Cast iron water radiator & condensing boiler?

Kenneth Young

I'm a homeowner having a hard time getting straight answers from contractors. I have a two story attached home with 6 cast iron water radiators on each floor. I heard about the great efficiency of condensing gas boilers. Can a condensing boiler be hooked up to cast iron water radiators? Or would a traditional boiler be a more efficient choice?

Kenneth Young

Cast iron water radiator & condensing boiler?

I'm a homeowner having a hard time getting straight answers. I have a two story attached home with 6 old cast iron water radiators on each floor. I heard about the great efficiency of condensing gas boilers. Can a condensing boiler be hooked up to cast iron water radiators? Or would a traditional boiler be a more efficient choice? Thanks in advance for your input.

R. Kalia_3

of course

There is no physical or chemical incompatibility between a condensing boiler and cast-ion radiators.

What you may have read or been told is that cast-iron radiators are intended for high-temperature water, and if the water is hot (above about 140F) you don't get condensing and so the condensing boiler doesn't run at peak efficiency.

This is a half-truth. Cast-iron radiators are traditionally operated with 180F water, but this is NOT a requirement. An "outdoor reset controller" will vary the temperature of the water so that it is only as hot as it needs to be for that day's weather. Even on the coldest day of the year, you may not need 180F water. With the water temperature barely hot enough, the water will flow almost all the time. (I bet it doesn't do that now in your house, even on the coldest day, and if it doesn't, that means your water is unnecessarily hot.) Apart from efficiency, continuous circulation also improves comfort (the room temp remains steady) and reduces noises.

But no one can tell you precisely how much efficiency you'll get in what weather from a condensing boiler; that depends on the water temperatures needed by your house.

Brad White_2

Cast Iron and Continuous Circulation

with TRV's on the radiators and you cannot go wrong (assuming the radiators are sized to give sufficient output at reduced temperatures of course). The temperature reset profile of cast iron radiators (operative root word: Radiant) is ideal.

Compare to fin-tube convectors (that move air but are concealed from line-of-site infrared paths) and you have lots of surface exposed to you.

I have a mix of small-tube cast iron and Runtal panels on continuous circulation with TRV's off of a Monitor MZ and love it. No FTR on the main house circuit but am putting some commercial grade bare fin in the basement on a separate circuit.

Kenneth Young

Thanks for the excellent replies - that clears up alot of confusion. We're insulating and putting in better windows so I bet we could run the system with lower temp water. I will ask for an 'outdoor reset controller,' TRVs, and go with the condensing boiler.

Plumbob

you're learning fast

> with TRV's on the radiators and you cannot go

> wrong (assuming the radiators are sized to give

> sufficient output at reduced temperatures of

> course). The temperature reset profile of cast

> iron radiators (operative root word: Radiant) is

> ideal.

>

> Compare to fin-tube convectors (that

> move air but are concealed from line-of-site

> infrared paths) and you have lots of surface

> exposed to you.

>

> I have a mix of small-tube

> cast iron and Runtal panels on continuous

> circulation with TRV's off of a Monitor MZ and

> love it. No FTR on the main house circuit but am

> putting some commercial grade bare fin in the

> basement on a separate circuit.

Plumbob

you're learning fast

> We're insulating and putting in better windows so I bet we could run the

> system with lower temp water.


Yes, what you'll end up with is an excess of radiation (which has nothing to do with radon in your basement). It's an ideal situation for a condensing boiler.

Also, make sure they don't oversize your boiler. Hack contractors (not the kind you'll find on this page) oversize to cover their ****, knowing their customers don't notice or care, but it results in lower efficiency. If your contractor arrives at a new boiler size by looking at your existing boiler size, or if he goes around your house counting up your radiators, find another contractor pronto!

Good ways to size boilers are (a) by doing a heat loss, but this is quite conservative and can give high estimates; (b) by looking at your current gas consumption data as a function of outdoor temperature, assuming you have it, and adjusting it downwards for the increased efficiency you'll get from your new boiler.

larry p

cast radiators

I Live in de. and I need to replace some radiators in my house. ware can I get them in delaware