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Author Topic: OWB, radiant heat in floor heat... can i add a tankless boiler to the system???  (Read 4585 times)

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Offline brownloggin

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i'm a tree guy not a HVAC scientist...  i'm building my first home this spring for my family.  I've already purchased a slightly used Central Boiler 5036.  we will be doing in floor heat through out the 3100 square foot house of heat able space (basement too).  what i'd like to add is a way to heat the water in case i'm not around to add wood.  on demand hot water.  do the flow rates need to match up?  i'm new to this, and am reading a ton.  also... is a thermal storage tank a good way to store heat energy for my floor system?  thanks for any input. 

Offline doctorb

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If you have a finished, partitioned basement, then the radiant floor heat will be nice.  If the basement will be open storage with standard basement stuff, then the pipes and the heat exchanger to your oil backup furnace gives off plenty of heat to warm a basement.  So, without knowing exactly what you are going to do with the basement (living space, etc.), you may want to save yourself the trouble of putting in radiant down there as the energy that comes in from the OWB is exposed to the air of the basement and throws off plenty of heat.  It's enough that, on cold days, I open the door leading down to my unheated basement from the first floor to let the rising heated air come out.  I realize this may not pertain to your individual situation, but it may.

By the way, I know I failed to answer your specific question.  that's because I don't know the answer.  Wait about 10 minutes, you'll get one!  Welcome to the Forum!
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

Offline Holmes

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 A thermal storage tank will give you more heat storage , that will help.  You could use a tankless boiler to heat the thermal storage tank when the water cools down to maybe 110 to 120 degrees.  The storage tank would be like having the boiler inside, so take all of the heating system piping from the storage tank.
 I am confused, do you want an on demand water heater to make domestic hot water OR a boiler to heat the storage tank , when the wood fire is out? or both?
  Welcome to the FF
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Offline dave_dj1

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Unless your paying for the house out of pocket a bank will make you have a primary heat source, wood doesn't count, at least in these parts.
I would think the best way to have back up is to have redundant systems. The OWB is an open system and an indoor heating system is a closed system. I think you would be ahead of the game to use a plate heat exchanger. I'm no expert though.
The only thing I don't understand with in floor radiant heat is why anyone would want to take the time and energy to heat water to 160-170 just to cool it back down via a mixing valve to 100 ish for the radiant heat.

Offline WmFritz

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Brownloggin, think of thermal storage like a battery. When your boiler is burning, your charging and maintaining the charge of the battery. The length of time the battery will provide heat depend on factors like; size of the tank, heat loss of your home, temperature the tank is heated to... etc. Radiant systems really shine with storage because they can use water temps down to 100 ish.

Dave, your not wasting energy when you mix water temps back down to 100 from the boiler. The mixing valve recirculates the return side and introduces boiler supply side back into the loops to keep the water at the desired temp. This extends the burn time in boiler and keeps the radiant heat at a consistent temperature.
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Offline DeerMeadowFarm

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If I count my basement I heat about the same square footage via radiant heat. I have a E2400 and an oil burner. I run my OWB water through a heat exchanger. In the summer I use the oil for my domestic hot water. My boiler gets filled once per day; at the fall and end of the season I can get 2 days out of a fill. My wife keeps the house warm too; 72 degrees! I'm not sure where you'd need to store more water than your water tank; you're boiler would either be going out or you'd be "forcing" it to burn more often just to keep the coals going.

Offline brownloggin

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1300 square foot (footprint).  basement is a walk out and will be heated.  then the first floor will have tubes stapled throughout the floor joists, then the half story (lofted) will have the same.  i'd like to heat with the outdoor wood burner for my main heat source (closed system).  which will heat a manifold that heats my potable water.  i'd like to be able to heat the water another way (backup).   

the idea with storage tanks if i'm not mistaken is the larger the tank the more energy you are storing and the less burns you need to fire to heat it up?  the initial burn would be high but wouldn't be needed as often????

Offline dave_dj1

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I just re-read your post. I know of a guy that heated his shop with a gas hot water heater. He worked on lawnmowers and such. I would think you could use something similar, I don't know the capacity of a tankless gas water heater is but you should be able to find that info.

Offline bandmiller2

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Brownie, radiant floor heat is dandy but if the water is too hot their not. I have some radiant floor and some baseboard. You can use the baseboard to lower the water temp before it enters the radiant. Baseboard is a good way to heat the basement and could be plumbed as a heat dump. If your going radiant floor don't use tar paper under your finish floor. As mentioned I would put in a conventional heating system and get rid of the inspection varmints then add what you want, but do it right. Frank C.
A man armed with common sense is packing a big piece

Offline limbwood

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If you are wanting AC you will have to put air handler in to do this, it only cost a few hundred more to have a full furnace instead, it would be cheaper to put heat exchanger in furnace than running all that pipe, unless you really want in-floor heating, in-floor isnt the best under carpet but they do make a pad that is better than most. good luck with build.

Offline brownloggin

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mini split heat pump for a/c and backup.  anyone have a one of these?

Offline pabst79

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A heat pump in sub zero temps may not keep up, they work better in a milder climate. Although I know some contractors in our state sell a few of them. When its 33 below, I'm not so sure. You said backup? If your just keeping the inspector happy, the split system would be economical. If your going with a closed system and only going to have 1 or 2 zones, you will probably want some type of backup/dump zone. I have a small fan coil unit that kicks on in my shop no matter what if the water temp reaches 200, that way your not dumping out your relief valve and causing a mess. 
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Offline DDDfarmer

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I'm building this summer as well.  I  have learned never to mention "wood burner/boiler" to anyone related to insurance or bank.  So wanting to have a back-up system as well I'm looking at a high efficiency propane hot water heater.  Should get me the approval to meet Ontario's sb-12 guidelines and thumbs up from the insurance.   

My cousins house I'm told is heated with a on-demand natural gas heater. I havn't seen it but he has said that he likes it.
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Offline WmFritz

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http://www.supplyhouse.com/Takagi-T-KJR2-IN-LP-T-KJr2-IN-Takagi-Tankless-Indoor-Water-Heater-Propane


I bought this on-demand heater for our radiant floor heat at the cabin.

2350 sq ft of living space with a 15' ceiling throughout the second floor. I have 1200 lineal ft in the first floor slab. 380' buried in the outside wall in the family room and 1000' of staple-up for the second floor. This heater is rated at 140,000 btu's.

We're in our 5th winter right now and I like this heater alot.  One thing to note though. I designed my own system (which turned out to be way tougher then I thought). My unit requires .8 gpm of water flow or the gas valve will not open. I think I redesigned the primary loop 2 more times before I could keep the flow consistently above 2.5 to 3.2 gpm through the heater.

My plan is to tie in a wood burning boiler to my system. I hope to do that later this year. I also have the same size heater for the domestic hot water. Last year, I installed a larger BTU unit at our home.
~Bill

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Offline brownloggin

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ahh, someone with the same idea.  good.  now i just need to design my own with my outdoor wood burn mixed into it. 

Online Southside

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I sort of did what you are talking about, sort of.  I plumbed a circulator pump into a plate exchanger with its own thermocouple to control it through the electric water heater, coming off the top and back into the bottom flush out. The other side of the plate was plumbed into a zone coming off the boiler. This allowed me to heat the water in the potable tank using the boiler heat, when the boiler was not running the elements in the water tank would heat the water - so in my case the tank elements became the backup for the potable water.   I see no reason why a tankless heater would not work just the same, using a plate exchanger you could keep the waters from ever mixing if that worked in what you are building.  It was not complicated at all, but seems to be when trying to explain it here. 
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Offline brownloggin

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Can i just run my OWB system... and have a tankless water heater tied into it... maybe have it heat a thermal storage tank...

Online Southside

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That would be exactly the same principle as what I had except your storage tank was my water tank.  If you ran a circuit off the tankless heater through the storage tank that was independent of the OWB then you would be able to heat the storage tank only and not have to heat the entire OWB as well.  It could either be done with a plate exchanger or directly depending on how hard your water is. 
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Offline mapleveneer

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Just my two cents worth, maybe it isn't even worth that much.  My house was built in 1940.  In 2012 we did a major basement renovation.  We removed the old furnace and gutted most everything.  I mean everything, took out the concrete floor, walls, ceilings, everything that didn't support the first floor.  Installed radiant floor heat in the first floor (cellar ceiling) and in the new concrete basement slab.  Installed a wood boiler in the garage feeding the house through about 100 ft. of underground insulated pipe.

The feedback that I would give you:

1. Put the radiant in your basement floor regardless of what your plans for finishing the basement are.  This is the only opportunity that you will have to do that.  My wife now works in her basement sewing room barefoot when it is  zero outside.

2. Radiant in a concrete floor will work with 100 F water temps.  Your wood floors are really insulators making it much harder to force the heat through to the first floor.  You will probably want 160-180 water temps in the first floor zone.  On the cold nights, I run mine around 170 or even a little more.

3. Radiant under a wood floor is very slow to react.  It can take hours to raise the room temperature a degree or two.  Carpets and rugs have a significant effect.  The warmest place in the house is under the couch where the dust ruffle traps the heat in.  Stick your feet in there if they are cold.  It makes sitting on the couch quite pleasant also.


Online red

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