can see with this option is that the underfloor may get too hot if the water in the boiler goes higher than about 140 degrees for an extended period of time. In that case you could add an aquastat to turn off the pump and limit the temperature.

2. Consider running the underfloor pump(s) whenever the house thermostat is calling for heat. This may be tricky if the steam satisfies the thermostat quickly and the floor may not have time to heat up enough. I have forced hot water heating in my house and I ran underfloor heating for comfort in my kitchen work area. The PEX is installed in aluminum plate between the joists under the subfloor. The total thickness from tubing to top of floor is 1.5 inches of wood. The underfloor is tapped into the normal heating supply and returns. Whenever the house zone calls for heat the water also circulates in the underfloor. Usually by the time the space thermostat is satisfied the floor has warmed up.

3. Consider the possibility of a gravity flow through the underfloor. You would have to remove the pump on the floor side of the heat exchanger to allow full flow. Let the pump from boiler to heat exchanger (system) run with the thermostat (probably not enough time) or install an aquastat to run the system pump and keep the heat exchanger hot. The aquastat could be on the boiler side of the heat exchanger to provide hot water at a set temperature (140 degrees?) or on the floor side at 140* or a lower temperature that provides sufficient heat to the floor. Unless there are a lot of up and down height changes in the PEX, water in the floor loop should flow by gravity through the heat exchanger whenever the temperature of the heat exchanger is higher than that of the return from the PEX tubing. The supply connection should be physically higher than the return. I have similar setup in my vacation house. I have tapped heating PEX into the output pipe at the top of my domestic hot water heater in the basement with the return into a connection at the drain valve near the bottom. The tubing runs on the subfloor under wood flooring in the first floor bathroom. Total thickness of wood above the tubing is about .5 inch. The heating is continuous and comfortably warm all the time. The DWH is set for 120 degrees. No controls, no pumps, and no noticeable increase in propane costs. (I only run the hot water heater when I am there and shut the gas off when I am not there. The space heating for the house is from a wood stove.)

Now that spring has sprung you may not have enough cold weather this season to reach a final conclusion You could try one or another now to get some data or wait until next winter for a longer trial period.
 
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Old 04-04-15, 04:39 PM
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The only problem I can see with this option is that the underfloor may get too hot if the water in the boiler goes higher than about 140 degrees for an extended period of time.
It's a steamer, the water is going to be 212 + at times. I hope he's going to use a mixing valve to drop the temp to 120 or LESS, possibly even as low as 85, since he's only warming the floor.

With 85F water, it could be run all the time and not overheat the floor.

The floor WILL add heat to the room of course.
 
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Old 04-04-15, 04:50 PM
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Down in Post #21 he says that the aquastat controlling the pump from boiler to heat exchanger is set for 100*. That should limit the temp. enough to avoid a mixing valve on the output. I did not take that into account when I made my "140*" comment. Also my other comments about using aquastats for control in the other options could use the existing one(s) he has already installed.
 
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Old 04-04-15, 05:36 PM
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Understood... but what happens when a room thermostat calls for steam? How hot the water gets then? That aquastat is only going to stop the water from getting hot enough to steam when there is no call for steam.
 
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Old 04-04-15, 06:28 PM
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I was referring to the aquastat that controls the pump to the heat exchanger. On a call for steam the boiler will heat up to flash temp and be limited by the boiler aquastat (different than the pump aquastat). At that temperature the pump aquastat is likely to "bounce" a lot off the 100* set point depending on the rate of transfer to the floor loop through the exchanger. Probably would be better to have the pump aquastat sense the output temp to the floor loop and run the boiler side pump only when the output temp drops below 100* or so.

I think the best solution would be a gravity loop with the supply pump controlled by an aquastat on the output of the heat exchanger set to limit the temperature going out to the loop. Of course the success of this arrangement depends on whether the loop can achieve the temperature he wants with a gravity flow.

He won't know if that will work until he tries it. As I mentioned before, I have underfloor in the kitchen on the house zone (pumped). Initially I tried it as gravity but it did not provide enough heat through the 1.5 inches of wood flooring.
 

Last edited by 2john02458; 04-04-15 at 06:43 PM.
  #39  
Old 04-05-15, 10:54 PM
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Hey Guys,

The way the system is currently set up is the aquastat is set to 100 degrees for the floor. I'm not sure if that is too high but since it takes so long to heat up the floor for testing that's what we set it for. I'm not really sure how long it takes for the floor to heat up but I figure a minimum of 2 hours. I have felt the floor get warm so I know it works but since I'm constantly running in and out and working on other projects I'm not sure how long the system is running before I remember to feel the floor. I actually tried to time it today but 3 hours later and it was only warm in the first part of the floor. Now that the weather is warming up it's a little hard to test the system because we disconnected it from the boiler. During the colder temperature we noticed that the demand for steam from the other part of the house kept the boiler temperature around 120-140 degrees, so we only needed to cool the water going to the floor. The pump from the boiler to the heat exchanger turns off with the aquastat so that's no problem. I didn't want the pump that runs the system to stay on all day because I figured it would just run up the electric bill and would defeat the purpose of not installing the electric radiant heat. The other thing that makes me nervous about letting the pump run for 12 or more straight hours is for safety reasons. I don't want to overwork the pump. If it wasn't for those two reasons then I could do like 2john02458 said
you might get away with using a separate programmable thermostat to control the underfloor heating instead of a floor sensor.
Which is how I am currently controlling the system except I manually shut the system down instead of having it programmed by time and temperature.
 
  #40  
Old 04-06-15, 04:42 AM
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The cost to run the pump is WAAAAY less than the cost of electric radiant. Like pennies vs. $1000s. I haven't checked the rated life of a pump like the Taco 007 but I think it can run continuously with no adverse effects. They are used in that mode often in domestic hot water systems. Here is some info I found that suggest that they might last up to 20+ years.

Circulator Pump life | Hearth.com Forums Home
 
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