Long time reader new poster
Hey all,
I'm a retired General Contractor and building a new home here in Montana and was hoping to seek out a little advice on this Radiant system I've designed. Over the years I've seen lots of radiant systems but have never really installed one so was hoping for input. I've attached a PDF of the plumb out and had a question regarding how I have it plumbed.
I designed this with the thought of redundancy eg: If one of the tankless heaters decide to go south for the winter I can isolate it and the other will continue on with luck. Also I have a lot of heating (3500 sq. ft.) or so with a potable hot water recirc line. I was hoping one of you smart fellers could look this over and see if I thought of everything including proper parts and pieces that might have been overlooked or left out.
I appreciate your time and your opinions feel free to critisize, ostersize, or otherwise slap my design around as you see fit!
Comments
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- I wouldn't use an on-demand water heater as your radiant heat source for many reasons as you can see if you do a search on this website. Use a boiler like Lochinvar, Viessmann, IBC….
- You have an open system (DHW and hydronic water) and you cannot mix the two. Depending on your hot water needs, you have a lot of choices: on-demand for DHW and boiler for hydronic or combi or boiler with an indirect tank.
- It's recommended to install a primary-secondary system for your piping, again, for many reasons.
- What is the bypass for around your recirc. pump?
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
3500 sq ft, probably a heating load under 80,000 btu/hr. You need a load calc to know.
How many square feet of snowmelt? Figure at least 100 btu/ sq ft.
I would seperate the snowmelt from the home heating. I'll bet the snowmelt is a much larger load. If you want simple a copper tube boiler works well for SIM. No need to have modulation (mod con) in a one zone system.
If you chose to use two boilers (not water heaters) I would put them together like this. One would be a 100,000 which probably covers the house load. The second large for when the SIM run
Then add an indirect for DHW
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
The snow melt system does not have an expansion tank. Hot Rod's sketch above does and you need one.
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Your original design is NOT good. Pay attention to the information coming to you on this forum. Starting with the principal heat source….use proper boiler(s) NOT domestic water heaters. Those are the wrong machine for the job.
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I would completely separate DHW and heating systems. CLosed heating system, low pressure, with oxygen barrier piping.
What is your design heat load?
I'd go with Modulating condensing Boiler on your heating system with appropriate piping. Tankless vs HP vs indirect for your DHW. Can your home design support a vertical drain water heat recovery for your most utilized shower(s).
Will you have generator back up? If not, you may want a DHW tank instead of NG tankless.
- as @JDHW pointed out, expansion tank/air separator/pressure relief on snow melt/glycol loop.
- You only need one circulator supplying the radiant manifold. whats the reason for the redundancy?
- Ideally your air separator should capture 100% of flow, the way you have it drawn, its not capturing flow through the heat exchanger.
- Make sure to have stainless steel circulator on the DHW side.
- For the DHW circulator, I put that on the return line, with isolation valves and check valve. On the return line, it will not be restricting DHW flow to fixtures, the pump will see less flow overall (less wear? not every shower will be going through circ), and it will operate at a lower temperature.
- In general the circulators clear air easier when they are located as low as possible as system design permits, and when oriented pumping up, but these criteria are not mandatory or always possible.
I look forward to seeing your your updated design
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Thanks Alan for your reply, and yes I have been doing a lot of research on both tankless heaters and boilers I had a house that had tankless Takagi heaters for the radiant system and they worked flawless in the 5 years we lived there. Their efficiency was incredible and never had a problem. Although I'm not against taking advice on this matter I do know there is tons of real world applications out there utilizing tankless heaters as long as they are built for the application.
With that being said the Noritz 111 is actually built for both DHW and Radiant according to the Noritz reps. I have talked with Radiantec on the matter and they also recommend the Noritz for this application.
The bypass around the recirc pump is for the tankless system, if you don't have that loop when you open a faucet the Noritz would not energize because the recirc valve isolates the loop.
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Hey HotRod thanks for the comment,
What is the Hyd Separator? Is this just a loop for redundancy? The snowmelt is around 400 sq. ft. I'm going to put in a smart enabled power outlet for the snow melt so I can run it whenever I need it otherwise it will be sitting idle. I do have it on a separate loop from the rest of the system. Each Noritz is rated at 199k btu so there should be enough there according to the numbers I believe. If you were to recommend a boiler what would you suggest? I would like something that mounts on the wall with space consideration. I have been looking at a Weil Mclean 150H as an option
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Howdy bjohnhy, Thanks for getting back with me on this.
Yes I am installing a backup gen-set there is nothing worse here in Montana than a 6 hour power out when it's subzero.
The Gundfos Circ pumps are supposed to be some of the best pumps available Alpha series ECM that have built in air separators already, they also are capable of sensing pressure needs for the system, not sure just what I have been seeing on these pumps.
There is 2 circulators simply due to flow, each pump can handle around 12 gpm and I was getting close to maxing out one so threw in two.
The bypass on the recirc line is what will be handling the demand flow when a shower is running the pump will not be in the system during shower ops, it's just going to be keeping hot water in the loop so it doesn't take half a day to get the water warm.
I will work on changes for isolating the DHW though it makes more sense of course, I haven't used these plate exchangers at all or ever been around them, do they work pretty efficiently or is there a noticeable difference in heat loss through them?
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The are just estimates based on an efficient new build.
3500 sq ft X 25 btu/sq ft would be 87,500, for the house. Although we see new homes in cold climates with loads in the teens so 87k could be on the high side
Do the heat load calc it is important.
Would you build a house without a blueprint and joist sizing, etc?
400 sq ft of snowmelt at a good btu rate
400X 125 btu/ ft is 50,000 btu/ hr
Combined on one boiler a single 150,000 boiler would do the job
Or a 75,000 boiler for SIM, 100,000 or less for the home.
In the mountains of Montana, or Havre😏?Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
”Alpha series ECM that have built in air separators”
Never seen this configuration before, can you provide link?
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many of the new ECMs have a pump venting function. Best I can tell is it just runs it a a higher rpm for a period of time.
It can help purge the circuit a bit also. But obviously you need an air separator to remove the air it attempts to shove around
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
These circs do not have air separators in terms of removing air from the system. But they do a better job of evacuating air from the circulator itself compared to older models.
Re the DHW recirc line, you won't need a bypass if you put the circ on the return line. Its my understanding that the bypass is potentially useful when there is not a dedicated return line and a crossover valve is used at furthest faucet.
A heat exchanger between the tankless and radiant loops would be less efficient. How much, its hard to say. But your return water temp entering the tankless will end up being 5 to 20 degrees higher than if piped directly. One of the issues with using two tankless in parallel as you have drawn, is the minimum flow to activate the tankless is effectively doubled.
The house i live in now has a tankless supplying the radiant floor. It was there when i moved in. DHW tankless goes to heat exchanger, which supplies the closed loop floor. It works, keeps house warm. But I would not build a new house with this sub-optimal design.
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Please stop talking to Radiantec immediately!
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I'm sure there are good designers at RT it's just unfortunate that we see the the worst of the the designs and installations not the ones that work. I've seen both.
Miss Hall's School service mechanic, greenhouse manager, teacher, dog walker and designated driver
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You seem to be unjustly overconfident in your design and information. Radiantec is a disaster and I think just about everybody knowledgeable in the trade would recommend that you forget everything they told you. There is no such thing as a circ with a built in air separator either. You're obviously welcome to do as you please, but the correct way to do this would be to scrap everything you've got so far and start fresh with a new design using the proper equipment.
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Actually there is such a thing as a pump/ auto purger.
This one invented by none other than our friend John Ruhnke
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream2 -
"One of the issues with using two tankless in parallel as you have drawn, is the minimum flow to activate the tankless is effectively doubled."
That, I never though of. Thanks, @bjohnhy
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab1 -
Is this system on any typical circulators used for hydronics?
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When God created Montana he gave Havre to the devil. I went to college in Havre and have been stuck there for long periods of time with the Railroad and have to say I have never been someplace that could be THAT cold! I live in Columbia Falls Gateway to Glacier Park, still gets cold but nothing like Havre / Great Falls.
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We are talking about two different things here. The alpha 58 does not have a port to vent out air. It modulates the motor to send the air on its way through the pipe, so it can be removed by the dedicated air separator in the system. Did you watch the video the link goes to?
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I lived in a cabin in Whitefish no running water, a wood stove and outhouse plumbed a fee of those lodges at Big Mountain
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
You were a homey! Although Whitefish is more snobville these days, can't afford to live there anymore median price on houses over there is at $800k these days.
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I was there in the 80’s You were either a “rail” worked for the B&N, worked in the lumber industry, or a hippy. But everyone got along and gathered at the Great Northern, Stump town, Caseys, etc
When times were good everyone was in the bars, when times were bad everyone was in the bars
Our place was on Haskell Basin Rd between CF and the fish. That is probably prime real estate now.
Great country, great area to see the northern lights.Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0
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