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Adding hydronic fan coil to radiant system.

I've had finned tube baseboard heat in my old drafty house for 20+ years now. Heat provided by outdoor wood burning boiler. Actual old Kewaunee steam boiler. That is the main source of heat. I heat DHW in a Superstor unit. It works great, too. There is a Munchkin for backup in case of outdoor problems. I had no other source for heat other that this fintube baseboard. All the plumbing for this system is in the basement. Also in the basement is the Munchkin.

Cooling in summer is ancient Fedders 18,000 btu window unit. It works good, but is inefficient and leaks cold air in the winter. All in all, I have a sub-optimal system.

So, I broke down and had a contractor friend install me a forced heat/air unit, and I bought a hydronic heating coil (with 1" inlet/outlet) for him to place in the sheet metal duct work he built, because I still want to take advantage of the hot water boiler outside. One of these years I may not feel like cutting wood, so scorched air it will be. Canned the Fedders, too.

My question is about how to be sure I get all the air out of the system if and when I get it plumbed.

I've included a photo with colored lines overlaid to show where I'll be running the plumbing, and I put a big question mark where I think would be the ideal place to put an air separator.



There is a Spirovent in the basement on that plumbing, but that won't do any good for air that will inevitable make it's way up to that coil.

Should I put it in the horizontal supply as it makes it way across to the coil? That makes the most sense to me.

I'm going to be using that 1" rigid Pex (vs. coiled) and sharkbite fittings to plumb this in this area, but down below I'll probably use coiled tubing.

Give me some pointers, if you would... please.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    A critical question. Is this going to be under some pressure? Because for an air separator to work at all the piping has to be under some pressure. But... if it's under enough pressure, an air separator near the pump is going to work better, and once you get that high point purged it should stay that way........................
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JoeKansas
  • JoeKansas
    JoeKansas Member Posts: 14
    ...and by "vent", I'm not particular~ Spirovent or Caleffi or whatever...
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,477
    edited December 2021
    There is a physics principle that addresses how Air is Dissolved in Water. It is called Boyle's Law and it has to do with air molecules dissolved in water. I like to think of it as the opposite of relative humidity. Like water is dissolved in the air (we measure it as relative humidity) Air molecules are dissolved in water. By placing the micro bubble air separator in the proper location, the system actually removes microscopic amounts of air from the system and vents it out. Over time all the air can be eliminated.

    The principal of this phenomenon is explained in Dan Holohan book available on this site or Amazon. The book is titled Pumping Away. This is why a Spirovent (or whatever) in the basement is able to take air out of a 2 or 3 story system. So, as @Jamie Hall said, Just get most of the air out of the Hydronic coil so the water flow will entrain the air that is left, and over time the existing Spirovent (or whatever) should do the job.

    Respectfully Submitted
    Mr.Ed
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    JoeKansas
  • JoeKansas
    JoeKansas Member Posts: 14
    Well, as far as pressure is concerned, just the static head pressure from the mass of water out in the boiler. The coil is situated, roughly, about 6 foot higher than the top of the boiler outside, and the plumbing for the rest of it is in the basement. So, the coil is probably 9 feet higher than what it's connected to there.

    I'd have to "power purge" the air from the coil, I'd think, but once the thing filled with water, no air should get in there. Do these "vents" prevent a vacuum from drawing air back in if the water level was to drop?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,477
    edited December 2021
    As long as the system is piped properly and you have at least 12 PSI static pressure, there will be no vacuum. Pressure is the opposite of vacuum. If the highest pipe in the system is less than 15 feet above the place where the pressure gauge is, then you will never get a vacuum anywhere in the system.

    @JoeKansas said: Do these "vents" prevent a vacuum from drawing air back in if the water level was to drop?

    That answer is NO but it don't matter. Just keep the pressure at 12 PSI on cold start up.

    Do you already have a Spirovent (or whatever) on you system? If yes... then all you need is a coin air vent at the top of the duct coil.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    JoeKansas
  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    JoeKansas said:

    Well, as far as pressure is concerned, just the static head pressure from the mass of water out in the boiler. The coil is situated, roughly, about 6 foot higher than the top of the boiler outside, and the plumbing for the rest of it is in the basement. So, the coil is probably 9 feet higher than what it's connected to there.

    I'd have to "power purge" the air from the coil, I'd think, but once the thing filled with water, no air should get in there. Do these "vents" prevent a vacuum from drawing air back in if the water level was to drop?

    No. The vents do not prevent a vacuum -- which you will have -- from drawing air back in. In that piping arrangement, you will need to make certain -- doubly certain -- that all the piping above the boiler water line is not only pressure tight, but is vacuum tight, which is far harder to do and not the same thing at all. If you do not, you will have endless trouble with air getting into that coil. Note, by the way, that sharkbite fittings will not seal against a vacuum, and are unusable in this application. Crimped fittings almost always will. Do NOT put any form of air removal gadget on the system anywhere above the boiler water line.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JoeKansas
  • Zman
    Zman Member Posts: 7,542
    A heat exchanger on the OWB is a good idea if you have heaters above the boiler. That way the heating system does not suck air back in a get airlocked. The other components will also last longer in a pressurized O2 free environment.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,477


    You just don't need 2. You don't need a separate one for the Duct coil.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    JoeKansas
  • hot_rod
    hot_rod Member Posts: 21,793
    Caleffi has anti vacuum caps for our air vents for those applications. If it is an open system with the coil above the boiler you can pull sub atmospheric conditions at high temperature.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    JoeKansasSteamthemean
  • JoeKansas
    JoeKansas Member Posts: 14
    Zman said:

    A heat exchanger on the OWB is a good idea if you have heaters above the boiler.

    Oh, hell, I left that part out. The OWB and the radiant system are separated by a heat exchanger. Sorry I didn't explain that.

    Water from the OWB circulates in a loop through the heat exchanger and back outside.
    The Superstore is in this same loop. I did that because I keep that OWB hot year round (burn wood from a sawmill. Inexpensive, so I have unlimited hot water all year.)
    My reason for doing that was because in the summer, the pump that circulates the OWB water through all this~ I operate it off a 15 minute timer. When I want to heat the tank back up, I just spin the knob... the pump runs for 15 minutes and heats that tank right up, then the pump shuts off.



  • Zman
    Zman Member Posts: 7,542
    In that case, a simple air vent would work where you are suggesting.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    JoeKansas
  • EternalNoob
    EternalNoob Member Posts: 42
    Jamie, care to elaborate on why a vent above the boiler is a bad idea?

    I have been under the impression that extraneous air release valves can be sprinkled around like salt and pepper, the more the merrier, but what do i know. An air release at that location might not be necessary but would make the initial filling of the coil easier.
  • Jamie Hall
    Jamie Hall Member Posts: 22,877

    Jamie, care to elaborate on why a vent above the boiler is a bad idea?

    I have been under the impression that extraneous air release valves can be sprinkled around like salt and pepper, the more the merrier, but what do i know. An air release at that location might not be necessary but would make the initial filling of the coil easier.

    If -- and only if -- the valve can seal against a vacuum, yes one can sort of spray them around. However, if you have a situation where some of the piping may be in a vacuum from time to time, such as above the water line of a boiler at atmospheric pressure, then if the valve is not tight against a vacuum, it's going to leak air in. Maybe not all that much, but some. And that you don't want.

    This is not to say that there aren't situations where an air release isn't warranted at a high point. I've specified and had installed quite a number of them. But only in situations where I am trying to fill a pipe (or pipeline!) and normal residential type purging won't do -- and, most important, where the line under all normal operating conditions will be well above atmospheric pressure at that location.

    In your specific situation -- filling that coiil -- it might be advantageous, but I would prefer to use a valve which, once the coil was filled, I could close and be sure that it would stay close -- like a quality ball valve.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,542
    With the exception of very large sprawling heating systems, remote air vents are usually not necessary and frequently leak. If the system is piped so it is "pumping away", has a good air sep, and well laid out purge points, remote air vents are not needed.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • TheGerman
    TheGerman Member Posts: 3
    A good rule for piping is "In the bottom and out the top"
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,295
    No. As far as flow through the coil is is better to go in the bottom and out the top for air removal only however,

    the coil will not transfer heat as well with this particular coil.

    You always flow the water counterflow against the air flow.

    In this case the air flow is going up so the water flow should go down with the water inlet at the top.

    It is not a killer on heat but on chilled water it is for sure

    But the water in should go in the top