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Downrating a boiler -is it a good idea?

Hello all,
I'm new to the forum and have a question about downrating a boiler.
Currenty, I have an old (1940's?) American Standard boiler for the gravity hot water system. A couple of contractors have suggested energy efficient new boilers in the $7k-$8k range. One heating contractor suggested downrating the 300btu boiler to 100k-150k by reducing the size of the burner openings,installing sensor to monitor outdoor temp. and adding something to the water to make it more efficient (slippery?).
Is this a sensible alternative to spending $8k. I believe I can downrate the boiler myself with the help of a local supply house. I would skip the other ideas for the moment. The house has been insulated recently so the 300,000 btu rating is wasteful according to the heating specialists. My heating bills seem to confirm this.

Any suggestions would be appreciated.

Re: Downrating a boiler -is it a good idea?

I have never heard of down rating a boiler but the part about adding something to the water to make it more slippery sounds a bit scary. You would have to be sure there was absolutely no way that any water from the boiler got into the water for the rest of your house.

Re: Downrating a boiler -is it a good idea?

Thank you for your concern but this is a closed sysem. There is no way water from the heating system would enter the regular water supply.

Re: Downrating a boiler -is it a good idea?

A heating system THAT old is considered way out of date, probably wasting half the fuel consumed, which goes right up the chimney because a system that old can't utilize the heat produced by the burning fuel.

In most cases such a system should be completely updated just in view of today's fuel costs.

If nat. gas is not an option, & depending on your location & building sq. footage, you should be burning no more than 600-800 gallons of oil/yr.

Major changes in boiler efficiency & piping in recent years enable modern boilers to burn 85%-95% of the fuel they use---you would see a dramatic drop in fuel oil usage---I would estimate from 30% to 50%.

Not only the boiler, but the piping distribution system on a gravity system often has to be replaced to cut down on the amount of water that is heated & distributed in the old piping--a gravity system & old boiler may have 50-100 gal of water to heat & distribute, where today 15-20 gal of water is used, if not less.

Perhaps the radiators should be saved, but everything else usually has to go--3/4" PEX piping is snaked thru the walls & connected to the rads or installed baseboard, or even under floor radiant.

Even a basic run-of-the-mill boiler = $1500 + an indirect hot water heater ($700), install costs for piping & boiler ($2000) = $4200 as a base price---get more estimates if $8k seems to high.

Downrating the boiler & working with the system you have would be stop-gap, but would only cost ~$200 to change burner nozzle size, clean the system, adjust fuel pump pressure, combustion analysis of flame.

Propylene glycol (antifreeze) is often added to boiler water, but I would advise against it as an unnecessary expense.

Could you advise of the sq. footage to be heated (including boiler room) and the annual # of gallons or oil used.


Re: Downrating a boiler -is it a good idea?

Oh my. A year has gone by since I checked this site and I have yet taken any steps. In answer to your question, the house is about 2600 SF. A 3 story house with semi-finished basement of about 1000 SF?
As I mentioned, the current hot water boiler system is rated at 300,000 btu. Heating specialists have measured the house and radiators and have suggested a new boiler in the 100,000 to 125,000 range. An old timer suggested the downrating- reduce the burner aurifices, replace the gas valve, add a damper, and install some monitoring system that checks the outside temp.
The boiler itself seems solid. A roughly 4'x4'x4' box. As he explained it, since the house has been insulated (there was nothing in the walls or attic floor prior to 10 yrs ago), the 300,000 is overkill.
In my mind, this whole idea seems logical. While I know that the new systems are more efficient, it seems that this one could be made to perform a lot better. So much of the burner heat is going up the chimney whereas if the burner was lowered to 100,000-150,000 btu and cycled on more often, less heat would be lost up the chimney.
And yes, the substance the heating specialist was suggesting to add probably was antifreeze but I don't fully understand how that would improve anything.
I would appreciate your comments.

Re: Downrating a boiler -is it a good idea?


Yes, I would still tend to favor you going with a new boiler instead of trying to update the old one--sorry, I didn't realize it was a gas-fired system---but I would like to hear the amount of the quotes you got, both for a new boiler, and an update of the old system.

If an update of the old system will cost considerably less, it might be a better option---it would be a long, drawn-out job to do a complete overhaul during the height of the heating season, so it might be best to wait until spring until this is done.

Another issue in my mind is would they be able to use the in-place pipes and radiators, or would they have to rip EVERYTHING out???

Yes, 125,000 btu/hour for the size of the new boiler seems about right (simply based on the square footage), but it's always best to do a HEAT LOSS CALCULATION to get an accurate sizing of the new heating equipment so you don't waste any fuel running a too-big boiler.

Please advise if you have any dollar amounts for some of the quotes you have received & what it includes.

Re: Downrating a boiler -is it a good idea?

For boiler efficiency a new 125000btu boiler is going to be much more efficient then downgrading an existing one, though if you could accomplish the task yourself at minimal cost then it would be a decent stop gap measure.

For an additive, it might be similar to a 'water wetter' that is used in automobile cooling systems sometimes. It allows the water to transfer heat more effectively by preventing surface tension in the water. In automobile applications it typically reduces coolant temperatures by around 10 degrees F. In the case of a radiant heating system it would likely promote better heat transfer from the working fluid through the radiator itself and also improve heat capture from the boiler to the working fluid. That said, I'd never heard of something like that used, but I could certainly see how it could work. I would NOT suggest just dumping automotive water wetter in to your radiant cooling system without asking around first. It should be safe, but it might be totally different from the product that is being suggested and it might not work in copper piping (it is typically designed for aluminum, cast iron and brass materials which is what is used in automotive radiators and engine block cooling passages).

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