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Radient heat source

jp_2
jp_2 Member Posts: 1,935
in THE MAIN WALL
in a sense they need to be tougher than a boiler.

full bore starts and stops, designed to take in 50F water, constant short cycling.... Iam starting to think differently.

No standby losses.

Comments

  • John Callaghan
    John Callaghan Member Posts: 1
    Raidient heat source

    I have run some radiant tubing in an extension on my house and i was wondering if I could use a tankless water heater to heat the water instead of a regular water heater? I only need 20,000BTU output!
  • Unknown
    Unknown


    regular water heater will likely be a better choice.

    depending on where you are though, you might want better efficiency. You're not that far out of a real heating load, if you have a lot of degree days you might consider something higher efficiency like a mod/con, even with a buffer tank.

    All depends...
  • ALH_4
    ALH_4 Member Posts: 1,790
    Water Heater

    I agree with Rob. A tank-type water heater is probably the best, least expensive, and simplest way to go. I am not a big fan of using instantaneous water heaters as a heating source.
  • Unknown
    Unknown


    taking in 50 degree water means not short cycling. 60 to 70 degree temperature rise. At one GPM that is 1 gallon x 60minutes x 8.4 lbs/gallon x 60 degrees = 30,240 BTUs/hr.

    Hardly a 'short cycle" situation.

    They need to be more resistant than a boiler to corrosion, and they need to dump a lot more heat into the water in "one pass". Neither of those things are important to heating and in fact that "fast dump" is a detriment to some degree.
  • jp_2
    jp_2 Member Posts: 1,935
    takagi tk3

    modulates down to 11,000btu's. what other boiler can do that? and something like .5 gpm to start?

    short cycling is briefly washing KFC chicken grease off your fingers... :) or multiple kids in house.
  • Unknown
    Unknown


    are you kidding? KFC chicken grease takes forever to get cleaned off ;)

    11kBTUs, great, that's still more than half of this guy's load, assuming that no one is being conservative.

    A boiler can't handle that either, but that's why a buffer tank was mentioned. If he has enough degree days that efficiency is a major concern, mod/con and buffer tank is the answer. If not, a tank heater is likely the best answer. Note that both of those solutions have buffer capacity.
  • ALH_4
    ALH_4 Member Posts: 1,790
    Boiler, Instantaneous, or DHW Tank?

    It raises the question, why aren't boilers designed like instantaneous water heaters or vice versa?

    Instantaneous water heaters are designed to provide low flow, high delta-T operation. Relatively small heat exchanger passages help provide additional heat transfer, but increase the head loss. Some are not designed to accept warm return water.

    Boilers are designed for a relatively low delta-T with higher flow. Passageways are more open to keep head loss low and provide adequate area for the flow rates necessary. Pumping requirements are less and therefore electrical consumption is reduced.

    Can instantaneous water heaters be used as boilers? Obviously yes, and sometimes with good results. Is there a ROI for using an instantaneous water heater instead of a tank-type in low load situations like this? Probably not. Plus there is very little to fail in a tank-type water heater. When dealing with small systems like this, a service call will affect ROI a lot.

    At least that's how I see things. I know lots of people are using these units as boilers and they say they work fine.
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