Holohan's Hydronic Forum: A Special Section Sharing Exchanges Between Dan And His Fans.

Where's The Tank?

I've got a job to replace a gravity hot water boiler in a large residence. There is nothing wrong with the current system, but the customer wants a new boiler anyway. I've searched high and low for a boiler with a 1,500 square-foot output and five-inch tappings, but I've been told there is no such thing. This beauty has two, 4-inch feeds and two, 4-inch returns. I figured to replace it with a nine-section Peerless and two, 2-inch pumps. The problem I'm having is I can't find the expansion tank. My take is that there is an atmospheric (open) tank in the attic, but I have yet to find it. I can't plot out my "Pumping Away" piping without it. Any ideas?

Dan replies: There were many gravity systems with no tanks. I've seen them, and I have to admit, they will make you scratch your head at first. The Dead Men fed the radiators on these jobs bottom-to-bottom, and they kept the tops of the radiators filled with air. Keep this in mind when you're refilling the system. As for Pumping Away, this type of system has multiple compression tanks (each radiator becomes one), so the point of no pressure change will locate itself somewhere in between all of them. Eventually, the air will be absorbed from some of the radiators and vented from the system. Just pump toward the radiators. And don't worry, these gravity systems play by different rules.

Sometimes The Boss Is Right

I work for a contractor who insists on putting the expansion tank upside down on the return header on all our new boiler installs. He also insists on putting a ball valve between the return header and the expansion tank. I'm positive installing a valve there is not the right thing to do. Is there a rule, law or code I can refer to in order to show my boss that it's not only an unsafe practice, but also illegal?

Dan replies: The tank should be upside-down according to the manufacturers, and the system works best when the tank is near the suction side of the circulator. A valve between the tank and the system allows a service tech to check the tank's air charge without having to drain the system. Unless it's prohibited by a local code, I think it's a good idea. If you're afraid someone might close the valve, you can remove the handle. If the valve does get shut, the relief valve will pop. Sorry, but I'd agree with your boss on this one. You should never stop asking questions, though.

A Homeowner's Dilemma

I'm trying to decide whether I should (and how I should) upgrade my home heating system. I currently have a 1977 oil-fire boiler (244,000 MBH input) with one-pipe steam to the radiators. This is old stuff. The house is about 2,800 square feet. I've been told that a two-pipe upgrade to the radiators would help with the low efficiency, but I wonder by how much. Will it be 10 percent or 20 percent?

Also, my radiators have bottom input/output ports. I could use both ports. That is, if I could get the unused one out!

Lastly, I acquired a gas furnace (forced air, high efficiency) last year for free, and I now have that option as well. I've had a test run on the house and the 120,000 Btu/hr. gas furnace would be just enough for the house with a little to spare.

I think the gas would cost less to run, but I'm concerned that it may be less comfortable and might cost more to change the system. I've also been told that I'd be sorry if I go to forced air.

The system now uses between 1,800 and 2,000 gallons of oil per heating season. It's done this for three years running. I've been paying the bills.

Dan replies: You may have steam radiators. These have push nipples only across the bottoms of the sections, and they don't easily convert to hot water. You can save fuel and get the most out of a new steam boiler, but only if you can hookup with a contractor who understands steam. If you go with the furnace, you'll have to run ductwork around the house. I'm not sure how you'd like the looks of that. I'd like you to post this question on the Wall, which you'll find at my Web site (www.holohan.com). That way, you'll get more opinions from heating professionals. You might even meet someone in your area to help.

Too Much Element

I looked at a problem baseboard job last night. It is a gas-fired system with three zones, using cheap no-name zone valves. The problem lies in the bedroom zone. As you would expect, one end of the zone is warm enough to overheat the place, but the tail end is, well, cold. It's a simple case of too much radiation on one zone. In addition, all the between-radiation piping in this series loop is done in (can you believe it) in 1/2-inch copper, with 3/4- by 1/2-inch elbows at each baseboard section. The guy must have saved maybe $50 on the job!

You said at your seminar, the right way to cure this is to split the zone into shorter loops. Sadly, the general contractor who hired this so-called heating guy completely sheet rocked the basement ceiling, so piping access is nil.

Other than just playing with the baseboard dampers, is there anything else we might try? Additional pumping capacity? Anything?

Dan replies: Try raising the water temperature. That will overheat the front of the loop even more, but it's about all you can do under the circumstances. And keep in mind that this is one of the reasons why God gave us jackhammers and chain saws.

Hopelessly Seeking Help

I'm still trying to get someone to straighten out my system. We now know that something is still keeping steam from circulating past the middle of the house, even though the system is running at 7 psi. I know that the system should never have to use that much pressure.

The last guy I called for help is an old-timer. He said what he would do is install a condensate pump and remove the Hoffman Differential Loop completely. He surmised, as you also had surmised, the Hoffman unit was probably hopelessly clogged.

Does this sound like a viable solution, or is it just a theory that could leave my system hopelessly bastardized?

Dan replies: Before I did that, I'd have them fix all the radiator traps, put a good main vent at the end of the dry return (in place of the Hoffman No. 15) and run the system on very low pressure by using a vaporstat. If that doesn't work (and it just might), I'd have them install the condensate pump. You're going to have to fix the steam traps before the pump goes in anyway, so this is a good first step. Good luck!

How Big A Boiler?

Let's say I'm measuring a home for a replacement hydronic boiler. It might have five zones, and the total Btu/hr. load for all the radiation (baseboard) is a certain figure. Is there a multiplier or a percentage off the total load I can deduct, since all five zones will rarely be calling for heat at the same time? Or am I just asking for trouble?

The reason I'm asking is because I just told a homeowner he needed a certain size boiler for the given load. He told me he wanted the same size that originally came with the house. I told him, since he had added additional zones installed during the past 35 years, the original boiler was no longer the proper size. Needless to say, he went with the guy who read his existing ratings label on the 35-year-old boiler, and replaced it with the same size. The boiler I had proposed was about 25 percent smaller.

Dan replies: I don't think it's a silly question at all. In fact, I think it's something more people in the trade should be asking. I've never seen anything official on this, but I once met a guy who regularly deducts 10 percent per zone, up to 30 percent of the total load, and he has never had a problem. I believe him, and I think you're on the right track. And don't get frustrated. You're never gonna sell 'em all!

Vents On Two-Pipe Steam Radiators?

I am working on a two-pipe steam system. I am trying to eliminate all the noises in the system. My question is this: Is it OK to put air vents on the radiators? All the steam traps have been changed (there were 32 of them). Will insulation make a difference in the noise?

Dan replies: You don't need air vents on two-pipe radiators. If you put them there, they'll mask bad steam traps and create problems with the system. As to the insulation, yes, you're better off with it. It keeps the steam from condensing too quickly in the mains and allows the steam to travel further. If the mains are uninsulated, excessive condensate might cause noise, but you'd also have to have bad pitch, wrong pipe size and factors such as that in the mix as well.

Same Guy, Next Question

Thanks for answering me so quickly. I have a follow-up question. Can you please explain what problems can occur if I put air vents on the radiators? I was told, if I put air vents on the radiators it would add a little humidity to the house.

Dan replies: A two-pipe radiator usually has a steam trap. The air is supposed to move through the trap and leave the system through a main vent near the end of the dry return main. The Dead Men did it this way so there would be no odor of steam in the rooms, and also to prevent vents from squirting dirty water on the walls or curtains.

When a steam trap fails, some of the radiators get cold, because steam enters the return lines and prevents the air from leaving the system. That's when you know it's time to fix the traps. Steam in the returns leads to water hammer, uneven heating and system damage.

If you put air vents on two-pipe radiators, the air will have a way out - even if the traps should fail. The radiators will get hot and fill with condensate. The condensate can't leave the radiators because there's steam in the returns. That leads to squirting air vents and water hammer. Meanwhile, the boiler runs out of water and shuts off on its low-water cutoff. If there's an automatic water feeder, the boiler might flood when the condensate finally returns at the end of the heating cycle.

Better to do it the way the Dead Men intended. If it's humidity you're after, put a pan of water on the radiator. That's what they did in the old days.

Hope that helps!