View Full Version : Consequences of removing basement heat exchangers on a FHW system?
12-23-2010, 02:45 PM
I recently purchased an 1800 square foot house built in 1950 with a FHW by oil system that takes an extremely long time to get up to temperature... like 3-4 hours or more. The house has one single zone/loop. The radiators on the upper floors never really seem to get hot, just warm, even at the supply/inlet pipes... especially on the 2nd floor.
I can't use my programmable thermostat because it takes so long that it never reaches the higher target temp. I just leave it on HOLD at a higher temp which is not very efficient. The system was cleaned and tuned up last spring by a professional and the circulator pump seems to be working fine.
I'm going to replace the oil boiler with a high efficiency gas boiler in the spring/summer. I would do it sooner, but the city will not let the gas company dig up the street during the Winter months.
The heat exchangers (radiators) in the finished basement are some clamp-on finned things which are intermittently attached to the heat loop pipes near the ceiling. I don't care about the heat in the basement as we don't use it as living space.
Here are my questions:
If I remove the finned heat exchangers from the pipes in the basement and put pipe insulation on them, will it direct more heat to the upstairs radiators making the rooms that we use warmer?
Could there be some kind of unintended consequence due to insufficient heat exchangers in the system?
Any other issues I should be aware of before proceeding?
12-23-2010, 04:20 PM
Before you start taking things apart, tell us what the boiler supply and return water temperatures are. You may need to just raise the supply temp. In an uninsulated floor, adding heat underneath will send a lot of it upstairs anyway, so disconnecting may not buy you much. Also, keep in mind that (assuming the system can keep up), a boiler is most efficient running constantly and just meeting the house needs. Short cycles waste a lot of energy. It sounds like your system does not have much reserve, or is not setup to provide the heat you need (if the supply temperature is too low), and it can't keep up, or has no reserve. On a typical older, non-condensing system, you really need the return temp to be above 130-degrees.
12-23-2010, 06:25 PM
I'm new here so take what I say with a grain of salt and wait for some other replies. I agree with jadnashua and not disassemble anything yet. Since this is a new house you might not be completely familiar with your system. It could be as simple as a flow issue. Assuming your pipes aren't clogged, did you check you circulation pump? Even if the motor is running older pumps had a spring coupling, usually visible between the motor and the pump head (between the pipes). If this is broken your system might just be supplying HW via gravity alone. The springs do fail under normal use but will definately break if the pump head is seized. With your system turned off at the emergency kill switch you may safely be able to turn the pump side coupling by hand.
Safe to assume you bled the air out of your system system? The radiators should have a bleed valve installed on top. If they are not slotted you may need to get a "key" at the hardware store. Even if water comes out right away doesn't mean your pipes aren't air dammed. With your system and circ. running continue to bleed out water and listen for air moving through your pipes. Start with the radiator furthest away from your boiler. If it was air hopefully the bubble will make it up to and be trapped in one of the radiators and again bled off.
You will need to replace the water removed with make-up at the boiler. In your case I would probably do this when your system is cool. It should not take much and the amount is set by the pressure gauge. Measure the vertical height, as best as possible, from the gauge to the highest point in your system. (If the boiler is in the basement and you have 8 ft. ceilings, this will be about 16 ft. but measure anyway) Water has weight that will exert pressure on the gauge at the ratio of .433 psi per ft. of water. For a 16ft water column the minimum system pressure would be about 7 psi. It is typical to set the system at about 12 psi to help the air stay dissolved in the water to be dealt with by additional components installed on the system such as air scoops. These remove the dissolved air mechanically and transfer it to the expansion tank, if your system has one althoug these can become water logged.
I hope your problems are this simple, as these are easy fixes. If you are not familiar with hydronic systems, you may want to hire an HVAC tech to go over your system with you and show you what components are where and how they operate. Talk to neighbors and friends to get recommendations for local contractors, find a good one and stick with him. Upgrading to a hi-eff unit is not as simple as swapping out the boiler. There are a lot of subtleties that can make a system operate so-so and not provide you with the best efficiencies possible. That comes from proper design and installation that best matches it to your system. Good luck.
12-23-2010, 08:05 PM
Thanks jadnashua. How do I measure the supply and return temps? A thermocouple on the surface of each pipe, or do I need to measure the temp of the actual water flowing through by tapping the pipe somehow? Do you know if there is there a practical convention for measuring this?
The boiler temp (from the gauge on the boiler) is around 145 degrees Fahrenheit when it has been running for awhile.
Thanks too chris24. I don't hear any sign of air in the system, but I'll bleed anyway. I'll check the circulator pump coupling again too.
I have a licensed plumber I use who will put the high efficiency boiler in. He has converted two steam boilers in a rental property for me already which work flawlessly. He is as smart as anyone I have met and does quality work... a bit pricey, but worth every penny!
At the same time I believe in DIY. That is how I learn. I'm hoping to solve this one on my own if possible.
12-24-2010, 09:38 AM
Often, when installing a boiler, they'll install (or they are part of the boiler) a temperature gauge on both the supply and return. The one on your boiler is probably the supply temperature and at 145-degrees, is probably 30-40 degrees too cool...raise it to say 180 and see what happens. On that type of boiler, the return temperature could be below 100 with that supply temp, and will cause problems, rusting out the boiler way prematurely, and, with the supply only 145, probably not enough heat each cycle to make the house warm. If your boiler could tolerate it, 145 might be a good supply temperature to maintain the heat on a moderately cold day, but that would only work with one designed for it...yours isn't.
A thermocouple, or even an oven thermometer, if you put it in contact with the return pipe and insulate it will give you an approximation. The better choice is to install an immersion gauge on a T somewhere near the boiler for permanent use.
If the water temperature from the outlet of the boiler up to the first radiator is the same, the circulator is probably working, but air trapped anywhere in the system can prevent it from circulating throughout the system.
12-24-2010, 09:35 PM
Okay... so I did some more research and thinking. Thanks for the suggestion of not taking things apart. I now realize that the boiler is probably adequate to heat the whole house including the basement. Something else was the problem.
I discovered that the pressure in the system was only about 2 PSI. I actuated the purge lever on the (12-15 PSI) Watts regulator for the auto-fill. It freed up the regulator and the system bumped back up to 15 PSI. I bled the air from the system and went around to all the radiators and vacuumed out the fins to improve heat transfer. The system is definitely running better and more consistent between the first and second floors. I have seen the boiler temp over 150 and closer to 160 degrees F.
Would 180F be a standard boiler temp for a ~30 year old boiler/FHW system? Would that be specified in the boiler manual (that I don't have) or would this boiler probably work for a range of temps depending on application? Basically I'm asking how I determine the optimum temp to set the boiler.
12-25-2010, 05:03 AM
As you tell that this is new house the problem may be that you don't know the system well. So don't be fast to remove it. Boiler is what meet with the housing needs. I agree with jadnashua.. I am using the FHW system from last 4 yeas for my 2000sq ft house and it work great.
12-25-2010, 07:25 AM
With only 2psi, the safety circuits in the boiler should have prevented it from even firing! On a non-condensing boiler, the return temperature is more critical for longevity than the supply - the supply has to be high enough for the return to remain above 130-degrees; that's why a thermometer on the return is so important. Since the system is under pressure, just like your auto, it can support temperatures that get moderately high. 180-190 are not uncommon. Adjust it to where you get the desired long-term comfort, minimizing cycles, and keeping the return above the 130-degree critical minimum (it's okay if it drops below for a short time, but this should be minimized). You can set the high limit anywhere within reason to get the heat in the house. It won't let you set it too high (generally), and that number will be shown in the manual.
Air trapped can and will prevent the water from circulating properly. You may need to go around and purge again as the pump moves things. Once fully purged, unless you have a leak, you should be fine for the season.
12-29-2010, 11:54 AM
System is running much better... Thanks jadnashua. I bumped the low temp on the control to 180°F and left the high limit at 200°F, maintaining the 20° differential required on the warning label. Now the system gets the house up to temperature much quicker.
The circulator and burner rarely, if ever, seem to run simultaneously. I understand that the burner runs until the boiler reaches the minimum temp, then it shuts off and the circulator kicks on to send the hot water around the house to the radiators... but it seems that the circulator then turns off and the burner fires up again to bring the boiler back up to the minimum temp. I've been looking in on the boiler several times per day for a couple weeks and I have only once observed the circulator and burner running at the same time. I would expect that the circulator would still run while the burner was running to maintain the temp.
Any idea what the relationship should be between the circulator and burner? Is it common for them to run opposite one another?
I'm still toying with the idea of removing the finned exchangers and insulating the pipes in the basement loop. The basement warms up very quickly, the 1st floor a bit more slowly, and the 2nd floor is always the coolest. There is only one loop in the system which runs around the perimeter of the basement near the ceiling and all the radiators (to the 1st and 2nd floors) are individually tapped into this loop. It seems to me that removing the fins and insulating the pipes will prevent the heat from escaping into the basement (that we don't use for living space) and keep the water hot until it reaches the radiators in the 2nd and 3rd floor living areas. One concern I have is that the only thing directing the water to the upper level radiators is the equalization of the pressure caused by the circulator and the path of least resistance. A portion of the water just circulates around the simplest part of the loop (the perimeter of the basement) and then returns to the boiler and if I insulate the pipes it seems that some of the water will return to the boiler nearly as hot as it left. Maybe this is no big deal as it again leaves the boiler and goes out around the loop, some to the radiators.
Any thoughts on this?
I figure the fins can be re-attached and the insulation removed if it doesn't work out... I just don't want to stress the system or make it less efficient by reducing the amount of heat exchange. In theory, if I took out all the exchangers and left only insulated pipes, the boiler would get up to temperature, the burner would turn off, and the circulator would circulate the water continuously, for a really long time, until the temperature finally dropped low enough for the burner to fire up again. Seems like removing the fins/insulating the pipes would reduce the amount that the burner fires (saving oil) and direct more heat to the desired areas and less to the basement making the system more efficient.
See any holes in my theory?
Thanks again for your help!
12-29-2010, 04:33 PM
You may need to add (or find, if they are there) some valves to balance the flow so you get the hot water where you want it.
The boiler and the circulator are controlled by two different things. When the boiler turns on, it runs until it reaches the high limit. It then waits until it drops to or below the low limit to turn back on again (mod-con type boilers may let the water cool off if no demand for heat, and are often set up differently). The circulator is connected to the thermostat, and will turn on when the thermostat calls for heat, and off when it doesn't. Often, providing the heat will cause the boiler temperature to drop, and then it will come on, but these things are independent. Some boilers run on a primary/secondary loops system, and there is a circulator for each loop. On that, the primary loop circulator is timed with the boiler's burner.