New Radiant Heat System Questions

flyingmeatball

Hello,

I'm reaching the end of the design of a new radiant heat system and I was hoping to get some feedback and ask a few (probably dumb) questions!

The project is a gut reno/addition - we bought a ~2400 sq ft house built in 1953 and basically removed everything but the foundation/unfinished basement. We are adding a second floor and expanding a couple rooms. It is now 3,500 sq ft with a second story. I have attached simple floorplans.

So far, here's what I have for radiant heat design:
--Total heat loss of the home is 105k BTUh.
--Looking at open system design.
--The plan is to do a thin-slab pour on the first floor - the current flooring has been taken down to the concrete panels (they didn't use wood - very sturdy). The second floor will be run between the joists with metal heat fins.
--I'm looking at four zones, two on the first floor, two on the top floor. The zones will be:
Zone 1: 780 sq ft (630 with piping - no pipes under showers, in closets, etc). Heat Loss of 17K. Consists of Master br, master closet, master bath, 1st floor guest bath and bed.
Zone 2: 1,145 sq ft (857 with piping). Heat loss of 40K. Consists of living room, dining room, kitchen, entryway, sun room, mud room.
Zone 3: 800 sq ft (750 with piping). Heat loss of 18K. Consists of den, office, laundry room.
Zone 4: 750 sq ft (700 with piping). Heat loss of 12k. Consists of two upstairs bedrooms, 2 bathrooms, and loft.

Equipment I'm looking at so far:
Takagi TH3DV-NG on demand water heater
Everhart 1/2" oxygen barrier PEX tubing
Rifeng stainless steel manifolds
Grunfos stainless steel variable speed pumps

Questions:
--My circuits can only be 300 sq ft, where does that measurement start and end? From manifold back to manifold, or from water heater and back?
--My water heater and zone pumps are going to be located in the basement. That's pretty far from the top zones. Should I move the manifold for the circuits upstairs? If I do that, how does it impact my 300 ft circuit length? Do I need to add the copper distance from the pump to the manifold to the circuit? What's best practice between moving manifolds and "homerunning" as I've heard it called?
--In my master bedroom zone, the master bedroom itself is looking like it will require more flux than I think should be planned to output. It will take 41.77 btuH/sq ft, but the other parts of the zone (hallway, master closet, master bath, second bedroom) will require much less than they are suppled. To what extent should I assume that the heat will move from adjacent areas separated by interior walls? The bedroom itself has a crawlspace below it, no structure above it, 9ft ceilings, and a 16ft wide window wall. Should I just keep the same 10" tube spacing throughout the zone and maybe adjust the flow rate up slightly in the circuits going through the master bedroom and down for the other circuits, and then plan on having to use a secondary heat source in there, or can I safely micromanage the flooring to get it warm enough without having the flooring get too hot or the flow rate too fast?
--How should I account for heat loss from the unfinished basement, which I wasn't planning on heating? That area is included as a source of heat loss, but there is nothing in that area to offset - should I just apply that heat loss to the rooms directly above it?

Thanks so much for any assistance or insights!

JohnNY

flyingmeatball said:

Questions:
--My circuits can only be 300 sq ft, where does that measurement start and end? From manifold back to manifold, or from water heater and back?
Manifold to manifold. Read the numbers stamped on the tubing as a guide.

--My water heater and zone pumps are going to be located in the basement. That's pretty far from the top zones. Should I move the manifold for the circuits upstairs? If I do that, how does it impact my 300 ft circuit length?
If you can stay within your 300' tolerance, it's my preference that all the mechanicals stay in one place: the boiler room. If it helps with your loop lengths, which is often the case, move the pump and manifold closer to the areas they serve.

Do I need to add the copper distance from the pump to the manifold to the circuit?
No.
What's best practice between moving manifolds and "homerunning" as I've heard it called?
Copper. Large diameter PEX. Your call.



--In my master bedroom zone, the master bedroom itself is looking like it will require more flux than I think should be planned to output. It will take 41.77 btuH/sq ft, but the other parts of the zone (hallway, master closet, master bath, second bedroom) will require much less than they are suppled. To what extent should I assume that the heat will move from adjacent areas separated by interior walls?
The heat will not move to warm the undersupplied areas. You'll need supplemental heat in the Master Bedroom.


The bedroom itself has a crawlspace below it, no structure above it, 9ft ceilings, and a 16ft wide window wall. Should I just keep the same 10" tube spacing throughout the zone and maybe adjust the flow rate up slightly in the circuits going through the master bedroom and down for the other circuits, and then plan on having to use a secondary heat source in there, or can I safely micromanage the flooring to get it warm enough without having the flooring get too hot or the flow rate too fast?
--How should I account for heat loss from the unfinished basement, which I wasn't planning on heating? That area is included as a source of heat loss, but there is nothing in that area to offset - should I just apply that heat loss to the rooms directly above it?
This is a tricky thing. I'd call the MB floor a cold partition and plan for something like the worst.

Thanks so much for any assistance or insights!

flyingmeatball

Thanks @JohnNY - two quick follow-up questions:

1) If I move the manifold, do I have to move the pump with it or can I leave the pump in the boiler room?
2) the "cold partition" for the basement runs under the entire first floor of the house, not just the MB. Is it best to adjust the manual J for every 1st floor room to account for that?

Mark Eatherton

As a survivor of Legionairres Disease, I'd strongly recommend that you re-consider the open system. There is NO safe way to keep from exposing your family, and yourself to this deadly disease.

Seriously.

Plus, the warranty on equipment that is not being properly deployed (Takagi) is less when used for space heating applications. I guarantee you I can (and will) deconstruct any counter arguments you can come up with. Do it with a boiler, and an indirect water heater, and if you are short for space, use a plate heat exchanger for DHW production. You won't regret it. If you go open loop, you will regret it.

ME

Zman

I think you should stop visiting whatever web site told you to use a tankless water heater and an open system.
You should be using a boiler and a closed system, period.
Be very careful of concrete topping in an old house. Depending on the kind and type of concrete, you could easily be adding 10,000 to 20,000 lbs to the floor.
I would suggest finding someone to help you design this.

flyingmeatball

@Zman @Mark Eatherton thanks for the insights. I liked the open direct system because it was efficient to operate both radiant heat and DHW with a single high quality water heater. Is there a good way to do that without jumping all the way to the expense of a boiler?

The radiant floors on the main level were planned for by the architect/structural engineer, so concrete weight shouldn't be an issue.

Gordy

If you are insistent on that method, then a FPHX (double walled) is a must for the radiant side. This will not only protect the domestic side from bacteria, but will also allow the use of ferrous components on the radiant side. Provided of course you use O2 barrier pex.

However the system efficiency will not be there.

Mark Eatherton

It's painfully apparent that you want the efficiency and comfort of hydronics, but don't want to have to pay the price. Honestly, tankless heaters are CHEAP, in more ways than just initial cost. During the lifetime of this system, NOT including doctors office visits due to bacterial pneumonia, you will pay more to operate this system than you would a conventional hydronic boiler with the ability to do DHW as well.

The "promoters" of these cheap systems like to ignore the fact that they are known for amplifying Legionella. During the summer months, you will have water sitting out on the radiant floor in perfect "petrie dish" conditions, allowing the bacteria to multiply.

If you happen to be so unlucky as to be in the shower, and have even so much as a simple cold, and the pump for the space heating system turns on, you will be showering in bacteria which when inhaled, will cause you to contract the disease known as Legionairres Disease, or its weaker cousin Pontiac fever. Having a timer on a pump (IPC requirement) to ensure "fresh water" doesn't work. It only guarantees the bacteria will get the oxygen, and food it needs to continue flourishing.

I contracted LD, and I wouldn't wish the disease on my worst enemy. Check with the Center for Disease Control and see what they have to say about Legionaires Disease. It's omni present in the dirt, therefore its in the water. The only method for eliminating it is scald sanitization, which means keeping the system as a whole at a temperature above 130 degrees F, preferably 140, then mix it down to 120 degrees to the end use points to avoid scalding conditions at the point of use. Not feasible on a tankless RFH system.

Chlorine would have to be 10 times stronger than is typically allowed to kill the deadly bacteria, and then all of your plumbing would fail due to the elevated chlorine concentrations, if you have chlorine.

Seriously, look into ANY "combo" hydronic system, and you will be very glad you did. If you're REALLY handy, and want to "DIY", then hire a professional system designer to give you guidance on your project. It's not rocket science... It's harder than rocket science to get it right.

In reality, the tankless heater was made for a constant flow, with a specific temperature rise of 100 degrees F, like you'd expect with a shower. Radiant is a tight differential, like 10 to 20 degrees F, with highly variable flow rates and the heater will short cycle. The WORST thing you can do to ANY piece of equipment, is to short cycle it.

Don't become a victim of the internet radiant heating system salesman. They will be no where to be found on December 25th, when you have no heat and no hot water, and IF you happen to be fortunate enough to get in contact with them, they will tell you that it's apparently YOUR fault...

Don't be a victim. You can do it right the first time, or do it again, and again and again. Trust us. We see it all the time.

Got questions? We do.

Have you done a heat loss calculation yet?

Have you calculated your DHW needs?

Got a large volume tub to be filled?

ME

DZoro

Very good advise has been given

flyingmeatball

@Mark Eatherton Thanks for the insights - I'm not set on any one system - just trying to do my due diligence. I'm not looking to cut any corners, but I am looking to do the majority of the install myself - which has made it hard to find an affordable designer/engineer - all of the radiant people I've reached out to in the area also want to do the work.

I have a detailed heat loss calculation done by a reputable company, which I have double checked with a second version I did on my own, zone/room requirements, and a rudimentary parts list. I also have my house fully entered into loopCAD, apart from the circuit layouts.

DHW use isn't that much - just my wife and I and we're more shower than bath people.

JUGHNE

I realize it is hard to think of now, but you should consider the resale ability of what you are now building.
Years down the road it is possible that Legionaries and other issues are at the top of the home inspectors list.
If you have a traditional boiler with indirect tank then not only you have eliminated the bad water issue but most hydronic people could work on it. Also you would have DHW supply to satisfy the standard needs of most future owner. IMO as an "old guy".

Gordy

Here’s what happens to an open system in the summer. You isolate your heating system, then that water lays stagnant in the tubing breeding bacteria until heating season. Then you open up the heating side, and all that stagnant bacterial saturated water hits the tank. Then you wash, and bath with it for a while. With a closed system it stays where it should, in the heating system.

You can isolate that with a FPHX. However I think you need to look at the two systems, and compare costs. Is it worth the money saved for the extra maintenance, and risk of an open system? Is it worth passing it on to new owners in a sale?

Radiant heat is a premium heating system when done right you can’t get around it’s cost. You can try, but you will be disappointed.

the_donut

Lawsuits are more expensive than upfront costs if you sell. My 2¢.

Rich_49

Thanks so much for any assistance or insights!

flyingmeatball said:

@Mark Eatherton Thanks for the insights - I'm not set on any one system - just trying to do my due diligence. I'm not looking to cut any corners, but I am looking to do the majority of the install myself - which has made it hard to find an affordable designer/engineer - all of the radiant people I've reached out to in the area also want to do the work.

I have a detailed heat loss calculation done by a reputable company, which I have double checked with a second version I did on my own, zone/room requirements, and a rudimentary parts list. I also have my house fully entered into loopCAD, apart from the circuit layouts.

DHW use isn't that much - just my wife and I and we're more shower than bath people.

You should use my phone number to discuss . I have designs installed by others including homeowners / DIYers throughout North America . Maybe I can help or many others here who are comfortable with such situations

flyingmeatball

Point taken by all - will go with a closed system. Thanks for the insights.