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Replacing Cast Iron Radiator with Toe Kick Heater

As part of my kitchen renovation we want to take out a cast iron radiator (calculates to about 7200 BTU) under the kitchen sink and I had planned to replace it with a toe kick heater. However, when I talked to tech support at Turbonics they recommended piping a separate circulation zone for the toe kick heater.

They explained that when my heat cycles off the cast iron radiators still radiate heat for quite a while, but the toe kick heater will cool off in just a few minutes. They recommend setting up a separate zone and pump for the toe kick heater so you can selectively add heat. Is this a typical requirement for this type of heater? It certainly complicates the setup since my kitchen is at the opposite corner of the house from the boiler in the basement.

I don't want to renovate the kitchen and find out I've made it the cold spot in the house. I'm located in Virginia outside of DC, so most winters we don't have extremely cold weather.

System info: I'm using a 1 year old Buderus GC-124 natural gas boiler and Honeywell setback thermostat, and I'm happy with the performance. All radiator pipes (1940 vintage) run around the perimeter of the unfinished basement and up to the first and 2nd floors. The house is only about 650 sq ft per floor. There is a single circulation pump for the entire system.

Any suggestions or alternatives to running a separate line to the toe kick heater? Will I have a cold kitchen if I don't put it on a separate circulation pump?



Re: Replacing Cast Iron Radiator with Toe Kick Heater

Put it on a separate zone. Even after the thermostat is satisfied and the circulator shouts down the cast iron radiators will continue to produce some heat. Keeping the house warmer for a longer period than the toe kick heater which will stop producing the heat right after the circulator shouts down.

Re: Replacing Cast Iron Radiator with Toe Kick Heater


I would recommend you do a lot more research & exploration of your current system before you think about making any changes, this goes especially if you are thinking of this as a diy project; I would especially recommend you consult the Yellow Pages under "Heating Contractors" and get at least 2 installers over the house to give you THEIR TAKE on how it should be done, & a written dollar quote---be sure to read the display ads in the YP to find HCs who specialize in hydronic (hot water) heating systems---I'm not saying you actually need HIRE anyone if you're set on DIY, but you'll be surprised at how many different ways this project can be done, and naturally you want the most low-cost option that will provide good heat for the kitchen.

Could you provide more info as to your system----for example, what are the MAIN HEAT DISTRIBUTION PIPES made of (the pipes that go to & from the rads; (copper/galvanized/steel/Pex plastic, etc.) and what is their diameter; if these pipes date back to 1940 & are along with the near-boiler piping made of large black-coated steel, it could be quite expensive to go the route of a zone valve, which would require dedicated piping all the way from boiler to the kitchen KSH with its own circulator for one zone, and also considerably changing the near-boiler piping with flo-chek valves to put the rest of the house essentially on a 2nd zone.

Could you post the LxWxH of the rad to be removed, & also the LxWxH of the kitchen; any other calcs you have of ceiling height , general geographic location, # and total sq.footage of the kitchen windows & amt of insulation inside kitchen walls would be appreciated.

Google "room heat loss calculator" to get sites that help you determine how much btu/hour capacity you will need for your new convector(s); make sure the site takes into consideration your general geographical location, and other factors listed above; a very rough estimate of how may BTUs/hour you will need for your kitchen is to assign anywhere from 30 btu/hr to 50 btu/hr to each sq.ft. of kitchen space for your total kitchen btu/hr heat loss on a cold day; thus, if your kitchen is 400 sq.ft, has some insulation in the walls, is in a moderate climate, has one or two windows, & an 8' ceiling you will need a convector (radiator) rated at approx 12,000 btu/hr (30 btu/hr X 400 = 12,000 btu/hr) to adequately heat the kitchen; if there is less insulation in the walls, your climate is very cold, there are many kitchen windows/doors, you will have to multiply the 400 sq.ft. by 35, 40, 45, etc. to estimate the needed btu/hr output of the heating convector(s) (radiator, KSH, floor vectors, SS rads, etc.) you will have to buy or have installed to heat the kitchen; the Columbia site below will help you calculate the output of your present kitchen radiator; always check the boiler temperature gauge to determine heating system water temp---the closer it gets to 180 degrees when running, the better; there is often a lot of gallons of water in older piping systems---this mixes with the hot water from the boiler when the system calls for heat; the mixing of the cold water in the large pipes with the hot water being made by the boiler makes it much harder (and takes a longer time) to get the circulating water hot enough (180 degrees) to provide good heat to the rads (and the rooms), especially for the rads that are located far away from the boiler.

One experiment you can do is to wait for a cool nite & turn off the AC & turn up the heating T-stat to 80 degrees to turn on the heat & wait by the kitchen rad until you feel it heat----grasp the supply/return piping on either side of the rad base to see how long it takes for them to get hot enough to make you pull your fingers away quickly---if you have to pull your fingers off right away, you've just experienced 180 degree hot water (which is what it should be); in some older systems, there's so much standing cold water in the pipes when the heat & pump come on, that the system never gets to adequate temp to satisfy all the rads; if the pipes are hot enough, & the old rad did an adequate job of heating the kitchen, you can probably get away with using passive heat convectors, such as the KSH, floor vectors (Beacon-Morris), a short length of cast iron baseboard, the newer stainless steel radiators (Hydronic Alternatives) that are only 3" thick, or even under-floor high-temp radiant, to name a few options.

The sites below are listed only for informational purposes; Beacon-Morris tends to be pricey; at the first BM site they have convector charts that relate to steam rads & hot water rads; many of these units are designed for garages & storage applications---only the HW charts are relevant; the forced hot water piping diagrams at the end of the site are worth saving; you would also have to shop around for those stainless steel rads that have come down in price in recent years; always Google the general term of these products ("hydronic floor vector", "stainless steel hydronic radiator") to get a wide price/style selection; a photo of a floor vector can be viewed at the 2nd BM site by clicking onto "other Beacon-Morris products" or "Products-Residential at the top of the page; floor vectors can be mounted horizontally (in floors) or vertically (in wall cavities), which are good for tight-space areas like kitchens; numerous mfgs make similar vertical stainless steel rads for kitchens.


Re: Replacing Cast Iron Radiator with Toe Kick Heater

I disagree with the previous post. To run a toe kick heater all that would be required for the piping would be to pex lines one feed and one return. He has a fairly new boiler so I'm sure there are copper lines at the boiler that would be very simple to connect a circulator and a flow valve to.

Re: Replacing Cast Iron Radiator with Toe Kick Heater

I appreciate all the comments, but maybe need to make a few clarifications. I am not trying to make a do-it-yourself improvement. I had the boiler replaced and converted from oil to natural gas last November by a licensed heating contractor. I had the same contractor come back in a couple months ago and install A/C using an attic-mounted unit and standard size A/C ducts. In both cases I did a lot of research ahead of time and everything worked out very well. As part of my kitchen renovation I'm trying to do the same type of pre-contract research.

During the kitchen renovation there will be no increase in floor space, but it will include a bigger opening to the dining room and much larger opening to the living room. Its basically a conversion from a 1940's floor plan to a more open floor plan. The entire 1st floor is about 640 square feet, and the kitchen is about 130 square feet of the first floor. The existing heating on the 1st floor has 4 cast iron radiators (kitchen -1, dining - 1, living - 2). My gas boiler temp is set to run about 145-150 degrees, from what I remember seeing during the winter. The gas boiler is new, but is a fairly standard .84 efficiency Buderus, using a Grundfos circulation pump.

The existing kitchen radiator is under the sink and if I leave it there I won't have space for a garbage disposal. I doubt I will have floor space to use another type of radiator somewhere else in the kitchen. I don't want to use baseboard heat both because of how it looks (not much like 1940) and because it has the same performance problem as a toe kick (cools too quickly compared to a radiator).

If I need to add another zone for the toe kick heater that should not be a major expense, however, I just want to verify this is what is typically needed when you mix a toe kick with cast iron radiators. The existing cast iron pipes run around the perimeter of the basement (about 21x30 footprint) and the boiler is therefore about 60 feet from the kitchen radiator. If I add another zone I assume I will need to add another pump, zone controller, and about 50-70 feet of pipe. It is all running through unfinished basement, so it should not be that complicated.



Re: Replacing Cast Iron Radiator with Toe Kick Heater

All proper hydronic designs and alterations begin with an ACCA Manual 'J' heat load. We avoid toe-kicks when ever possible as they are not radiators and lack the comfort thereof. We prefer to install radiant ceilings, walls or floors, sometimes in combination, to equal or exceed the original efficiency and comforted afforded by the old cast iron radiator.

In fact we turned down a design/build remodel, which included substantial hydronic work, but when the architect insisted on a toe-kick in the master bath, we said; no, we won't. Thanks anyway.

Make sure to give the old radiator to someone you love...

Re: Replacing Cast Iron Radiator with Toe Kick Heater

I agree that "All proper hydronic designs and alterations begin with an ACCA Manual 'J' heat load." (which has been done once already), but that's like saying "All proper brake jobs begin with a complete assessment of the car's braking system." - Its a true statement that's not really an answer to any particular question.

If I assume toe kick heaters won't work well as a radiator replacement, will any of the modern replacement radiators work effectively? The existing radiator is 7 tubes deep, but only 17" high. There are newer radiators that have fewer tubes but are much taller; however, they appear to be much lighter construction that would not have the same heat retention characteristics as an old cast iron radiator. Will I have to find an old cast iron radiator to make a direct replacement?

With respect to your last comment, I plan to keep the old radiator for possible future use. My basement is unheated and I may want to add some heat in the future. However, I may not get to projects like that for several years.


Re: Replacing Cast Iron Radiator with Toe Kick Heater

I did this in my kitchen remodel, and it actually heated better than the 400lb monster it replaced. If you have a circulator pump, the built-in control in the toe kick heater will cycle the blower fan on/off when the water coming in is at a suitable temp. I keep the 2-speed fan switch on low, so the cycles are slower, as less heat is transferred off the coils.
Mine is a Myson, they come in two sizes, the heat loss calc. for the kitchen informed me I could use the smaller model, and it's been great. Don't miss the space-grabbing boat anchor at all.

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