In-Floor Steam Convector?

acwagner

We’re remodeling our tiny kitchen and I’m brainstorming on how to add steam heat to the room without sacrificing precious space. New layout will be a galley kitchen with a glass sliding door on one end and opening to the dining room on the other. No wall space to put a standalone cast iron radiator without sacrificing cabinet space. Calculated heat loss is tiny--around 2,500 BTU/HR, and that doesn’t take in account appliance heat loads. Rest of the house is Corto style CI rads.

Anyways, I’m trying to find examples of in-floor convector setups for steam. Anyone have photos of some they've come across? I suspect I’d have to make it myself, which I have no problem with. Thought would be to put it in the floor next to the non-operable side of the slider door.

Trying to avoid doing an electric toe-kick heater.

Hap_Hazzard

Do a steam toe-kicker. Put a convector in the floor under a cabinet with a grille open to the front. That way you don't even need to care what it looks like.

EdTheHeaterMan

Usually, Radiant Floor heat is low-temperature water in pipes in the slab or under the subfloor with lots of insulation under the pipes (or pex or hose or something else) to keep the heat from going the wrong way. I'm trying to think of a low-temperature steam system???

Can't think of anything.
How about a heat exchanger? A tankless DHW coil on the steam boiler
this boiler has a tankless coil on the right side

where you can build a radiant floor system using: Pex, a pump, an expansion tank, relief valve, mixing valve. basic and simple.

EdTheHeaterMan

If that is more complicated than you want to build, Electric radiant floor for the small space.
https://www.youtube.com/watch?v=iZfTnXlFIDY

acwagner

@Hap_Hazzard I thought about a toe kick setup. I was looking at Slant Fin bare elements. They require 10" of total height (min space below plus element) according to their technical documents. So, that would have to be in floor with the grille in the toe kick. I'm exactly sure how to get air floor to circulate with that setup, though.

@EdTheHeaterMan I'm not looking to do in-floor radiant, just a small convector recessed between the floor joists with grille on top, or something to that effect.

bvaughn76

@acwagner I would assume if you had a radiator between the joist mounted horizontally I would have the radiator boxed out. Put a board on either side of the radiator and then cover the radiator with a panel under it. Make a sealed enclosure. On the floor in the kitchen you would cut out a floor grate on one end of the radiator. Then in the basement side, cut out another grate on the opposite side of the radiator. You want to create a chimney effect drawing cold air up into the radiator which will draft into the kitchen.

Alternatively you could add a second floor grate on the kitchen side, but I dont know you will get as good of a chimney effect and you might get less airflow. If you did that, i would enclose the joist space further on one end of the radiator so there was empty space for cold air to drop into so it wasnt fighting heat radiating up.

acwagner

@bvaughn76 I'm thinking along those lines, but looking at using a convector element (1.25" steel pipe with fins). The basement below the kitchen has the boiler and water heater and I don't want to create a deliberate connection between the spaces.

I'm trying to figure out how to get the convective flow to naturally work, like you're saying. I was thinking of putting internal baffles so it has a flow path. Here's what I was thinking conceptually in a cross sectional view:



I just don't know kind of spacing is required to make it work right.

acwagner

I'm looking through my copy of "Notes on Heating and Ventilation" by John Allen that has a short section on indirect steam heating. Looks like there were some guidelines on a setup like this, but assumptions are for institutional steam pressures (5 psi operating) and a pin radiator.

According to his table a rough guide is cold air inlet cross section in square inches needs to be twice the size of the EDR of the heating element.

Any other references out there?

mikeg2015

I don’t think you need extreme precision here. Placing a slant fin element in a custom build Sheet metal box, they you’ll probably want to insulate around the outside with duct wrap. I think making it 6” wide to fit standard floor heavy duty floor grills would allow adequate flow so long as the elements is placed at least 2” above the bottom of the box. I suppose you could offset the element to one side to better encourage cool air to fall in.

I was considering something like this for my kitchen if we ever renovate it.

mikeg2015

... Other option is just placing the elements under the floor in the kitchen and panning it, then insulating it. My boiler room is under my kitchen and the floor is noticeable warm since the air is probably 85F at the ceiling. Also, the floor right above where I have fittings on the main, are noticeably warm.

Honestly, bare pipes without fins might work well enough. Could even make your own radiator out of black pipe, fittings and unions and hang it from the ceiling with Sammy’s and all thread. And again just using panning and insulation to contain the heat.

acwagner

True, I may be over thinking. But I also don't want to end up with a knuckleheaded P.O.S. that doesn't work as intended.

I'm reading through "A Practical Manual on Steam and Hot-Water Heating" and there's a rather extended rant about how natural draft indirect radiation is hard to get right.

It seems most of the indirect setups were used to temper makeup air that was coming directly from outside and use a duct/flue setup.

It all depends on quantity of air flowing through, and I don't know how to (yet) predict that with the setup I'm proposing.

Steamhead

Beacon-Morris "Floor-Vector"?

hot_rod

possibly just a bare steel pipe in the joist bay would provide enough BTUs/ hr.?
Suspended pex in joist bays was good for around 15- 17 btu/ sq. ft.

acwagner

I did find some guidance. "Handbook for Heating and Ventilation Engineers" by Hoffman/Raber has section on it. Here's a screen shot:



And, of course, Dan has a summary:

https://heatinghelp.com/systems-help-center/indirect-hot-water-heating-q-and-a/

acwagner

Thanks, @Steamhead! The "Floor-Vector" seems to be exactly what I was looking for. I could "borrow" the design and make something similar since it appears to be discontinued.

Their literature only has output ratings for hot water.

Question for anyone: is the output of a convector the same for steam and hot water at the same temperature?

acwagner

@Hotrod I assume your idea just having the pipe in the joist bay with no grille?

Steamhead

acwagner said:

Thanks, @Steamhead! The "Floor-Vector" seems to be exactly what I was looking for. I could "borrow" the design and make something similar since it appears to be discontinued.

Their literature only has output ratings for hot water.

Question for anyone: is the output of a convector the same for steam and hot water at the same temperature?

Steam ratings usually assume a temperature of 215° F- use that or something similar, interpolate if needed, and you should be good to go.

acwagner

I asked because when I look at baseray the hot water rating at 220 degrees is less than the steam rating at 215 degrees. Is that a function the radiant component of output or the convection component of output?

For my application it really doesn't matter if it's off a few hundred BTU's. Just curious at this point.

Steamhead

Interesting. Beacon-Morris' convector charts only go up to 210° F, but at that level they're not much less than the steam EDR ratings converted to BTU/hour............

mikeg2015

> @acwagner said:
> I asked because when I look at baseray the hot water rating at 220 degrees is less than the steam rating at 215 degrees. Is that a function the radiant component of output or the convection component of output?
>
> For my application it really doesn't matter if it's off a few hundred BTU's. Just curious at this point.

Could be that water entering starts at 220, but it exits at 200 or even 195 depending on flow rate. So the average Across the element is 210 Or less. Steam will heat the entire pipe to 215 depending on system pressure.

acwagner

That makes sense. The output varies on the flow rate according to the tables.

Interesting that the Beacon/Morris Floor Vector has the same cross sectional area for inlet and outlet air flow. All the older guidance has the outlet smaller than the inlet for natural flow.