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Cold start an oil fired water heater??

Interceptor Member Posts: 46
Can a 32 gallon center flue hot water heater be repeatedly cold started without doing any damage?

The water heater is used for radiant floor heating. There is no DHW on this system. A Tekmar 363 provides outdoor reset on the system loops. I would like to let the 363 control the burner and let the water heater temp drop as low as possible to reduce stack losses, then run it up to 130-140 when it fires to burn off any condensation.


  • billtwocase
    billtwocase Member Posts: 2,385
    water heater

    They are for domestic water heating. This should not be used for heating space. Cold starting it will also shorten it's life
  • icesailor
    icesailor Member Posts: 7,265
    Cold start oil fired WH's:

    I can not impress enough on you what a bad idea this is.

    Back in the mid '90's, when this craze of using water heaters to heat houses and get domestic hot water came around again, Bock Oil Fired water Heaters became a favorite of some in New England. There was a guy in New Hampshire who put in a lot of them. They all failed within two years. Bock wouldn't cover the warranty because that is not what they are approved for. This one person in New Hampshire (who I don't know and don't know his name) moved to where I work in Massachusetts. He sold a lot of jobs to the hot shots with the same plan, Bock oil fired water heaters for heat and water. He had the same results. The water heaters just couldn't take than cold water flowing in from a system like that.

    My wife and I went to a farm in Warner, NH and when the owner found out where we were from, and I worked, he asked me if I knew ths guy who had installed this system in his house, went through three Bock water heaters and wouldn't return his calls. Then, the owner had to re-do his whole system. I don't know anything about the installer. Just his problems.

    I have had experience with this bad idea. It goes back to before you probably knew what heating pipes were. Like very early, 1960's. It was sold as a way to heat a cottage in the spring and fall. The first thing one noticed after a few years was yellow hot water when the tank was breaking down.

    Water heaters heat domestic hot water,

    Boilers heat heating water.
  • meplumber
    meplumber Member Posts: 678
    I agree completely.

    Like the Ice-man, we had the same problems up here in Maine.  Again, Bock said no thanks, they are not approved as such.

    You are asking for more problems than it is worth. 
  • Steamhead
    Steamhead Member Posts: 16,886
    Part of the problem then

    was that oil-fired boilers weren't being made small enough for these loads. That's starting to change. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Interceptor
    Interceptor Member Posts: 46

    The system in question is already installed and running (for 10 years), but without outdoor reset. I was just wondering if I could cold start it to possibly get some fuel savings. Right now I just leave the aquastat at 130. It's an Aero (Bradford White) CF32 water heater heating my 1500sf work shop with radiant slab. It's been in this system for 10 years, and I bought the water heater used so who knows how old it really is. I'm almost ashamed to say this, but it has not been cleaned since I installed it. It has been trouble-free except for a leaking oil pump on the Carlin burner. It's a closed system, no domestic hot water. It will be difficult to convince me that these things don't hold up for heating, my (limited) experience tells me otherwise, I am already exceeded the warranty period by 2X plus however many years the previous owner put on it. I know 10 years is nothing in terms of boiler life, but until it fails I'll stand by it, and I'll probably replace it with another when it does fail.

    The Giant OG32 is manufacturer approved for space heating or combination heating/DHW.

    The Bradford White Combi2 is another one, though that one does have a separate coil in the tank for space heating, so it's a bit different.

    A cut and paste from the OG32 manual:


    As moisture from the products of combustion comes

    into contact with the cold surface of the inner tank, it

    may condense. This situation will usually occur:

    1) When the water heater is filled with cold water for

    the first time.

    2) If the water heater has been undersized.

    3) When large amounts of hot water are drawn from

    the water heater in a short period of time and the

    refill water is very cold.

    Due to the high-efficiency rating of this oil-fired water

    heater, it may produce more condensation than older

    models. This condition is not uncommon and must

    never be misinterpreted as a leaking tank. It will

    disappear once the water becomes heated.

    That's not to say that condensation is good for it, but I thought that as long as the condensation is burned off within a few minutes it wouldn't cause any significant damage. The water heater can go from cold (60 degrees) to 140 in about 14 minutes with no draw. I guess I'll just forget about cold start, the savings are probably minimal anyway. But I'm not giving up my water heater until you pry it from my cold dead hands.
  • i thinx maybe if

    the condesation is a result of air flowing thru the tank from the gun's air intake & out the chimni, unless the barodamper allows air in to condense down? Either case an electric damper coordinated with the gun & close when the gun aint firing thus minimizing airflow & standby heatloss,& keep the tank hotter?
  • icesailor
    icesailor Member Posts: 7,265
    Cols Start Oil Fired WH:

    It sounds to me like you are using the oil fired heater as just a heat source for a shop. That's different than what I was writing about.

    I'm writing about heating a large space, with potable hot water where you must (to be legal by code) use Fin Tube baseboard with Type "L" Copper fin tube and all the tube in the system must be Type "L". Then, you have a few baths and a kitchen to supply with domestic potable hot water. Then, you shove a heating load upon the whole mess. It is extremely hard on the water heater. And often (as a customer told me the other day about her system) you can't take a shower when the heat is calling.

    But in my 40+ years of doing this, all the ones I ever saw where they used an oil fired water heater as a primary DHW supply AND a primary heat source, the failure rate came quickly and never worked well. The first sign of failure was rusty water after long periods of no use.
  • Interceptor
    Interceptor Member Posts: 46
    Did you read it?

    If you go back and read my original post I think I was quite clear about

    the basic application. Radiant floor heating with no domestic hot

    water, that's what I said.

    The water heater is firing at the lowest recommended rate for the

    burner, a Carlin EZ-1 with a .50 nozzle. This was done to increase the

    run time because it was short cycling with the standard .75 nozzle. It

    is certainly not overworked. When the system is stabilized the return

    water temps are typically 20 degrees below supply, I don't know how that

    can cause stress on a water heater designed for 50 degree inlet temp at

    higher flow rates. Worst case is at startup when the slab is cold and

    return water is somewhere between ground temp and ambient, but that's

    still no worse than a couple showers with 50 degree inlet temp, and it's

    not outside the designed operating range of a water heater. These

    things are designed to deliver nearly endless hot water from 50F inlet

    temp. They are designed to handle stresses that no cast iron boiler

    could ever handle. Maybe not built to last as long, but seems to me they

    are better suited for low temp radiant. Whether the system meets code

    requirements or not does not concern me. It's perfectly safe, and resale

    value is not an issue.

    My home is just 1100 square feet. It also has radiant floors but uses a

    cast iron boiler for heat source. The system was professionally designed

    and installed when the house was built. There are major design flaws

    throughout the entire system, and if I'd known better at the time I

    would have made them correct it. I had them out a few times in the

    beginning but the techs seemed to know less than I did at the time and

    the system has never worked properly. Despite being considerably smaller

    with 4 feet less ceiling height, the house uses 2 - 2.5 times more fuel

    annually than the shop. That's what I get for trusting a professional

    to do the job. I'm sure he had 40+ years experience too. I work with a

    bunch of guys like that, lots of experience but no real knowledge. Set

    in their old ways with no capacity or desire to learn or accept new

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I'm sure he had 40+ years experience too.

    I do not know about the heating business, but in the computer programming business I met someone who had 20 years experience in the same way. She was the most incompetent programmer I ever met. She said she had 20 years experience, but actually, she had 6 months experience 40 times. She had learned nothing from that experience.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Old ways are not the issue

    the old ways are not the problem, total lack of understanding of how systems run is the problem. The old coal systems needed to be efficient as no one wanted to shovel more coal than they had too. I often find it is the half/hearted knowledge that is messing up systems. I think you may need a real professional to look over your house system to get it right.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Interceptor
    Interceptor Member Posts: 46
    Old School

    You're right Charlie, the old guy probably installed crappy systems 30-40 years ago too, but oil was 80 cents a gallon so nobody cared or even noticed as long as the house was warm. Now with oil near $4 per gallon it's no longer good enough, and the old guy is too stubborn to change his ways. That's what I mean by old ways. He says if it has worked this way for the past 30 years it must be the best way. He's wrong. He was wrong the whole time, but nobody noticed. On top of that there have been advancements in electronics and even combustion techniques that allow better control and efficiency. Homes are tighter and better insulated. Some guys can roll with the changes, others will spread their stupidity upon unsuspecting homeowners like me. I will never blindly trust another professional again, no matter how many years experience. In fact I disregard anyone's boasts of having lots of experience. Experience is nothing without current training and willingness to progress with technology, even in a field where technology progresses very slowly.

    I'm replacing the entire heating system in the house this summer, including the underfloor PEX. I will be doing most of the installation myself and a friend who is a HVAC professional will make the final adjustments. I am also installing a 384 square foot solar thermal array which is the reason the heating system is finally getting upgraded. The radiant currently requires 170-180F to keep the house warm which won't make very good use of solar. If I can get my temp requirement down to 120 or less I should be able to cover a large part of the heating load with solar. There will be times during spring/fall when the oil burner is not required for several days or weeks at a time, but it still needs to be ready to go as backup. That's my reason for asking about cold start. It seems foolish to have the oil burner running several times a day to maintain 140F when the system only requires 90-120 degree water that may not even be needed. I'm still not sure if I am going to run a solar loop to the shop, or just the house. I'm not sure what I'm going to use for oil burning in the house. I have a new Giant OG32 water heater that I picked up cheap but I'm not set on using it, I will happily store it as a spare for the shop. I'm considering a small cold start boiler with a storage tank to give it some load. I just discovered the Toyotomi OM-180 today. I already know what kind of feedback I'm going to get on that.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666

    A saying current among some engineres I know goes, "Experience is what tells you you are doing it wrong again."
  • icesailor
    icesailor Member Posts: 7,265
    Old Farts:


    I've forgotten more about building trades than you may ever know. And I've not forgotten much. I see regularly things that I did 40 years ago and am still proud to say that I did them. I and my wife have built more than one house from scratch with myself doing all the mason work, wiring, heating, plumbing and finish work. I framed and trimmed out these houses. Milled my trim and flooring. I regularly get schooled in what is going on.

    If you think I give a rats rectum what you think, sorry.

    I offer suggestions. Based on my long experience in building trades. My love, my hobby and job.

    What you are doing, isn't correct. You can do it. Have on it.
  • Interceptor
    Interceptor Member Posts: 46
    It's not you

    It seems I have offended you icesailor. You must have assumed that one or more of my comments was referring to you. They were not. You must have grouped yourself in with the kind of person I was describing. I never once disputed your intelligence, knowledge, or abilities. I commented about a guy who installed my heating system. If you somehow find my description of him comparable to you, that's on you. I do not know you and therefore I do not comment on your knowledge or skills. It sounds like you've done some great things in your lifetime.

    On the other hand, you don't know me beyond a few words I've typed on these pages, yet you feel that is enough to discredit my knowledge of the building trades as a whole. Shame on you.

    I am here because I assume that there are people here with more knowledge than me. If I didn't value the opinions of others then I wouldn't have come here for advice. The only problem I have with you is that you never even attempted to answer my question. You just went straight to telling me why a water heater shouldn't be used for heating and how it's destined for failure. You went off on combo systems and problems that are not related to my situation (colored water, cold showers). And after all that you didn't even bother to answer my question.
  • icesailor
    icesailor Member Posts: 7,265
    Oil fired water heaters


    You don't offend me. No one does. I answered your questions as best as I could.

    I do mostly service work now. My biggest work comes from being called or having others ask me about things. I could get a call from some stranger, with a problem like yellow water in the tub when they fill it up. I check it out. I see something done recently ( in the recent few years) and I know what their problem is. The customer doesn't tell you that the installer has been romancing them with answers for the last year about the worsening problem. Like a failing water heaters connected to floor heating systems. I get a knot in my stomach when I realize that I will be telling someone they got screwed. The screwed calls up the screw-er and complains when they find out the truth. The screw-er responds with some COS and tell them that I don't know what I am talking about. I'm being bad mouthed behind my back and I can't defend myself.

    Here's what I deal with.

    I went to a home yesterday in a nice development. They had an 80 gallon electric water heater in a second floor closet that was as wide as the closet and the casings and baseboard will need to be removed to take it out. The owner wants an instantaneous gas water heater. I could have put it in the closet but there was no way to run the gas. So, I checked out the crawl space. 48" from the top of the footing to the bottom of the sill. I can get more height by going out with the floor joists being parallel. It had a new 90%+ WA furnace vented a LONG distance with 2" Sch 40 DWV PVC. The outside terminations weren't cemented. No bird or insect screens on the outlet or inlet. The outlets were 2' from the LP gas regulator. Because of windows, doors and framing issues, I had two choices on venting and install location. Under the kitchen in which case, it would vent on to her brick patio where they might be annoyed by noise if it is running. Or, on the west side beside the outside shower but that would put the heater under her bedroom and it might be noisy. If she was fussy about noise, it was a consideration. I then told her that it was too bad that the gas furnace had been replaced by an air-head because the Tank-less I was using had a max. fire of 200,000 BTU's but I would have put an air handler in for the heat and done a Mod/Con wall hung that ran at 95%+ and would have given her all the hot water and heat from one unit. From the look in her eye, I could have sold that easily. I told her of the problems with instantaneous heaters and the thermal lag with short draws etc and they need a small 8 gallon tank to solve this problem that some users have complained about. She now knows all the plus's and minus's to the install. Did I miss anything?

    When I'm done, she will know what to expect.

    I spoke with the manager of the supply house I deal with and he took me to the employee house they have and showed me the one they have, the same as I use. It was extremely quiet. I asked the guy who lives in the room above about the noise through the floor. He said he could barely hear it.

    If you skip a step, you could be sorry. If I skipped a step in telling you to not use an electric water heater, I'm sorry.

    I live by this motto. "There's never enough time to do it right. But there's always time (for someone like me) to do it over."
  • corrosive factor?

    is the condensation as corrosive as the combo of condensation + soot?
  • icesailor
    icesailor Member Posts: 7,265
    Corrosive Factors:

    If you have a cold start boiler, or a boiler that runs for long periods at below the dew point of condensation (like 140 degrees), you get a soot that has a lot of sulphur in it and with the water vapor condensing, you get sulphuric acid. It forms what I call Kibbles and Bits. A black slag like substance that requires a lot of work to remove it. If you have a really clean, smoke free fire, it may be more like a grey, cementious material that is even harder to remove sometimes. If you look at the exhaust venting (smoke pipe) joints, the condensing shows up in the form of a yellow dried substance, running out of the joints. And the pipe fails quickly.
  • would?

    systematically on a regular schedule brushing the inner vent of the WH help?
  • icesailor
    icesailor Member Posts: 7,265
    Cleaning Oil Fired WH's:

    It is suggested that they be cleaned annually. I once tried to clean one. I couldn't get the top back on without more work than it was worth and the end result was unsatisfactory.

    There may be someone, but I know of no one that cleans them like a boiler. They are too difficult. I set them as clean as I can and they run fine. Access is usually impossible. I thoroughly clean and adjust the burner. That's the best I can do.
  • Interceptor
    Interceptor Member Posts: 46

    The center flue models are fairly simple to clean, the only disassembly is removing the flue pipe and gun. On most brands you can pull the heat exchanger/baffle out the top which leaves a 6" tube down the center to brush out. Bock is the exception, the "turbulator" fins are welded in.  The bottom of the tank gets scraped/brushed through the gun port than vacuumed out. 
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