Old duct work in house heated by hot water boiler? Huh?

Questions, answers and advice for people who own or work on houses built during the 20th century.

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triguy128
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Location: Keokuk, Iowa

Re: Old duct work in house heated by hot water boiler? Huh?

Post by triguy128 »

All the piping and radiators and labor needed ot isntall them definitly cost more than ductwork. Plus, you can get a furnace for around $1500 and another $1000 to put it in. But the time you add expension tank, valves, backflow, PRV, air eliminator, etc, a boiler will set you back at least $5-6k. Again ductwork won't cost you much more than running 2 sets of pipes. A single metal supply register costs $10 and can distribute up to 12,000BTU's . A cast radiator with that capacity costs around $500. Think a slant in baseboard with that capacity runs maybe $400. Radiant floor heat I think would run around $800. A radaitor alos consumes valuable floor space.


I'm thinking a boiler will run you around $12-14k for 10 radiators and piping for a larger home. A furnace only would run about $5-6k with ductwork.

With the boiler, I now need to drop another maybe $8k for central air using ductwork or a minisplit. With a furnace, it's abotu a $4-5k adder. Premium equipment and zoning might add anoher $4k... even more for zoning the hydronic system.

So you have $20-27k vs. $9-15k.

Do I think it's worth it. Absolutely. IF I built a new home or won the lottery and gutted at least the ceilings in mine, I would have geothermal radaint floor heat with small individual ducted fan coils to cool and suplemental heat in each zone along with utilizing a small amount of radiant cooling.
1925 Neo-Classical

Previous home - 1968 single story Ranch/Colonial, 1200sqft - 11 windows
Current home - 1925 2 story Beaux Arts Neo-classical overlooking the Mississippi River, 3200sqft - 48 Windows

csnyder
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Location: Grand Rapids, MI

Re: Old duct work in house heated by hot water boiler? Huh?

Post by csnyder »

We recently spent $15k to upgrade our boiler (though we did go with a premium brand [Viessman]), so I think $12-14k is probably too low for a new system, even one on the smaller side. There's a lot of labor involved in fitting all of those pipes.

In addition to increased comfort over a forced air system, boilers also tend to have much longer lifespans than furnaces. When we were house-shopping last year, we saw a few houses with their original 1920's coal-fired boilers, converted to burn natural gas. Those dogs had to be terribly expensive to run - I've heard estimates of <50% efficiency - but they last forever. Our 1970's boiler (rated at 80% efficiency) seemed to be going strong, and I expect our new boiler (complete with stainless steel heat exchanger) to go 40+ years as well, assuming that the electronics don't crap out.
Chris Snyder, WavyGlass.org

Texas_Ranger
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Re: Old duct work in house heated by hot water boiler? Huh?

Post by Texas_Ranger »

Well, as I said, probably economics of scale. Here you can get a boiler complete with all accessories (expansion tank,...) and even an indirect hot water tank for €3500, which is roughly $4.5k, and that's including installation. Pressed steel rads start at €29.99 for the smallest ones, for €100-200 you already get fairly decent ones (€1 is about $1.30 at current rates). If you don't use copper, you can get an entire house with up to around 1500 or even 2000 sq. ft (depending on insulation values) or an apartment completely done for €5000-6000. That includes composite piping, a combi boiler (wall-mount unit consisting of central heating boiler and tankless water heater), thermostat and all radiators plus labour. That's cheap though, you can get quotes for three times as much too, without any substantial differences in material quality.

The boiler itself is by far the most expensive component, followed by the radiators. Expansion tanks and other details are peanuts, I think when we replaced the failed expansion tank on our 1977 combi boiler we paid €40 for the tank itself.

Regarding the life span: systems with copper pipes and steel radiators are supposed to last around 50 years, some start to leak after 25-30. Post-WWII boilers are somewhat short-lived, particularly combi units. Our 1977 boiler was considered ancient when we replaced it last year, the usual life span for those beasts was more like 25 years I think. Modern combi units aren't supposed to last more than 15 years. We also have a 2002 unit which has the third main electronics board (€450 I think) and the second one blew some temperature controls, frying the heat exchanger (the water got hot enough to melt the solder). I don't know how well freestanding units for larger homes fare in this regard.
The bad thing with electricity : it almost always works.

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triguy128
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Joined: Mon Sep 12, 2011 9:41 pm
Location: Keokuk, Iowa

Re: Old duct work in house heated by hot water boiler? Huh?

Post by triguy128 »

You're also comparing a small apartemnts to a large homes here. When you drop the size of the equipment and installation, boilers start to gain some advantages.

Economies of scale do matter a lot too.

But maybe I was a little too conservative on hte piping costs.

Ultimately any way you cut it, it's still going to be more expensive as least here. If it wasn't builders would install more hydronics.

You also forgot the AC part. A larger part of Europe is a moderate climate and AC is optional, so of like some parts of hte West coast in the US.

However, you do find the popularity of radiant floor heat increasing significantly, so we may have a trend forming as howmowners re realize the advantages of hydronics.
1925 Neo-Classical

Previous home - 1968 single story Ranch/Colonial, 1200sqft - 11 windows
Current home - 1925 2 story Beaux Arts Neo-classical overlooking the Mississippi River, 3200sqft - 48 Windows

Texas_Ranger
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Re: Old duct work in house heated by hot water boiler? Huh?

Post by Texas_Ranger »

Well, with decent insulation the boilers I mentioned can probably heat up to about 4000 sq. feet on several floors. The smallest size combi boilers put out around 60k BTU/hr, going up to 90k. Above that you get to freestanding boilers that look more like US models (had to look up the conversion on the internet, over here boilers have a kilowatt rating, common sizes being 18, 24 and 27 kW). I don't know much about the prices of larger boilers, but I'd suspect they're at least twice as much as the combi units and you need all the extra stuff (pump(s), expansion tank, valves etc.).
Ductwork is probably fairly cheap because it's made of steel rather than copper, as copper is awfully expensive. As far as radiators are concerned, pressed steel and cast iron radiators are apples and oranges. I think you can easily pay up to €2k for fancier radiators here, but the basic ones are dirt cheap. That's one of those (picture snagged from Wikimedia commons)
Image

I definitely agree with you that the need for AC is one of the main reasons for the popularity of forced air heating, but my main point is that the high prices of hydronic system are probably also caused by the lack of popularity over the past decades rather than being a reason for it, but actually that's a vicious circle.
The bad thing with electricity : it almost always works.

http://whatapigsty.blogspot.com

triguy128
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Joined: Mon Sep 12, 2011 9:41 pm
Location: Keokuk, Iowa

Re: Old duct work in house heated by hot water boiler? Huh?

Post by triguy128 »

It probably has more to do with central AC. Once you throw that into a mix, forced air will always be cheaper.

IF you design a house right, you should need little or no heat at all. So yes, a 60k boiler should be plenty for a home under 4000sqft. I think we'd be smart as a country strategically to mandate maximum equipment sizes, rather than mandate mimimum insulation levels. It would force desingers and builders to do load calculation on the home, sort of like home automotive desingers have to factor in fuel economy when stylign a car. IT's can't be an afterthought or something ot eave to the powertrain engineers.

Then you do to demand pricing structures as a further incentive to reduce equipment size and overall consumption. Right now, the more you use, the less you pay, not the opposite. IN particular reducing peak demand is the biggest goal.
1925 Neo-Classical

Previous home - 1968 single story Ranch/Colonial, 1200sqft - 11 windows
Current home - 1925 2 story Beaux Arts Neo-classical overlooking the Mississippi River, 3200sqft - 48 Windows

triguy128
Posts: 708
Joined: Mon Sep 12, 2011 9:41 pm
Location: Keokuk, Iowa

Re: Old duct work in house heated by hot water boiler? Huh?

Post by triguy128 »

So I did the math. The EDR of the radaitors in my home are pretty huge. I calculate the total EDR of the original radaitors in my home was around 1400! SO with steam, we're talking 300k BTU of capacity if the flow control were left wide open.

I'm looking now at seeing what kind of mix I can have ot use the 7 remainging radiators in my home supplemented with froce air hydronic and a few kickpace heaters and/or fan coils. (See other thread). I think i can meet my heating load with just 140F water temps at design conditions, and still use a hi-lo set-up and 120F water in the forced air units and get a nice 30F delta T. WIth the boiler I'm looking at (or any mod-con that runs at 5GPM with the internal pump), that gives me about 75k BTU's. More than enough for setback...and I can still use outdoor rest and run cooler water temps most of the time.

So much you can do with hot water.
1925 Neo-Classical

Previous home - 1968 single story Ranch/Colonial, 1200sqft - 11 windows
Current home - 1925 2 story Beaux Arts Neo-classical overlooking the Mississippi River, 3200sqft - 48 Windows

csnyder
Posts: 74
Joined: Mon Mar 05, 2012 12:49 pm
Location: Grand Rapids, MI

Re: Old duct work in house heated by hot water boiler? Huh?

Post by csnyder »

Our mod-con runs great with our over-radiated system: With today's very cold temperatures (around 0°F), our water temp got up the way up to the high 130's, when the system was recovering from nighttime setback. Our most recent gas bill was $170 - just a tad higher than our previous house (less then half the size, about 1/4 the windows) would have been.
Chris Snyder, WavyGlass.org

triguy128
Posts: 708
Joined: Mon Sep 12, 2011 9:41 pm
Location: Keokuk, Iowa

Re: Old duct work in house heated by hot water boiler? Huh?

Post by triguy128 »

csnyder wrote:Our mod-con runs great with our over-radiated system: With today's very cold temperatures (around 0°F), our water temp got up the way up to the high 130's, when the system was recovering from nighttime setback. Our most recent gas bill was $170 - just a tad higher than our previous house (less then half the size, about 1/4 the windows) would have been.
So you have cast iron radiators then? OR fin tube?
1925 Neo-Classical

Previous home - 1968 single story Ranch/Colonial, 1200sqft - 11 windows
Current home - 1925 2 story Beaux Arts Neo-classical overlooking the Mississippi River, 3200sqft - 48 Windows

csnyder
Posts: 74
Joined: Mon Mar 05, 2012 12:49 pm
Location: Grand Rapids, MI

Re: Old duct work in house heated by hot water boiler? Huh?

Post by csnyder »

Original cast iron. The front half of the house is tremendously over-radiated. The back half is a little cold (especially the dining room and kitchen) because we took out two radiators when we changed the kitchen layout. We're considering putting in a floor loop in the kitchen to even things out.
Chris Snyder, WavyGlass.org

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