Steam to Water Conversion

Converting Steam Systems to Hot Water Systems

Are you are thinking of converting an old steam system to a hot water system. Many steam systems are very inefficient due to lack of maintenance through the years and an old oversized inefficient boiler. It can be very costly to convert a steam system to a hot water system and may create some issues. There have also been many steam systems converted with no problems. We must ask ourselves these questions.
Why do you want to convert it?
Is it worth the investment to convert it?
Should I just improve the existing steam system?
It has been estimated that by converting from an old steam system to a higher efficient hot water system could save you between 15% and 60%. They usually average this around 35%. I personally think this should be closer to the high side with the products on the market today. That is of course, if the new boiler is properly sized and properly piped. This is a good system for the newer boilers running in the mid to high 90% range. This is a more expensive boiler which requires more maintenance but is an excellent choice for this type of application. The mod/con boilers are more efficient when cooler water returns to the boiler. The steam to water conversions usually operate at a greatly reduced water temperature. The installation costs vary dependent on where you are located and what needs done for the conversion.
Is there a pay back or breakeven point at these costs? You need to decide that for yourself. How long are you going to live there? How high are your fuel bills? What can be done to update your current system and at what cost to savings ratio. Look at the cost and the fuel usage. Calculate a savings and look at pay back.
We will look at this from a few angles. The first will be what to look for in a steam system before thinking too hard about converting it, how to size the new hot water boiler, what we need to do before we convert to hot water, and how to convert it.

Surveying the System Systems

1. Look at the radiators first. If you look at the bottom of the radiators you will see all the vertical sections are connected (touching) at the bottom. Are they the same at the top? If not, you may want to avoid this conversion because these are steam only radiators.
2. Do the radiators have one or two pipes connected to them? In only one you will pay more for all the return piping to be installed and run back to the new hot water boiler.
3. Do a room by room heat loss for the building . A heat loss will give you the heat lost per room and a total building loss to properly size the boiler. Check the heat output for each room radiator and compare it to the radiator output. You more than likely will but you need to do this step to verify the radiation can heat the room.
Steam radiators heated with steam put out 240 Btu's per square foot of radiation. When heating with hot water the radiation will only put out 150 Btu's per square foot of radiation. Do the heat loss and measure the radiation. Divide the heat loss by 150 and the answer should be equal to or less than the radiator square foot in that room.
A heat loss for a room is 6200 btu's. The radiator is equal to 45 square foot.
6200/150=41.3 sq. ft. this room will heat fine. If the radiator would have been less than 41 sq. ft. it would have been a problem.
Size the new boiler per the heat loss not the radiation. If you size the boiler off the radiation you will put in a bigger boiler than needed and it will short cycle costing you more in fuel and maintenance.
4.Do not get rid of the cast iron radiation! Cast iron radiation has a big percentage of heat output is radiant heat. Radiant heat does not create air currents. Air currents increase heat loss. This is not a huge difference, but every little bit of savings helps. Cast iron radiation produces less drafts than any other heat including copper tube aluminum baseboard. Radiant in-floor heat is the only heat style that is better than cast iron radiators. The cast iron radiators will create a more comfortable home utilizing less fuel.

2. What to do before we start?

1.First run the steam pressure up to 10 psi and check for leaks. I usually do this with a flashlight as it will reflect off the steam. Some people use a mirror to see if it steams up.
2. If there are return lines on the radiators are they big enough to carry the water back to the boiler?
3. Determine if you have wet or dry returns. If you have wet returns plan to replace them or at least about the first 10+ feet from th boiler. They have collected a lot of dirt through the years.
4. If using the same boiler due to not being very old verify with the manufacturer if it can be converted to water and do they offer a conversion control kit.
5. Determine the water pressure you will need to be operating at. 
6. How many zones you want. Is it doable? Be careful here. Many times, the mistake made here is over zoning and causing the boiler to short cycle.

3. How to Convert your system

1. Pay special attention to piping. I suggest the use of primary/secondary piping at the boiler or the use of a buffer tank. There will be too much water in the system for all the water to flow through the boiler to maintain good delta-T through the boiler.
Size your circulator to the heat loss of the system is doing a single zone. If doing multiple zones, size the zone circulators for the heat loss.
4.Size the expansion tank according to water volume and water temperature rise. Do not use the manufacture's charts for these installations. The charts do not work well with steam to water conversions and gravity hot water installations.
You can determine the system piping water volume here, add in the radiation, than add the boiler water volume to the total gallons of the system.
5. Set the heating curve to match the system load as compared to the heat loss.

4. Boiler information, piping andf what to expect upon completion

1. Choose the boiler design of choice. You can use a cast iron boiler of 95%+ high efficiency boiler. If this is a larger system, you may consider multiple boilers. It is very important if leaving any old iron pipes install a magnetic strainer on the return side of the boiler(s) to protect the boilers and circulators.
2. Good even heat throughout zones or entire system. Make sure the thermostat cycle rate per hour is set to gravity hot water or steam. One may be better than the other depending on the amount of the radiation in your system.
3. Noise free operation. There should be no expansion noises. The steam to water system should always have an outdoor reset control installed to maximize the comfort and produce the lowest fuel bills.
4 Little, if any pressure fluctuation on the pressure gauge.
5. Increased comfort levels
6. Substantial fuel savings.

We have a seminar for more in depth information that you can view for a small fee.Please contact us to view it or have me do it for your group.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property or bodily injury from applied information found on this website as it should be reviewed by a professional.