Tech question on hot water heating?

[Kingcreek]

We have hot water radiant heat. In the middle of a bathroom remodel and had to eliminate a baseboard unit. Decided to replace it with a kick space heater under the new cabinets.
Problem: the old baseboard and everything else on the loop is 3/4" diameter but the kick space unit is 1/2".
Will that cause enough line restriction to reduce heating at other points?
Since 1/2 carries roughly half the volume as 3/4 I'm tempted to add another kick space heater under another cabinet and T to both and then T back to the 3/4" line. Make any sense?
Thanks

[K Frame]

OK, a bit confused...

Hot water radiant normally refers to tubes embedded in the floor, but you say that you removed a baseboard unit, which makes it sound as if your home has baseboard hot water, which is actually convection heat (but that's beside the point).

Anyway...

There are two ways of hooking up heating units.

The first, which isn't common but which is done in small homes, is in series. That means if you have 3 heating units, hot water flows through the first one, into the second one, then into the third one. By the time the water gets to the third unit, it's a lot cooler than it was when it went through the first one.

The most common way of plumbing a hot water system, though, is in parallel, where there's a hot water supply "main" with branches off to each individual heating unit, with the cooler water returning to the boiler either through a dedicated return main or, sometimes, through the same loop (the problem with that is similar to hooking them up in series in which the radiators nearest the boiler get the hottest).

If your system is hooked up in parallel, then it doesn't matter what the restriction is on your toekick heater, because it won't restrict flow through the main.


This page has diagrams that show the common ways of plumbing hot water systems.

https://www.diydata.com/planning/central_heating/pipework.php

[K Frame]

"Since 1/2 carries roughly half the volume as 3/4 I'm tempted to add another kick space heater under another cabinet and T to both and then T back to the 3/4" line. Make any sense?"

No. You've got a couple of considerations here....

First, you need to figure out the BTU capacity of the section of baseboard that you removed and match it to the capacity of the toe kick heater.

That toe kick heater may well be capable of meeting the bathroom's heating needs even with the smaller supply lines.

And remember, too, that the heating response from the toe kick heater will be faster because it's forced.

But, here's the kicker... you really want to put that toe kick heater on a dedicated thermostat to get the best control possible over heating in your bathroom. That way, if you like your bathroom warmer and the rest of the house cooler, you can control that easily. That might be a good application for a wireless thermostat.

But... that likely will require new control valves in the basement to allow the boiler to run and supply the bathroom with heat but not the rest of the house and vice versa.

[Hawkmoon]

We have hot water radiant heat. In the middle of a bathroom remodel and had to eliminate a baseboard unit. Decided to replace it with a kick space heater under the new cabinets.
Problem: the old baseboard and everything else on the loop is 3/4" diameter but the kick space unit is 1/2".
Will that cause enough line restriction to reduce heating at other points?
Since 1/2 carries roughly half the volume as 3/4 I'm tempted to add another kick space heater under another cabinet and T to both and then T back to the 3/4" line. Make any sense?
Thanks

It depends on whether your system is an archaic 1-pipe system or a more effective 2-pipe system

In a one pipe system, it's a single pipe loop and each radiator section is in series. This means that the first unit in line gets hot water, the next gets slightly cooler water, the third gets water that's still cooler ... until the last one (if there are a number of units) basically gets cold water.

In a two-pipe system, it's like electricity in parallel. There's a supply loop, and a return loop. Each radiator (fin tube) unit pulls hot water out of the supply loop and discharges it to the return loop.

If your system is a one-pipe system, introducing a 1/2-inch section into a 3/4-inch system is going to make downstream performance even worse than it already is. If you have a two-pipe system, the 1/2-inch section won't have any effect on other units downstream.

[Kingcreek]

It's in series but the bathroom being discussed is the last one on the loop, single line off manifold goes through 4 baseboards before returning to return manifold. I have other zones with other thermostats and zone valves. This is a 8.5'x12' 3/4 bath with a washer/dryer. The shower and short end wall are on the north side of the house. Everything has worked great for over 20 years.
My other option is to add elements under the ceramic tile floor and hope to get the floor warm enough that way. I did that with the bigger master bath (9x18) and it has worked well too. 3/4" AL finned copper elements between each floor joist and then boxed in with 1/2" foil backed insulation board.

[K Frame]

"It's in series but the bathroom being discussed is the last one on the loop, single line off manifold goes through 4 baseboards before returning to return manifold."

In that case yes, it's going to affect the heating performance of the other units in that series. I would advise you against putting that particular unit in and finding one with 3/4" feeds.


"My other option is to add elements under the ceramic tile floor and hope to get the floor warm enough that way."

OK, essentially convert to radiant floor heat. If it worked in the other bathroom, there's little reason why it won't work in that bathroom.

The great thing about radiant floor heating is that you can be very comfortable with a lower overall room temperature because the heat is coming up and bathing your body. Friends of mine had a house with in floor radiant and even in the dead of winter the house was extremely comfortable with the thermostat set at 64.

[Kingcreek]

With the shower on the north wall, the original concern when we did it 20+ years ago was to have the baseboard on that north wall in the area of the shower. The wall is well insulated and there are a couple elements running under the floor perpendicular to the joists already but can can repipe to add more heat there.
The only way I see to use the kick space heater and not create a pinch point is to add another unit under a different cabinet and T off for a parallel flow. They have 2 fan settings. The zone for this bath also includes a guest bedroom and another small 1/2 bath.
I had to remove the baseboard unit because we added cabinets to the combo bath/laundry.

[Firethorn]

This page has diagrams that show the common ways of plumbing hot water systems.

https://www.diydata.com/planning/central_heating/pipework.php

You know, I'm looking at that single pipe loop, and it is the closest to my house, but what's up with the pipe being continuous?  How do you convince the water to flow through the radiators?  If I were to diagram my place, the radiators would be in line with the water pipes - IE for water to flow, it has to go through the radiators.  This works in my place because, let's face it, it's tiny and most of the radiators are around the perimeter of the house.  Once the system gets going, it's flowing water fast enough so that the water only drops about 20 degrees from a complete loop.  I have three circuits - garage, living room/bath, and bedrooms.  Bath tends to stay a bit warmer because it is mostly bedroom area, in the center of the house, but also gets heat when the living room does.

[Kingcreek]

Firethorn, what you describe sounds like mine. The hot water has no alternative but to go through the heating elements. Mine also works because none of the circuits are very big. My 2500 square ft house has 5 circuits or zones plus another for the garage (in floor pex)

[K Frame]

Google monoflow fittings.

Sent from my SM-G960U using Tapatalk

[K Frame]

Holy crap King... you can use monoflow fittings in your application.

It will take some additional pipe work but it will work and wont restrict flow in the main loop...

Sent from my SM-G960U using Tapatalk

[Kingcreek]

Lightbulb on!
Monoflo fittings. Why have I never heard of such wonders?
Thanks. The fix is within sight.

[K Frame]

What have you decided, King?

Make any inroads on this?

[Kingcreek]

The monoflo Ts arrived Friday and I just need to sweat it together. Spent a little time cutting in and laying it out yesterday between patching and sanding drywall and mounting some hardware etc. replaced a ceramic floor tile where the supply for the old baseboard came up.
It's going to be too nice to call it a mud room.
The info on the monoflo or diversion T fittings is the perfect fix. Apparently they have been around 60 years or more but I had never heard of them. Thanks.

[K Frame]

Just be sure to get them on the correct side of the flow or you will likely screw things up.

"Apparently they have been around 60 years or more but I had never heard of them."

Bell & Gossett introduced the monoflow T in the 1930s because the old gravity-system OS "scoop" fitting apparently created too much turbulence with the higher water velocities and smaller pipes in more modern pump forced hot water systems.

Taco offers similar fittings, which they call Venturi Tees.


Only advice I have is make sure that you have them pointing in the correct direction, on the correct side of the flow (regular T goes in front of the heater, Monoflow T goes after) and you have at least 12 linear inches of pipe between the fittings.

[Kingcreek]

Only advice I have is make sure that you have them pointing in the correct direction, on the correct side of the flow (regular T goes in front of the heater, Monoflow T goes after) and you have at least 12 linear inches of pipe between the fittings.

Right! They even have an arrow cast right into them. I have to take down some ceiling tiles to make double sure of the supply side.

[K Frame]

Does the toe kick heater have an air bleeder on it?

A few years ago the one toe kick in Mom's kitchen stopped working.

I thought the fan had crapped out and was resigned to paying for that.

When I removed the cabinet floor I realized that it had a bleeder, so I gave that a try and what do you know, it started working again immediately.

Those two in her kitchen were the first two I ever worked with. The house I grew up in was steam, and that house was cast iron radiators.

[Kingcreek]

No bleeder valve on the kick space heater and no easy way to get to it under cabinet and above floor. Under floor mount was an option but there is ductwork and a dryer vent competing for space. My circ pump seems to push pretty good volume and there is an auto bleeder on the manifold. I'm hoping it's enough. I haven't had to bleed air off the ground floor for 20 years and only a couple times in the walk up attic.

[K Frame]

OK, you should be OK, then. Bleeder valves are less an issue on newer sweated copper pipe systems. Far fewer places for them to lose water and suck air in, which was always a big issue with Mom's 100+ year old system.

Word to the wise, though. Figure out a way to modify the bottom of the vanity cabinet so that you can get top down access to the unit. This is important in a bathroom, where there's a LOT of lint generated, and doubly important if you have pets. The heat exchanger fins will eventually clog with lint/pet hair.

The design on yours may be different, but the ones in Mom's house could really only be cleaned by removing the top top housing to gain access to the fins.

[Kingcreek]

I considered cutting an access door into the bottom of the cabinet. Still could.

[K Frame]

Hey King,

You never came back to let us know how this worked out. Did you have adequate heat in the bathroom last winter?

[MechAg94]

Hey King,

You never came back to let us know how this worked out. Did you have adequate heat in the bathroom last winter?

He should have been able to unstick himself from the seat by now.

[Kingcreek]

Sorry this is so late. Didn't realize the thread was on life support waiting on my update.
Worked great. The under cabinet heat unit keeps the floor nice and warm in the area around the stool and shower.
We use the off/hi/low switch on the toe kick because for some reason that loop is an open loop or always hot when any other zone is hot. I have a zone valve on it but it is locked open because the underfloor elements for the kitchen are on it also. I could easily reactivity the thermostat and zone valve and I might. It's been that way so long I forgot why I did it.

[K Frame]

Well, if it's working OK, no real reason to mess with it.