Toester heater waay at the end of the line

Mikey1970

Hello

My 10 year old kitchen tacked onto the back of my 100 year old home is freezing.

The Toester under cabinet fan/coil does not blow all that hot because it is at the end of the line.

The remainder of the house is the original cast iron radiators. 



I was thinking that one way to increase the heat input into the kitchen would be to repipe all the hot water to run through the toester FIRST, then to the rest of the house.  Also, I would run a second toester in the kitchen, piped in parallel to the first one.

My system is a 2 inch gravity system, with a circulator added decades ago. 

I plan on using PEX for the to/from toester connection.  It will be easy to work with and not alot of elbows.

I might be significantly lowering the gallons per minute thru my system, but I am not sure what the affect will be. 

Thoughts?  This looks good on paper. 

Ironman

Path of Least Resistance

What size are the lines running to the toester? Small lines to, or inside, the heater will restrict the flow in proportion to the larger lines in the rest of the system.



I would recommend adding a second circ in the smaller lines to the Toester. You probably won't need a second heater or any repiping.

Brad White

The reason toe-kick heaters

are installed there is so they are easy to kick!



Not really fair to say that, but so often they are mis-applied.



If your gravity HW system is operated by a space thermostat directly, you will find that you have an indirect form of outdoor reset. The firing times are greater in colder weather and fewer in milder weather so by default your water temperature mimics outdoor reset performance. Also if your house is over-radiated (as many are once the enclosure is improved), your house is satisfied more easily and with temperatures so low that they do not trigger the toe-kick heater aquastat.



There is also an issue of Hydonics 101 here: A toe-kick heater is the same thermally as fin-tube. Low mass, quick to heat, quick to cool. If coupled to a cast iron dominated zone, the toe-kick heated space loses out, cools off and delivers no heat to speak of while the rest of the house is satisfied.



As Ironman said, making that its own zone makes sense, direct off the boiler I would add. You can complicate things by forcing the boiler to be hotter and this will overheat the cast iron zone. (Tail Wags Dog), so you would decouple the cast iron zone onto a dedicated control valve to shield it from higher temperatures it does not need. The downside is, your one heater will govern your boiler operating temperature.  No way to make that space back into cast iron heat?

Mikey1970

Still think it is worth a shot.

The lines running the toester are 1/2 inch copper, but they are at the end of a 2 inch iron pipe.

Yes, I am running by the indirect form of outdoor reset Brad describes. The toester fan never turned on, so I bypassed the toester sensor, and control the fan with a wall switch.  Kitchen still cold.

I disagree with Brad that forcing the boiler to be hotter will overheat the house, because A) the extra heat will be given up by the toesters and the space thermostat will shut off the gas valve before the house is overheated.

I have cabinets all around the kitchen perimeter.  No room for more iron. I attached sketches of my system.

Ironman

You May Want To Re-Consider

If you try to force everything through the 1/2in line, you'll be cutting your flow down to 2 gpm or less. That's just enough to carry 20k btu's at a 20 deg. Delta T.  Do you think 20k btu's is enough to heat your entire house? Most 100 year old homes need closer to 120k btu's.



What Brad told you is exactly right. A fan coil (your toester) and c.i. rads from a gravity flow don't belong on the same zone (loop). He's an engineer that does this everyday for a living. I've got 40 years experience in the design, installation and service of HVAC and I'd think long and hard before i would consider disagreeing with Brad.

Brad White

Please feel free to disagree with me!

Bob/Ironman- thanks for the kind words!   But I do appreciate if not thrive on being challenged. I make plenty of mistakes, usually and often enough in the basics and being challenged, questioned, called on, is all part of the process. Sure, some of my "duh" moments stung in the moment, but that is how I learn, how we all do.



From my medic/EMT training, it was the same rote: "Learn one, do one, teach one, screw one". Besides, it is all about fluids and pressures; nothing is wasted.



Frankly and I mean every word I write, I learn and have learned far more from those with tools in their hands then with pencils. Going back the 34 years I have been in this business, it has more often been the contractor who took me aside and showed me how things go in, how they happen, what space is required, that have stuck with me.



I am fortunate to work for and with the very same handful of engineers I started with and take nothing away from them. But the folks in the field who really are on the line with tools, time and a clock running, have been my mentors too and still are. 



Equally fortunate that I am reasonably intelligent, curious and connect the dots. But it was not until I came to this great site and through Dan and others subscribing here, that I felt a flourishing and compounding of teaching, learning, learning some more.  I am indebted to all of you.

Ironman

That's The Difference

Brad,



That's what's such a refreshing difference between yourself and the typical engineer that alot of us deal with regularly.



 I don't want to paint everyone with the same brush, but quite often we're treated like ignorant peons to even dare question anything an engineer designs. And I've seen things designed, spec'd and installed that a first year tech would know were wrong. But to try to get the engineer to see it was as though you had question the wisdom of God. The last time that I checked, there was only one perfect Being in this universe and He didn't have a corruptible body.



And like yourself, I have gained a tremendous amount of knowledge and help from those on this site as well as from Dan's books. I've also had the privilege of putting that knowledge into daily practice and seeing it work.



Thanks to you and all who contribute here and to Dan for the help we all benefit from.

Mikey1970

This is my present setup

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     |  BOILER |                     |              |                  |                  S 

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Mikey1970

Thanks guys for the discussion.

OH I GIVE UP!! 

Let me try to state in words what I want to do:



Coming out of the boiler, I want to pipe two Toesters, in parallel with each other. 

Then back from the Toesters, I will pipe that return line TO the radiators.

In the boiler room, I will have a control valve of some sort connecting the boiler output to the TO the radiators pipe.



The control valve will operate as such:

Fully open: There is zero pressure drop across an open valve.  The Toesters will not receive any low.  This is the Brad scenario.



Fully closed: All water will run through the toesters first.  The Toesters might restrict the flow of the system.  This is the Ironman scenario.



Part open:  The pressure drop across the valve will cause flow through the Toesters, much like a monoflow tee.  The Toesters get water 100% the boiler.  The radiators get water that is part boiler, part (Toester with some of the heat taken out of it).  My circ runs constantly.  My tstat controls the gas valve. 



The gas valve will cycle enough to keep my living room tstat satisified.  That means my living room radiator water is the same temperature as before I repipe as I am proposing. That also means that my boiler output is necessarily hotter.  That means my Toesters put out more heat.



Will the part open valve do what I am stating?

Mikey1970

OK, that really looked better on my screen!!

I promise I only hit the submit button once!

What I was attempting to show is that at present, the cast iron radiators are all laid out in parallel like rungs on a ladder lying on its side.  The toester is waay at the end.

What I propose is to place two toesters in parallel , and then place that in series with the cast iron rads. 

I tried to show that to prevent ALL the boiler flow from going through the toesters, drew one valve to "short circuit" the toester path, or one to throttle it down entirely.

Also, there is 1/2 copper inside the toester, but 3/4 supply.  I definitely plan on adding the second toester, so that improves the flowrate situation somewhat. 

Am I making sense? 

Brad White

Believe it or not,

It actually is clear.

But I still think you will not be happy with the outcome.



The cast iron radiators have next to no pressure drop and get first pick. Water is your hydraulic teen-age son.

(See my "truism" statement below.)



The flow rate through the toe-kick heaters will not be above the minimum flow rate required to be above laminar flow. In English, water will slowly coast down the middle of the pipe and not rub itself on the walls where heat transfer occurs. So even if your hydraulic teen-age son gets off the couch, the refrigerator is next to it, so why go find the lawn mower?



Your toe-kick heaters still have low mass. The thermostat which controls the cast iron main zone will be satisfied and even if your toe-kick heaters have direct fan control, the water flow and temperature will drop off between cycles. The toe-kick heaters will be cold.



Here is a little truism about pressure drop in a hydronic system:

All branch pressure drops are equal. Even without balancing valves, the pressure drops are equal. This is because they settle at a balance point of flow and the effort to create it against the piping.



This does not mean that the system "balances itself" for our purposes. It just means that the pressure drops are equal, but only at the flow rate the system will allow. And the toe-kick heaters will not be allowed much.



Thus you can see if water has a choice between a 1.25" iron pipe and a large-passage radiator close to the boiler and necking down to a 1/2" pipe with serpentine coil, the iron gets first pick. You will get "some" flow through the toe-kick heater but nothing approaching a performance level.



Flow is forgiving when near the design range, but I fear that the flow rate through your toe-kick heaters the way you intend to do this will be dwarfed by your tears in this case.



Dedicated pump and boiler control for the toe-kick heaters, mixing valve on the CI system (with outdoor reset, why not?), and enjoy.



My $0.02



Brad

Mark Eatherton

Nice Bradism....

Here's a Markism.



Water is like my ex brother in law... Wet lazy and stupid. He LOVED to water ski, so much that all he did from ice off to ice on was hang out, looking for a ride to go water skiing. All he wanted to do was go in circles, and avoid work.



Your heating system is essentially the same. It just wants to get back on the boat (pump) and go for another ride around the lake (loop) and it ALWAYS follows the path of least resistance (lazy and stupid).



I know that in your minds eye, because you have everything hooked up, it SHOULD work, but you have a LOT of things working against you, and these things are overwhelming.



Way back when, when I first got involved in hydronics, I had a job in an older home (1905) that was a converted gravity hot water with a bunch of standing cast iron radiators. The owner wanted to get rid of the radiators on the 3rd floor and replace them with toe kick heaters. He didn't want to re-pipe the system. Just wanted to connect the new to the old and let 'er rip.



Looked like it should work to me. The system had been retrofitted with a pump, so we went forward with the plan. Bad news. The primary house thermostat never stayed on long enough to send hot enough water to the toe heaters. It felt "warm", but never got HOT. In frustration, we eliminated the coil mounted snap disc and replaced it with a line voltage thermostat, to no avail. It just made matters worse because it blew cold air around ALL the time.



In desperation, we installed another circulator to help move water through the coils, still no love...



The owner never paid us for the work (rightfully so) and ended up having to install a bunch of electric base board to keep his plumbing from freezing.



Bottom line, it will not work the way you envision it. Sometimes, your gut has a tendency to mislead your brain. This is one of those scenarios.



Listen to Brad and the others. You need to isolate this high pressure drop branch from the low pressure drop radiators, and provide it with its own circulator and control logic (including a room t-stat for THAT zone) in order for it to work.



It is a different appendage, hanging out by itself, like a red headed freckle faced step child with pimples, locked away and no one (water) wants to play with it.



Don't make the same mistake I made. Run a separate branch from the load to the source, install a zone valve to serve that zone along with a zone pump, and install zone valves/pump to serve the needs of the high mass, low pressure drop system, and you will be MUCH happier with the results.



Tough pill to swallow, yes, but much better than having to choke on your pride and admit defeat.



ME

Mikey1970

Please see newly edited posts

for further explanation

Brad White

Flow go, temperature no

First a minor point. When your pump is on, any open valve will have a pressure differential across it. It will not be zero and you will have flow. The key point is, not enough flow to deliver the heat you need. A trickle. Some, but I doubt anywhere nearly enough. More cool air with fewer BTUs.



Now, temperature.

It does not matter if your toe-kick heaters are first in line or last. Short of losses from the mains en-route, all of your emitters will see the same temperature, essentially. It is not as if you are feeding in series through one emitter set and sucking the heat out of what the next one sees. Your piping diagram is in parallel and that means all see the same temperature within a degree or two.



Yes, your water will be hotter, warmer, when the burner fires more often. With cast iron, you have a unique set of emitter qualities: High mass, high radiant, low "volatility". When the burner shuts off, the time lag until the next cycle will be far greater than with almost any other emitter type I can think of. (OK, radiant in concrete, but we can all dream, can't we?). 



Your driving thermostat will be happy, taking a break, when there is still work to be done.



Your low mass emitters, the toe-kick heaters, are fast to heat (when you HAVE the heat) and equally fast to cool.



Your water temperature for cast iron will be typically less than what will drive a toe-kick heater. You may find de-rating tables but this presumes you will have that temperature predictably With your cast iron main zone satisfied, the burner will be off and the water temperature will drop away.



I understand the idea of pushing the limits, doing more with less. Be my guest. But if you want comfort, I think our collective device stands and has stood the test of time.

Mikey1970

pic attached

Brad said" It is not as if you are feeding in series through one emitter set and sucking the heat out of what the next one sees."



Yes, that's what I am suggesting.

The control valve will operate as such:

Fully open: There is zero pressure drop across an open valve.  The Toesters will receive very little flow.  This is the Brad scenario.



Fully closed: All water will run through the toesters first.  The Toesters might restrict the flow of the system.  This is the Ironman scenario.



Part open:  The pressure drop across the valve will cause flow through the Toesters, much like a monoflow tee.  The Toesters get water 100% the boiler.  The radiators get water that is part boiler, part (Toester with some of the heat taken out of it). 

Brad White

But

is there a thermostat in the toe-kick heated zone which calls the boiler on separately from the rest of the house and closes the appropriate valves?



It will work IF the toe kick zone is the only one calling and you drive the boiler to sufficient temperature.



But once the cast iron zone again calls, the valves open and the cast iron zone will see at least one burst of the hotter water generated, then things will revert to the Brad Scenario, satisfying the CI zone while the water temperature is not enough to drive the toe kick heaters to their specifications.



If I understand your setup is as I described above, with the toe-kick zone being able to establish its own priority, then when it calls again (and it will), the valves will shut and deny the CI zone for the duration. I see a lot of cycling of this sequence, bouncing back and forth between competing priority zones.



Did I gather your situation correctly?

Mikey1970

The proposed system has no brains

Brad

There is only one tstat, in the living room.

The valve I drew in is a manual valve.  I need to read up on what valve to use, but I am hoping for a set and forget situation, where the valve is part open all the time.

Brad White

Then

there is no improvement, no reliable situation that I would recommend and call it comfortable.



Yes, you will have more flow but at an unreliable and likely too-low temperature, hence my "flow go,  temperature no" post title.



Go for success! For the effort of cutting in valves, you can put that toward running some 3/4" copper pipe to serve both of the heaters, a relay and circulator.

I can only lead you to water and only have your comfort and success in mind.

jp_2

buffer for toe kick?

wouldn't the big ol boiler short cycle just servicing a toe kick?



what if you added a buffer tank for the toe kick? and a pump too of course.



could use a 20 gal electric  tank. and maybe plug it in to even out the lulls.