Recessed Cast Iron Radiators

BennyV

I'm in the market for a house, and many of the houses I'm looking at were built in the 1930's and have recessed cast iron radiators. These radiators are gorgeous, very compact (since they are recessed) and appear to be good candidates for a modern gas condensing boiler with outdoor reset. However, I have a few questions about how they are insulated and operated in a modern environment.

1. Do they have any insulation behind them? Are they a massive disaster for heat loss?
2. Most houses with cast iron radiators don't have central AC. I would put in Mitsubishi mini-split heat pumps to get AC. Although I'd probably use gas when it's well below freezing, if I was running on heat pumps at design temps (around 0 in southern New England), are the recessed radiators at risk of freezing? Do they need Cryo-Tek added to the hot water system to avoid freezing? How much of a disaster for heat loss and comfort do they become during extreme cold weather when not operating? I'm thinking I'd want to run on gas below 20F OAT, but if I'm away and a cold snap hits or the gas boiler or pump has a problem and is shut down until the cold snap is over, the radiators would be sitting dead.
3. Many houses have been added on to, and the add-ons usually put fin-tube into the loop with the cast iron radiators. If it is relatively open between the two areas, do they balance out? I can't imagine that the heat is ever going to balance out well, especially on outdoor or indoor reset where the fin-tube's heating curve is totally different than the cast iron's. I suppose it doesn't really matter, as the heat pump in that room could make up the difference anyway if there's not enough heat, and if there's too much, just close the damper on the fin-tube?

Jamie Hall

Presuming you are looking at hot water heat. But please note -- not all recessed radiators were or are hot water; steam was not uncommon. But if hot water...

No, there usually isn't much insulation behind the recessed radiators. For that matter, there may not be much insulation anywhere. And yes, they do lose heat through the outside walls, so as is they aren't as efficient as they might be. They aren't a disaster, though, and it may be possible to slip a reflective sheet behind them which helps a good deal.

If the house is warm or warmish, and stays warm, they usually aren't at risk of freezing unless the power is off for a good long time. The domestic water plumbing -- which is often on the outside walls, too -- is at every bit as much risk. That said, adding a propylene glycol antifreeze to the system certainly can be done for peace of mind. It does make working on the system a bit harder.

Fin tube does not play well with cast iron, and ideally would be on a separate zone. That said, it can be made to work well enough.

leonz

BennyV said:

I'm in the market for a house, and many of the houses I'm looking at were built in the 1930's and have recessed cast iron radiators. These radiators are gorgeous, very compact (since they are recessed) and appear to be good candidates for a modern gas condensing boiler with outdoor reset. However, I have a few questions about how they are insulated and operated in a modern environment.

1. Do they have any insulation behind them? Are they a massive disaster for heat loss?
2. Most houses with cast iron radiators don't have central AC. I would put in Mitsubishi mini-split heat pumps to get AC. Although I'd probably use gas when it's well below freezing, if I was running on heat pumps at design temps (around 0 in southern New England), are the recessed radiators at risk of freezing? Do they need Cryo-Tek added to the hot water system to avoid freezing? How much of a disaster for heat loss and comfort do they become during extreme cold weather when not operating? I'm thinking I'd want to run on gas below 20F OAT, but if I'm away and a cold snap hits or the gas boiler or pump has a problem and is shut down until the cold snap is over, the radiators would be sitting dead.
3. Many houses have been added on to, and the add-ons usually put fin-tube into the loop with the cast iron radiators. If it is relatively open between the two areas, do they balance out? I can't imagine that the heat is ever going to balance out well, especially on outdoor or indoor reset where the fin-tube's heating curve is totally different than the cast iron's. I suppose it doesn't really matter, as the heat pump in that room could make up the difference anyway if there's not enough heat, and if there's too much, just close the damper on the fin-tube?

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Your in the early stages of this mess so just wait:

Question 1:
Does your realtor really know anything about heating systems?
If not, I would find another realtor that knows something about heating systems other than saying "that thing has to go!!!!"

Do you know whether the heating system in any of these homes are using a gravity hot water heating system, hot water circulation or one or two pipe steam?

If they are a one pipe steam system which is the simplest to own and operate they will not have a pipe coming off the opposing end.
Gravity hot water systems are the simplest whole house heating systems with smooth even heating for all rooms that do not require forced circulation of hot water to heat the living space.

Properly maintained steam heating systems are also very good heating systems.

Both gravity hot water and steam heating systems are very efficient so no worries there.

Too many homes that have good usable gravity hot water and steam heating systems have been ripped out for air conditioning and that is a terrible mistake that is very very hard to undo.



Question 2+3: if you have recessed radiators chances are the system most likely is a steam heating system.

If your seriously interested in specific residence hire a good plumber from the "Find A Plumber List" here on the forum then hire a steam plumber for 2 hours work, buy his or her lunch or dinner and let them explain heating and cooling to you, listen to them intently take notes, purchase the books on heating that Dan Holohan has written from the bookstore here(all profits go to Dan directly and he ships the books to you and you can honestly say you know more about heating so you can enter into the purchase of a steam heated home which is most likely what you have been looking at.

DO NOT AND I REPEAT and do not listen to the realtor under any circumstance!!!!!!!!!!!!!!!!!!!!! burned once twice shy dealing with those people.

BennyV

Many good points. Most are hot water. I've seen a couple of steam systems. In a smaller house, I don't want steam, as it takes up too much space in the basement, and it's not easy to just add on zones for finished rooms in the basement or additions, versus a FHW system where the boiler, oil tank (if on oil), and any offending piping can be removed and replaced with a wall hung natural gas boiler that can be tucked out of the way. Most of the hot water setups are forced hot water, I'd imagine some of them were originally gravity hot water. I have no interest in forced hot water, again due to eating up too much space in the basement.

BennyV

leonz said:

Question 1:
Does your realtor really know anything about heating systems?
If not, I would find another realtor that knows something about heating systems other than saying "that thing has to go!!!!"

...

Too many homes that have good usable gravity hot water and steam heating systems have been ripped out for air conditioning and that is a terrible mistake that is very very hard to undo.

She's more of the opinion of "if it ain't broke don't fix it". She deals with a lot of older houses. That being said, few realtors know the details of heating systems. I am specifically looking for a house with cast iron hot water radiators, because I like the style, and I don't really want central AC anyway. Mini-splits are cheaper and more efficient versus paying more for a house that someone else did a crappy job putting central AC in.

What does concern me is that some houses seem to have had some of the cast iron radiators removed and replaced with fin-tube, which is a lousy hodge-podge. The CI rads either appear to have gotten in the way of remodeling, or maybe broke and had to be replaced, so they went to Home Depot and bought fin-tube. Other houses have all their original CI rads, but breezeways, family rooms, and porches were added on later using fin-tube, which is less of a concern to me.

In terms of steam, I'd strongly prefer hot water, and that's what 95% of the houses have, amongst the ones that don't have scorched air. Some are actually 1940's as well, and from the late 30's through the 40's, they were either doing hot water in these types of houses, or they were steam, and have been converted to hot water at some point.

BennyV

Correction: I have no interest in *gravity* hot water. I want forced hot water.

I'd be fine converting a system from gravity to forced while replacing the boiler. Most of them have old CI gas or oil boilers. A modern wall-hung gas condensing boiler will take a while to pay for itself in terms of gas usage, but it would pay for itself instantly in terms of space savings and flexibility in using the basement space.

Jamie Hall

The trick with getting a mod/con to pay for itself is persuading it to condense -- which means low return temperatures. You may not be able to achieve that -- or come even close -- unless you reduce the heat loss from the house substantially. Otherwise they are just high maintenance, high capital cost hot water boilers...

leonz

BennyV said:

Correction: I have no interest in *gravity* hot water. I want forced hot water.

I'd be fine converting a system from gravity to forced while replacing the boiler. Most of them have old CI gas or oil boilers. A modern wall-hung gas condensing boiler will take a while to pay for itself in terms of gas usage, but it would pay for itself instantly in terms of space savings and flexibility in using the basement space.

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Don't make your problems worse; Both steam and gravity hot water heat are very efficient heating methodologies. The age of the boiler and its operating efficiency are the major issues in your case.
Why would you want to change gravity hot water it if you can still use panel radiators and simple baseboard heat to add heat in places?

"Find out what kind of heating system you have in the specific house you want"; then hire plumber for an hour to look at it.
if its a steam heated house you will need to do a lot of work and spend a lot of money to change it to hot water heat.

IF you have steam heat in this house you will spend a huge sum to change it to hot water heat when you could simply move the boiler to a corner of the basement in an insulated room to cut down on the burner noise if that is an issue.


You can purchase cast panel radiators to deliver steam heat effectively where you want to install hot water baseboard heat.
I am unsure if you can use the cast baseboard for steam but I am sure that one of the fine members here will let me know if it can be done.

BennyV

Jamie Hall said:

The trick with getting a mod/con to pay for itself is persuading it to condense -- which means low return temperatures. You may not be able to achieve that -- or come even close -- unless you reduce the heat loss from the house substantially. Otherwise they are just high maintenance, high capital cost hot water boilers...

Part of the key here too is space savings... Even if a 15% more efficient boiler will take a while to pay for itself, the space and location of most of them eats up a lot of real estate for using and finishing off the basement, especially since they need to be near a chimney, versus PVC direct venting on a modern boiler.

BennyV

leonz said:

Don't make your problems worse; Both steam and gravity hot water heat are very efficient heating methodologies. The age of the boiler and its operating efficiency are the major issues in your case.
Why would you want to change gravity hot water it if you can still use panel radiators and simple baseboard heat to add heat in places?

"Find out what kind of heating system you have in the specific house you want"; then hire plumber for an hour to look at it.
if its a steam heated house you will need to do a lot of work and spend a lot of money to change it to hot water heat.

If you have steam heat in this house you will spend a huge sum to change it to hot water heat when you could simply move the boiler to a corner of the basement in an insulated room to cut down on the burner noise if that is an issue.

You can purchase cast panel radiators to deliver steam heat effectively where you want to install hot water baseboard heat.
I am unsure if you can use the cast baseboard for steam but I am sure that one of the fine members here will let me know if it can be done.

The gravity systems I've seen out there are already running as FHW systems, as they have pumps installed in them. The older coal or oil boilers were removed a long time ago, often you can see their outlines on the floor where a much smaller (relatively speaking anyway) gas CI boiler is now residing. There's nothing mechanically wrong with using gravity piping with a FHW system, but the gravity piping just doesn't work for using the basement space, as it's hanging down too low, so in those types of houses, it would have to go, but that's a relatively minor change to put in copper or PEX along the basement ceiling and then go back to the original piping where it leaves the basement and heads upstairs.

With steam, it's still a real space killer, as you've got a huge boiler and a huge mass of piping, but luckily I've seen very few houses with steam, so it's likely not an issue.

Steam doesn't work for heating the finished spaces in the basement, however, as the radiators would be below the boiler, and that whole gravity thing... Also, steam piping is too obtrusive to use the basement space, whereas FHW you can hide 3/4" copper or PEX just about anywhere out of the way.

What might end up pushing me towards a newer house, however, are the basements. I have to have 7'6" basement clearance from floor to the bottom of the joists so that I have enough room for a drop ceiling and still have 7' of headroom, and a lot of the older homes don't have that. If I go newer than the 1950's, I have to compromise on the CI rads, as most of them moved to fin-tube at that point.

Jamie Hall

Actually, steam can be used just fine to heat the basement -- there is, after all, no regulation (yet!) which says that the radiators have to be at floor level...

Tinman

In my experience, most homes that are heated with hot water are over-radiated with an over-sized cast iron boiler lending itself well to a mod con boiler. The more the radiation, the lower water temperatures needed resulting in increased condensation. You'll need the right contractor for that though. Size the boiler to the heat loss of the home, determine EDR of radiators, and then an educated decision can be made.

BennyV

Jamie Hall said:

Actually, steam can be used just fine to heat the basement -- there is, after all, no regulation (yet!) which says that the radiators have to be at floor level...

I suppose you could... if you want cold toes.

Stephen Minnich said:

In my experience, most homes that are heated with hot water are over-radiated with an over-sized cast iron boiler lending itself well to a mod con boiler. The more the radiation, the lower water temperatures needed resulting in increased condensation. You'll need the right contractor for that though. Size the boiler to the heat loss of the home, determine EDR of radiators, and then an educated decision can be made.

That's a really good point. In that case, I would want to do the energy auditing and any envelope upgrades at the same time, and take that into consideration when setting up the reset curve on the boiler....

Is there any point in sizing a boiler in a modest size house where the heat load is <50k when the smallest available is either 7800-55000, 8000-80000, or 8500 to 85000?

EDIT: I should add, I want some small zones in the basement with fin-tube baseboard, so having a 10:1 TDR is a requirement so that I can have a pair of zones that are ~10k each.

Tinman

If you’re lowest turndown ratio (7800) gets you below the heat loss of your smallest zone, you’re good. That’s assuming that you’re using a low water content modcon. If you’re using one that has a high water content like a specific HTP or Viessmann, there’s really not much concern for short cycling.

Tinman

My first attempt at my post directly above sounded like Tommy Two Times from Goodfellas.

BennyV

Stephen Minnich said:

If you’re lowest turndown ratio (7800) gets you below the heat loss of your smallest zone, you’re good. That’s assuming that you’re using a low water content modcon. If you’re using one that has a high water content like a specific HTP or Viessmann, there’s really not much concern for short cycling.

For a basement, it would be more of a concern of the radiation in a small room versus heat loss, as there isn't a whole lot of heat loss, it just needs something to boost up the temp for a couple of hours from say 52 to 62 to use the basement room, and then it would be shut off again. I don't want to have to put in 30k of radiation, run high water temps, and cook the room in 3 minutes because the min fire rate is 28k. A heat pump would work, I just don't really want to have to pay for a heat pump for each little basement room versus a couple of baseboard zones. Plus, it wouldn't be a bad idea to run the boiler occasionally so that it doesn't just sit dead most of the winter, as the heat pumps will be heating the upstairs most of the time. I also don't want to spend a lot of money or space on a boiler that I'm not going to use very much.

Circling back to the houses, many of them have fin-tube baseboard as well. It's possible I'll end up going with a newer house with fin-tube, even though I really like the idea and look of cast iron- I'm just concerned about the lack of insulation on those recessed rads.

BennyV

Back to radiators, do the 1950's era American Standard convectors have the same problem with insulation? I find them quite ugly, and a detractor from the house, not a feature like the CI recessed radiators, but a lot of houses in the area have those, typically the ones built in the post-war boom, as opposed to the pre-war houses, or a few in 1948-1950 that seem to have been constructed like pre-war houses until building practices changed/improved/devolved/got more efficient/got cheaper depending on how you look at things.