Move Sunrad from inside wall to wall surface

KevinWyman

Thinking about ways to add central air conditioning to my colonial style house. I really love the radiant heat and don't want to give that up but I would like to insulate the walls (currently 1936 vintage with no insulation, plaster on metal lathe) to reduce my heating loads. Question is, could I move the radiators out of their recessed positions and mount on the wall? I know I could go with new panel radiators but trying to avoid that expense. I have thought about new fan coils to do both heating and cooling but there is no easy way to insulate the piping going to the second floor units plus pull a new condensate line. This could be done on the first floor via the basement, but really don't want air heating in the bedrooms.

Beyond that thinking about air to water monobloc with natural gas boiler backup and keeping some areas of finned tubed radiation and cast iron radiators for heat.

EdTheHeaterMan

Whatever equipment you have that is recessed inside the wall can be moved 4 to 6 inches towards the center of the room. It will heat the room with the same BTU capacity. If the cabinet that is recessed in the wall is unsightly when mounted 4 inches closer to the center of the room.(on the wall surface.) Then you will just have a cabinet built to make the radiator look good. After insulating all of the walls, those radiators will be oversized for the space they are heating. Then you can use a lower water temperature which will increase the efficiency of the existing heating boiler.

ethicalpaul

It will heat the room with the same BTU capacity.

I think it's likely that they will heat with greater BTU capacity once they are out of a cold wall recess, in addition to the lower heat loss after insulating. But that is easily fixed with enclosures, etc.

EdTheHeaterMan

A radiator has a rated capacity based on how it is installed @ethicalpaul If the enclosure is recessed in an uninsulated wall or if it is recessed in a cabinet recessed in an enclosure that is mounted on the exterior of an insulated wall will not change the amount of heat that the convection air current will emit. However the insulated room will need less energy to be heated. So the water temperature in that same radiator can be lower since the required BTU capacity for the room is lower.

My point being moving the existing radiator 4 inches will probably be the lowest cost option to get the wall insulated. Painting the metal cabinet may be all that is necessary. If the exterior of the cabinet is unsightly or has mounting brackets that are not easily removed, then, a couple of sticks of one by six pine can hide the exterior of the metal cabinet.

Of course, that assumes that the riser coming through the floor can easily be moved 4 inches towards the center of the room by opening up the floor above it or ceiling below it to install a connecting pipe that is 4 inches shorter than the current connecting pipe that causes the riser to come up through the floor on the outside of the wall as opposed to inside of the wall

So my question to Paul is: does splitting hairs on BTU capacity of radiator actually contribute to the original posters answer, or will a slight difference in BTU capacity be a dealbreaker in using the existing radiator 4 inches away from its existing position?

“For a difference to be a difference, it has to make a difference” Gil Carlson

ethicalpaul

Sorry Ed. I could have sworn you said that the radiators would have the same BTU capacity when they were moved out of the wall and into the room. That struck me as odd. A lot of times, I will put a question or opinion out there to increase my understanding as well as to try to limit errors getting out into the world.

EdTheHeaterMan

No problem Paul, I also made the assumption that the radiators are the convector type that have an enclosure that can be placed inside a wall or on the wall surface as many convector type devices are marketed. Assuming someone takes a standing cast-iron radiator and cuts out a cavity in the wall to install it, that would reduce that type of radiator capacity in pretty much the same way that a radiator cover would reduce the capacity of that same radiator. By comparing an enclosed radiator to a radiator that is not enclosed, the capacity would be different.

Chances are the original post is about the convector type radiator, and I’m sure that radiator is nothing that I would want to look at in a tastefully appointed dining room or living room, or even a lovely bedroom that one might see in better homes and gardens, magazine or architectural monthly.

As a side-note, I was just wondering if Bryan @archibald tuttle Has contacted you with an idea for a video where you try to blow a Taco 570 heat motor? LOL

hot_rod

With more insulation behind the radiator the heat loss to the outside decreases, so the win should be less heat loss= less operating cost. Same as a radiant slab with or without insulation.

However output of the radiator increases as the temperature around or behind it drops. so the radiator recessed with little or no insulation behind it could be adding more btu/hr to the room. Which of course it needs to to overcome that un-insulated wall dimension.

A good analogy is a radiant snowmelt. You can get upwards of 200 btu/sq. ft output.
But inside that same square footage output drops to 20- 30btu/ sq. ft as the ambient temperature is much higher.
∆T drives the output.

Long Beach Ed

Pull them out a bit and put a piece of foil faced foam insulation behind and on top of them where possible. You'll have to adjust the supply pipe locations which very well might make the cost/benefit of all this work unfavorable.

bburd

As @Long Beach Ed noted above, the small energy savings gained by insulating behind the enclosed convectors will come nowhere near the cost to move them out of their recesses to the surface of the wall, which would require changing the piping.

EdTheHeaterMan

@ethicalpaul, how can you disagree with @hot_rod's statement?
As I see it, all he is saying is that ∆T drives BTU output.

It is in all the literature from the beginning of time... At least the beginning of when rating radiators began.

A typical baseboard radiator has the same dimensions weather the water temperature is 220°F or 120°F. If you put that radiator in a room that has 65° entering air and you use a water temperature so the ∆T is only 55° the heater will transfer 210 BTU per foot. If you change that ∆T to 155° the radiator will provide 900 BTU per foot. The literature from just this one page in a catalog proves the point quite nicely.

ethicalpaul

This part I disagreed with:

so the radiator recessed with little or no insulation behind it could be adding more btu/hr to the room.

In a cold wall, yes, it could be giving up more heat, but not into the room

EdTheHeaterMan

ethicalpaul said:

This part I disagreed with:

so the radiator recessed with little or no insulation behind it could be adding more btu/hr to the room.

In a cold wall, yes, it could be giving up more heat, but not into the room

Picky, picky, picky

hot_rod

Unless the radiator is on the outside of the house wall, not recommended, all its output is into the room. On a cold uninsulated space, the transfer to the outside will be higher than in a better insulated wall. That is the gist of a heat load calculation and defining exterior wall assemblies.

ethicalpaul

A lot of its output would be to the cold outside wall, not into the room. But it doesn't matter much to the OP...they will benefit from insulating the wall regardless

archibald tuttle

if the house needs siding in long term trajectory, i would leave the radiators recessed and put an inch and half of foam over the sheathing on the outside and then reside. you have to work out molding details but i'm doing pretty well on a house that has 3 layers of siding on it already. that gives me space for the foam and siding without coming way proud of the molding.

@ethicalpaul still glad to blow up 570 for research porpoises although that probably violates the marine mammal protection act