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Tankless forced air heat - missing link

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Steve_133
Steve_133 Member Posts: 7
in THE MAIN WALL
What you say is absolutely true, but one question I have is that if it was a short distance closed loop system wouldn't the water always be hot and the tankless heater, in conjunction with a circulator, keeps it at a temperature. The idea is to put the TH next to the coil itself and not lose heat from travel. So it would be between 120 and 140 degrees continuiously. The blower would only come on when you want hot air circulated (based on room temperature) - it would have little to nothing to do with turning on the tankless heater. The pump would keep the right volume going through the coil and as needed the heater would kick in to heat it back up again. I am not sold, just like asking a lot of questions - like would I need an expansion tank? would I need two pumps (like you said to better control flow), one a primary and the other a variable speed injection. .. ho hum...

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  • Steve_133
    Steve_133 Member Posts: 7
    Tankless forced air heat - missing link

    Hello, I am trying to activate two hot water coils that were installed with my central AC which is two seperate systems, one 500CFM and the other 600CFM.

    I plan on connecting a tankless hot water system to each coil through a circulating pump. Sizing wise; 4GPM at 120 degrees gets me about 25,000 BTUs from each coil (totalling about 50k for whole house). My heat loss calc says I need 24,800BTU. So, it sounds good, but.. What specifically do I buy for a pump that I can connect to the thermostat? the way I see it, the pump starts based on temp and the flow of water kicks in the tankless unit and shabam! but I have the coil, and tankless units are pretty straight forward, but I need info on the missing link (thermostat connected circulating pump). And if I am crazy in my plans I'd like to know that too.. =)
  • don_182
    don_182 Member Posts: 69
    Yep you're crazy.

    I've never seen a tankless as you say... pretty stright forward.

    For me flow thru these unit are very hard to control even
    with a burner that modulates.Hopefully yours does if not, you will soon find out why.

    Also keep in mind if you do have one that modulates it firing rate how will you control the fan speed on your airhandler? Not a big worry if you are one of those people that have no problem with chill air blowing down the back
    of your neck.

    Oh well...it easy and anyone can do it because it says so
    right on the net!!!!
  • Perry_2
    Perry_2 Member Posts: 380
    So...

    I'm a homeowner like you; and I am wondering what is your existing heating system? Why are you looking to change?

    Theoretically, what you are proposing might work - if done right. However, I've been reading post here for several months and it seems that using a tankless hot water heater often has issues.

    My proposal to you is spend a month or so learning before you tread down the path you are looking at. There are some great books that can be purchased as well.

    If you are patient you can get lots of questions answered and learn a lot about heating here. You are problaby not going to get people who are going to lay out the details on how to construct a system - and all the issues that could come up at one time.

    Perry
  • Steve_133
    Steve_133 Member Posts: 7
    Its not my patience that is the problem..

    Hey Perry,

    I have actually spent a great deal of time bouncing between several HVAC firms, distributors, and contractors. Put simply (in my area) there are very few poeple who know how to handle hydro heat with a Unico High Velocity AC system. That said I expanded my search and this site was a long shot. Even if we remove tankless from the equation and use a small basic hot water heater - thats ok.

    Timing is really my only problem as it is now (after 6 months on this) getting rather cold - my original heating was old steam and it blew up taking floors and few thousand dollars of damage with it - pipes get old, you cannot replace them and you can only get out of the way when high pressure liquid steam goes beserk - so its gone, I sent the radiators and the boiler into space (actually I gave the boiler to a relative). So I need heat - going down this path will cost about $1000 and if it doesnt work I can still use the tankless heater for hot water and do something else. Most of this has been an education in order to bridge the gap between what traditional HVAC people do and what I actually need to do. The principle is almost the same as radiant heat except I only need to heat a coil not a bunch of pex plumbing. There would be two systems and each would hold about 3 gallons of water. I should also point out that it is not the only source of heat I am putting back into the house. The main floor will also have underfloor radiant and baseboard in the basement. So the forced hot airis above that and picking up the slack.
    On the note about tankless problems, I have heard some bad things but mostly related to a brand and not the concept. Rheem appear to get high reviews from what I have seen.

    My average winter heating bill was about $600. Its time to stop paying that.. the steam boiler I replaced was only 6 years old and "supposed" to be efficient. To me efficient is only heating 3 gallons of water in a coil, not trying to pump boiling water throughout a house. If the coil breaks, replace it, heater breaks, replace it - blows up, I can contain most of the problem.

    So, for you as a homeowner, when it all goes horribly wrong, and the HVAC people give you blank looks and your questions are answered with crickets, guess who is really going to be looking after this thing =)

    Appreciate the warnings - I am going to have someone qualified check it over before going live. But containement is the bigger driver for me now.

    Steve..
  • Ted_9
    Ted_9 Member Posts: 1,718
    really?

    isn't it the same price to use a boiler? Why cant you use an appropriate heating device. What about local codes and insurance company?

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Steve_133
    Steve_133 Member Posts: 7
    Interesting point.

    Are you suggesting that a hot water heater is less safe than a boiler?

    I ask because the potable hot water coming out of my tap is between 100 & 110 degrees (and I can turn that up if I wanted to - its on the setting 2 out of 5) and I don't need more than 130 degrees to the hot water coils.

    I will know the details about local codes when I get closer to knowing the specifics and fill out the paperwork - but I am confused as to why a hot water heater is going to be a bigger problem than a pressure/boiler solution.

    Otherwise, the less expensive the job is the lower the permit expense (our town works that way) and they also increase your taxes if you improve your house (your taxes go up in proportion ot the permit cost), so I am going after the tax rebate (energy save initiative) to counter that.

    Insurance? using a simpler, lower temperature solution, meeting code requirements, why would insurance be a problem?

    Insurance and Code are not frightening things to me - what is your point specifically?

  • jp_2
    jp_2 Member Posts: 1,935
    Efficiency

    the tankless I have seen are around 80% efficient.

    people here have claimed over 95% efficiency on mod/con boilers running at your temperatures.

    general type water heaters seem to be more around 70% efficient.

    boilers tend to be more fleixble than standard hot water heaters.

    by the way, my insurance was recently cancelled because "they" felt my electric service was not large enough, even though it was 20% larger than National Electrica Code specified.
  • LarryC
    LarryC Member Posts: 330
    Water Heater Temperature

    Steve,

    Home owner here.

    Do search on the Wall about Legionares disease and bacterial amplification. One of the Professionals here just had a run in with LD. I believe it is recommended that the water heater temperature should be 130-140 F in the tank and use a tempering valve to reduce it to a safe faucet temperature.

    Controls for your heating idea, you would need a thermostat that would turn on the blower fan and start the circulator pump. You will also need an expansion tank, safety relief valve, fill valve with back flow preventor, potable water isolation valve, drain valve, spring ball check valve, circulator style pump, and air removal valve. I do not know if using the heater in a closed system like this, triggers a ASME pressure vessel requirement or not.

    Larry C
  • Steve_133
    Steve_133 Member Posts: 7
    Yuk..


    I never had any intention of mixing potable water with heating systems, but I am going to look into it for my regular potable hot water anyway. Upping the Setting 3 or 4 out of 5 is starting to look better with a valve.
  • Steve_133
    Steve_133 Member Posts: 7
    Heard the same

    That is the same information I am getting too. Plus many of the smaller residential (newer) boilers are all-in-one to an extent, unless you run 2 zones (extra pump etc).

    I got in contact with a manufacturer who is willing to help me spec out the rest and I have help on standby to do the installation.

    I guess the compromise was a smaller efficient boiler to do the specific job and not make it into a whole house activity.

    Thanks for the advice here as well - you were absolutely right.

    P.S - The electric service is the least of my problems in this case as we covered all those requirements when we installed the AC in the first place.
  • LarryC
    LarryC Member Posts: 330
    Mixing potable water

    Steve, I was talking about filling the heating systems. Once the heating systems are full and vented, there should be NO connection to the potable water system.

    Larry
  • Perry_2
    Perry_2 Member Posts: 380
    Hmmm

    Steve:

    I have read your various post here. I do say, I'd have fixed the steam system and kept the radiators - or converted them into a hot water system if they had adequate size.

    As far as efficiency goes.... a mod con boiler is the way to go --> But only if you hook it up correctly. If you have been working on this issue for 6 months - and are where you currently are: Then I suggest that you hire a professional to install a proper heating system (the whole thing).

    Perry
  • Steve_133
    Steve_133 Member Posts: 7
    Yes well..

    The repairs and work on other issues in my really old house has delayed the "actual" work on the new heating, it's one of those situations where to do this means having to do several other things. The several other things are all back in line now and I can move on.

    As it stands now a professional is specing out the whole thing and providing the bill of materials etc. So we are entering the winning stretch.
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