Gravity System Conversion

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Old 10-07-08, 07:22 PM
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Gravity System Conversion

Hi All,

First order of business. I'm looking at redoing the supply and return piping for the radiators in my mom's house. It is an old gravity system with 4" mains. The reason that I have selected to do this is because she is complaining that her gas bill is realy out of control. The house is pretty old but all of the interior work has been redone. New R13 insulation has been replaced on all exterior walls, all windows sealed up, and so forth. So I don't think very large heat loss is the problem. Is the inefficiency in the oversized mains a large part of the problem????
 
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Old 10-07-08, 07:37 PM
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There is no "inefficiency" in the large main piping but there could be an excessive heat loss from these large pipes if they are not properly insulated.

Large pipes contain a large amount of water and the greater the amount of water in the system the slower it will respond to a call for heat. This is not necessarily a bad thing because it will also take longer to cool off so you lose a bit bringing the heat up and save a bit on the way back down. Uninsulated pipes WILL lose a lot of heat IF they are in an area that is normally unconditioned AND subject to outside temperatures or extreme draftiness.

If the uninsulated pipes are in a relatively closed basement, there is no ceiling and/or insulation in the ceiling (floor) of the room above the pipes then the heat lost is not a complete loss as some will help to warm the floor of the living space.

On the other hand, if the basement has a lot of drafts from outside then you are probably better off insulating the pipes AND the ceiling/floor.

There are other issues if you have a modern low-mass (low water content) boiler installed.

Large gas bills could be related to several different things.
 
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Old 10-09-08, 07:57 AM
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Thanks for the reponse,

I would say that the basement space is realitivly unconditioned. So there is likely some heat loss going on. However I do take note to your point about the boiler being a low mass boiler. The boiler is newer and I believe it could be considered low mass. And like I said the piping system has not been updated from the gravity system that was originally in the house. So I guess the real proplem is that there is a low mass boiler operating in a gravity (I assume this is high mass) system. What corrections can I make to improve this? The radiators on the first floor are very large. Could the radiators be the biggest problem?
 
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Old 10-09-08, 08:52 AM
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What make/model boiler, what size (in BTU/hr or mbh), and how big is the house?

There's several things to assess and do before simply ripping out some perfectly good large mains.

Increasing the overall efficiency of the system probably involves no work at all on the mains. Rather, it more likely will involve adding a boiler bypass if none currently exists, potentially adding an outdoor reset control, and insulating the mains if you/she don't mind having the basement cool off a few degrees. Also keep in mind that adding a little heat to the basement is not a bad thing. Among other things, it reduces the temperature difference between the basement and first floor, particularly if there is no insulation in the basement ceiling.

Large radiators are huge plus, not a minus. They allow you to heat the space with lower water temperatures, and as furd notes, provide radiant heat well after the boiler stops firing, due to their large thermal mass.
 
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Old 10-09-08, 11:19 AM
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What is a boiler by pass? How does it work? Where is it installed?

I will get the specs on the boiler when I get home. Is it possible that the temperature on the boiler is set to high??? Also, I don't see how the large mains and large radiators are good for the overall efficiency of the system. It seems like the larger the amount of thermal mass is the system the more inefficient it may be. I understand the arguement of once their is a large amount of hot water in the radiators makes sense. How ever, it seems like their is alot of heat input necessary to get it there??

Regardless, I appreciate the comments and tech help.
 
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Old 10-10-08, 09:53 PM
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A boiler bypass is simply a piping assembly that allows the majority of the system water to "bypass" the boiler so that cold(er) water from the system return does not cool the the internal parts of the boiler to the point that the water vapor in the combustion gases start to condense in the boiler's gas passages. Such condensation is akin to acid rain and will deteriorate the boiler. Using a boiler bypass is quite common and often required on systems that have a large amount of water in the piping but a small amount of water in the boiler.

It may be that the temperature in the house is set higher than necessary but that is up to the occupant. My mother never lived in a house with central heating until I installed a hot water baseboard system. She never got used to setting the thermostat and often would open a window (even in the winter) if she got too hot. As a rule older people like warmer temperatures than do younger people. Even now with me being in my late fifties I cannot stand to be in a house where the temperature is above 70 degrees. I keep my own house at 68 degrees until later at night when I bump it up to 70. I also wear only pants and a tee shirt most of the time.

Or are you asking about the water temperature in the system? The circulating water temperature should be such that it keeps the house at the temperature set by the room thermostat. Depending on several variables that may be as low as 100 degrees or it may require 180 degrees. The best system is one that automatically sets the system water temperature to the proper setting based upon the outside temperature. This is called outdoor reset or ODR and it can both reduce the amount of fuel burned and increase indoors comfort.

Large piping and large radiators have little to do with system efficiency nor does the thermal mass of the entire system. Efficiency is nothing more than the ratio of work (heat) out compared to the work in to the system. You cannot get more heat out of the system than you put in to it. In practical matters you won't even get as much heat out as you put in. Where the thermal mass comes into the equation is that you have a source of heat (the burner/boiler assembly) that outputs the heat at a fixed rate of X BTUs per hour. The boiler/burner assembly is either on or off, maximum output or zero output unless you have a modulating burner which is another discussion. Maximum efficiency is achieved with the burner off (no input=no output=100% efficiency) so it can be stated that if you want a 100% efficient heating system you can have it by merely never allowing it to operate. Of course that is also a ridiculous statement because the only purpose of a heating system is to add heat to your home.

That statement IS, however, an excellent introduction to heating system efficiency because the biggest loss in a heating system (for various reasons) is the constant on/off cycling of the burner. The longer a burner is operating the more it can be operating at its maximum efficiency. By using a system with high thermal mass the burner will have a longer on cycle AND a longer off cycle and THAT is what will give a greater SYSTEM efficiency as long as the heat losses of the system are properly controlled to be ONLY to heat the areas that one desires to heat to the set temperature.

Ideally the heat input to a house should be regulated to exactly match the heat lost. A large thermal mass, properly controlled, will accomplish this with minimal problems.
 
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Old 10-22-08, 09:26 PM
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Furd and Rbeck,

Thanks to both of you for the responses. Sorry it took so long to respond. I've been busy with my own house, and this has sort of dropped to the bottom of my priority list. However it is back on the radar. It sounds like there is alot more involved than I think, but nothing that I can't get a handle on. I guess I should give a better description of the system and prehaps you guys could help out.

The house is an old 3 story colonial in south Jersey. The first and second floor is on one zone, and the third floor is on another. Right now I'd like to focus on just the one zone. Lets call this zone one. The first floor has free standing cast iron radiators. Their are six CI radiators in all on the first floor all of which are realitivley the same size. The actual volume I'm not sure of. But they have 1" screw pipe inlets and outlets. The second floor has four four smaller free standing CI radiators, all of which are similar in size. The second floor radiators all have 3/4" screw pipe inlets and outlets. The boiler is set up in the concrete block basement. Servicing both the first floor and second floor are a 3" cast iron main, and a 3" cast iron return. Again, just a reminder that the first floor and second floor are on the same zone (same circulator pump). The supply and return run pretty much the whole length of the basement. I'd say about 30' long a peice. The boiler was replaced about 5 years ago. So the boiler is newer. Make and model I'm not sure of. But will get. Immediatley exiting the boiler, and immediatley returning to the boiler is 1" copper. The 1" transistions abruptly to the 3" main. Same thing for the return. The question I had orginally asked came about because I thought that it was a resonable theory that their is a large amount of heat loss going on in the basement. As I stated above, the basement is an uninsulated concrete block wall basement. So the basement acts like a big heat sink. Currently the 3' main and return are not insulated. Is the problem that I'm pumping alot of heat out through the basement???

Regardless, what I really want to do is seperate the first and second floor into two seperate zones. As Furd stated in his post the easiest way to say money is to not run the heater. So if the first and second floor is zoned, you will not waste money heating space that is not occupied. The main culprit is heating the entire house at night. Everyone sleeps on the second floor of the house so heating the down stairs at night is a waste... I guess what I really am asking is this. Since I want to zone the first and second floor anyway, what is the best way to repipe the radiators? I planned on running a main and a return for each zone. With a pump on each zone. What is the best way to do this??

Any help is greatly appreciated.
 
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Old 10-22-08, 10:31 PM
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In my first response (post #2) I stated that insulating the pipes and the basement ceiling would be money well spent with a good short-term payback.

As for re-piping the first and second floors to allow for two independent zones...how hard it would be depends entirely on how the second floor radiators are plumbed to the main supply and return piping. If there is a second main supply and return for the second floor then it will be relatively easy. On the other hand, if the second floor radiators are piped to the first floor radiators it will be rather difficult. If the first and second floor radiators all have independent piping running to the basement where they connect to the existing 3 inch mains it may not be all that difficult.

If you can post several pictures of the piping (ideally with labels identifying the various pipes) it might help. I'm thinking that merely disconnecting the radiators on one floor (if they are all piped independently to the basement main) from the supply and installing a new main for that floor may be the easiest.

To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected.
 
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Old 10-23-08, 03:08 PM
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I will get pictures together asap. However it may take a few days. Thanks guys. Stay tuned.
 
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Old 10-23-08, 03:57 PM
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It sounds like you have system bypass instead of a boiler bypass. A large water volume system should have a boiler bypass installed.
 
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Old 11-01-08, 01:16 PM
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Pictures

Sorry this took so long guys. I tried to detail the pipes the best I could. And sorry for all the back round clutter. My mother is a bit of a pack rat.

http://i412.photobucket.com/albums/p.../Untitled3.jpg

http://i412.photobucket.com/albums/p.../Untitled2.jpg

http://i412.photobucket.com/albums/p.../Untitled1.jpg

http://i412.photobucket.com/albums/p...s/Untitled.jpg

Let me know if the links don't work. Also, the boiler is a Weli McClain HE-5 boiler. Series 3. 133000 Btu/Hr in 109000 BTU/Hr out. Something I forgot to state last time was that this is a high effeciency boiler. You can't tell in the picture, but this boiler is exhausted into the chimney. Is this correct for a HE boiler. Also, by plan for the zoning is to eliminate the third floor zone. As it is now when the heat is on for the 1st and 2nd floor is gets really hot upstairs with out even turning that zone on. So my plan was to elimnate this zone. Let me know what you guys think about rezoning the 1st and 2nd floor. My thought was that I just plumb the new main and return for the second floor to the circulator for the 3rd floor now? Should I leave the current main how it is for the first floor? Should I plumb in a boiler by pass? Do I really need a bypass if it is an HE boiler?

I was over at the house two nights ago and collected some data that I thought would help you experts determine if this system is "high mass" or not. As stated above, it is an HE 133000 BTU/hr input boiler. The outside temp was approx 45F. I set the thermostat for the down stairs to 72F. The boiler turned on and did its thing. I set the boiler to 145F. It took 52 minutes for the water temp to reach 145. Not sure if you can see it, but the thermometer I was reading is right behind the red circulator pump in the picture. Not sure if this is the return or supply water temp. Not sure if any of this helps with out the heat loss and radiator output numbers but... Its what I could record on the quick.

Thanks
 
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Old 11-02-08, 05:52 AM
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Maybe I missed it but I don't se a bypass. With the water volume in the system and water content of the boiler the boiler cannot efficienctly heat the system. You need to send some of that water around the boiler and back out to the system.
Bypass_Piping_Explaination
 
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Old 11-04-08, 07:09 AM
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Understood. There is currently no by pass in the system. When I empty the system to redo the plumbing for another zone, I will plumb in a by pass. Should I do a boiler by pass or a system by pass?

Also, what is the best way to zone this system. Should I leave the downstairs radiators on the large 3" main and add a 1" main for the upstairs zone? Or should I get rid of the 3" main and go with something smaller? What would be the ideal pipe size for the new upstairs zone?
 
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Old 11-04-08, 02:25 PM
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Without knowing all the particulars I would say make the basemeint zone independent with it's own main pipe and of course it's own zone.
Make the bypass a boiler bypass if you want to get hotter water faster at a fuel savings.
 
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Old 11-05-08, 06:12 AM
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OK. Boiler bypass it is. But what do you recommend for the mains. I need to run a new main for the 2nd floor zone. Like I said, the 2nd floor radiators are feed with 3/4" supply and return lines off the 3" mains now. The first floor radiators are feed with 1" supply and return lines off the 3" main. What should I do with the 3" mains. Should I leave them for the 1st floor zone? Or should I reduce the size of them???

Also, where should I put the expansion tank and air eleminator. If you look at the pictures now, are they in the correct location.

Thanks
 
 

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