Small Bathroom Emitter Replacement

Ekkridon

The situation:

Double masonry house in Toronto, Ontario. Most rooms have cast iron radiators - replaced the heat source with a combi-boiler and buffer tank. Tank aquastat is wired to the boiler and tank is kept (during the season) at 130 degrees.

House thermostat with remote sensors throughout the house also wired to the boiler kicks on a circulator out of the tank to a manifold and to several heating loops.

The bathroom is on a shared loop with an adjacent bedroom, both with cast iron radiators - the bathroom one based on 20 ft^2 of surface area had an original design output (at 180) of 3200 BTU/h which is 937 Watts. I've done a heat loss calculation and come up with 853 watts requires so that tracks. Room is 6.3 ft x 7 ft x 8.5 ft and I used a design temp of -10 C.

I'm looking to renovate the bathroom and would love to save the floor space the radiator takes up. I'll list the options i've thought up but i'm also happy to hear other ideas.

1. Kickspace heater mounted under vanity - the bathroom vanity has enough clearance below the bottommost drawer to allow for a kickspace heater
2. Tall vertical radiator on the exterior wall - instead of the existing rad which is about 8" deep, more with the clearance to the wall and the vanity - I could go with a flatter taller radiator
3. Big Flat panel rad - on the outside wall - but would need to effectively cover all the space below the window to allow for the depth clearance (would need to be a type 21 - I don't think there is space for a type 22)
4. In floor convector or trench heater
5. Wall convector that would be behind the open door and thus on the opposite side of the room from the window.
6. A towel warmer that would be basically nearly floor to ceiling to get the required output - but this would replace my existing electric warmer and effectively deny us warm towels in the non-heating season which i'm not wild about.

Trying to get up to nearly that 3200 BTU/H amount (or near to it since the renovation also includes plans for electric floor heat (Ditra Heat or similar) - but not as the primary room heat.

Any advice oh wise hydronic peeps?

EdTheHeaterMan

All those options sound good. So pick one!

hot_rod

if it was piped in series, with other cast radiators, a small kick space type may need a bypass or its own circuit.

There are all sorts of unique panel rads for bathrooms. Jaga has some unique ones

Ekkridon

Thanks hot_rod. Can I press on that a bit? What would determine that it needed its own circuit? I have adjustable flow from the manifold so I think I can balance it - but would replacing the adjacent bedroom rad with a panel rad or other more low temp designed emitter solve the problem you are anticipating?

Right now i'm looking at the Smiths Quiet One KS2006 (at normal fan speed) or the KS 2010 (counting on always using the low speed for the fan). What would be the consequence of the mixed emitter loop - I seem to remember hearing that it means that the room with the cast iron rad would get more heat than it does now - which actually wouldn't be a bad thing - that room already feels a little cold (north side, and obviously running at 130 instead of design temp of 180).

Thank you for your thoughtful response!

mattmia2

The cast iron will heat and cool more slowly so it will run a longer cycle and will take longer to start heating but it will continue to heat a while after the cycle ends. A low mass emitter will dump all the heat during the cycle for the most part. I suppose that could be somewhat helped with anticipator settings to run shorter cycles to stop before much of the heat is released from the CI. You could use a salvaged cast iron wall hung radiator or I don't know if @Nick_Castrads has the right end pieces and hardware to make a wall hung CI radiator.

Nick_Castrads

@mattmia2 we absolutely do wall-hung radiators. Various bracket lengths available to accommodate all radiator depths.

Ekkridon

So the effective impact of a mixed loop with a cast iron emitter in one room and a low mass emitter in a second is that the cast iron will effectively run longer becuase of its thermal mass? Is that the right order of things? So of the two rooms the one with the CI would get warmer? Or do I have it entirely backwards?

Nick_Castrads

@Ekkridon it's only a matter of timing - there's a lag while the cast iron heats up, and that lag is mirrored at the end of the cycle while the radiator cools. With a lower mass radiator, the emitter reaches temperature quicker and cools down quicker. It's like a sine wave compared to a square wave.

For the entire period that both emitters are at temperature, if they're like-for-like in terms of heat output then the room would be the equally warm whatever the radiator is made of.

mattmia2

If it were an entire house and one low mass emitter in a house full of high mass emitters i would say you're going to have trouble balancing it. i think you can probably do some things with a compromise between the 2 with only another emitter or 2 on the zone