What unit to use with panel rads and sidearm

Drewgrizz

I am trying to setup a cheap backup for my wood boiler. The plan is to use panel radiators and a sidearm heat exchanger on a electric water heater. So can I use a condensing tankless water heater to save money or should I go straight to a condensing boiler? Remember this is a backup and I want to keep it cheap, but it needs to be able to heat the home for inspection and be able to kick on if the fire goes out in the wood boiler. It also must be wall hung and small to fit in the pantry with the washer/dryer n water heater. I was looking at the navien condensing water heaters cause PVC is a cheap vent?

SWEI

Before you backup

get the system design right.  http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_10_us.pdf will help.

Drewgrizz

Boiler

I have the wood boiler stuff down, but I have to have a backup/primary heat source for the inspection when I'm done doing the reno.  So my question is can I use a cheap tankless hotwater heater in my primary cirucit as a boiler?  The units say they are condensing which as I understand would mean they have to have fluid returning to them, so I would also say they are considering them as space heating sources?  My gassifier wood boiler will be my primary source for heat and hot water and I will just shut the valves off at the boiler/water heater.  I might fire it up in the summer and shut the valves off to my panels and other circuits if it ends up being cheaper then running the 240v water heater.  I plan on using Myson panel radiators with TRV valves and a Grundfos Alpha pump for my heating circuit, I will also have a circuit running to a sidearm heat exchanger hangin off the side of my water heater, a circuit to my hot tub, a circuit to a water to air heat exchanger in my guest shack, and a extra circuit for future radiant floor heat.  I am planning on having about 1000 gallons of hot water storage so i only have to burn once a day in the coldest weather.

SWEI

System design

Do you have a drawing you can share?  Optimal boiler selection depends on system layout, piping, and temps.

Ironman

Issues

You don't want to use steel panel rads with a wood boiler that is open to the atmosphere. They oxygenated water will rust them out in a short time. You could do it if you use a heat exchanger to isolate them from the open boiler circuit.



As far as using a tankless in place of a boiler: it's a very bad idea. An on-demand heater is not designed, controlled or approved for space heating. It will also have no warranty if used that way. There are numerous threads on here that go into more depth as to the reasons why. Search my posts for a recent one.



You repeatedly use the word "cheap" as a qualifier for your design. You get what you pay for and I know of no other field where this is more true than hydronics. You'll soon find that laws of physics out-weigh the laws of economics - every time.

Drewgrizz

Cheap

I want cheap because it probably won't be used and I am gonna have a closed system wood boiler or an open boiler with a heat exchanger in a closed storage tank so no worries there. My main question was can I use a cheap condensing water heater such as the navien which is around 1k to heat some panel rads and dhow? I don't see the diff between these and the combi's except that they don't have the ANSI rating as a boiler and they don't have two circuits in them? Right now I'm either buyin the nr180 or the ch180 and I don't really need the dhw feature so if I use a primary circulator will the nr series work to space heat?

Rich_49

You Might

want to look at the HTP Phoenix with a solar HX . You could use the solar HX to heat the tank ( hold out burner) , store in the tank at 160* , you could store higher with the commercial unit . Set your wood buffer to pump when either DHW or space heating call . The Phoenix will act as the middleman , a middleman that when your primary source does not deliver will gladly manufacture and deliver what you need  .  The Phoenix has 2 standard outlets on the side which are expressly for hydronic heating of varying types   NOT CHEAP , but nothing that you want to do can be done CHEAP and be of any quality .  http://www.htproducts.com/phoenixwaterheater.html . It is  a water heater , mod con , buffer tank , call it what you will it is versatile and will do what you want . You will need to supply on HX between the Tank  (Phoenix) and rads .  If you just have to go with your initial thought use the Bosch Greenstar boiler . Old reliable HX and good technology , I trust German manufacturing a bit more  than Korean .  Plus the guys at Bosch understand what we do much better than the Navien Tech guys 

Drewgrizz

expensive

That unit is a nice, but pretty much cost more then my whole heating system.  I just want a cheap backup for my wood boiler that is all and I guess nobody has any experience using a tankless water heater as a source for space heating?  That is really all I need to know, I guess I should just ask the local inspector if it is ok and that will answer my question.

Unknown

what make

What make you think the inspector will know more than most of us here?? Cheap is a dirty word here and that's why most people come here after the fact..

Rich_49

Keep hearing

how expensive HTP is . Don't quite understand why I keep hearing that , I am in the largest most expensive market there is and I find quite economical .  Oh well , have at it my friend

Drewgrizz

htp

The price isn't too bad I was lookin at the wrong model, the 9000 dollar one. The inspector will know if I can use a tankless for space heating or not and that will make my mind for me. If I need a ansi rated boiler or not?