Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Indirect water heater question...


I have a question about replacing my old boiler and hot water tank. Our boiler is original to our house (mid 80's) the hot water tank is under 10 years old. We have gotten 2 quotes for an high efficient boiler and indirect water tank. Both are at opposite ends of the spectrum. The first is for a Burham Alpine 105 with 105,000 BTUH input and a SSU45 Superstor and the second is for a Burham Alpine 150 with 150,000 BTUH input and a SSU80 Superstor. My question is do we need an 80gal tank? is 45 to little? We have gas heat. 4 zones. Our house is about 2500sqft with 3 1/2 baths. We have not done a heat loss yet. Do you have any thoughts? Our old system is an old Burnham boiler with a 40 gal tank. We have 2 adults and an infant presently living in the house.




  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I am just a homeowner.

    "105,000 BTUH input  150,000 BTUH input"

    Did both of those contractors do a heat loss calculation? I am surprised they are so far apart. Or did one just pace around two sides of your house and the other look at the nameplate on the burner of your existing boiler? You say you have not done a heat loss yet. You cannot possibly decide on a boiler until a heat loss is done. I do not see how the contractors could propose boilers without knowing the heat they must supply. Especially with a mod-con, you do not want an oversized boiler.

    Similarly, you will need to know how much hot water you need. For my mod-con with indirect, I calculated that a 30 gallon indirect would be enough: I live alone and am not a teenage girl who takes frequent long showers. I generally use cold or warm water in the washing machine. My shower has a low flow head. I got the 40 gallon sized indirect and I have never run out of hot water. My boiler manufacturer has a little calculator worksheet to calculate the size you need. I imagine it would work as well for any manufacturer. There may be a better way to size an indirect.

  • Zman
    Zman Member Posts: 7,572
    What do you have?

    What kind of water heater do you have now? It should have a BTU input rating and the gallons it stores. Does it keep up?

    What size is your Boiler? It should have a BTU input plate on it. What area of the country are you in? Do you have hot water baseboard heaters?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Halfbreed
    Halfbreed Member Posts: 4
    Water heater sizing

    General practice is to match the size of your tub to the water heater capacity. If you have 1 or 2 full baths with a tub and it holds 60 gals, install a 60 gal water heater. If you have 3 full baths, two normal baths, and the third with a 100 gal capacity tub and a shower with 2 high volume shower valves, 5 body sprays, 2 large volumn shower heads, you may want to consider either a larger than 100 gal water heater or 2 water heaters piped in perfect parrelle. Match the water heater output with the demand. Most manufacturers have a customer help line and can help you with this. Keep in mind that in Massachusetts we have to size our water piping figuring a residential load at 50% of total fixture units. Not all of the faucets will be drawing water at the same time.Below is another style of Indirect Water Heater.I use an external plate exchanger and a storage tank, like an electric water heater, instead of an indirect with a coil inside. It overall is cheaper in materials and more efficient. If there is a problem with an indirect with a coil inside, as in a tank leaking or the coil leaking inside the tank, it is costly for the customer to have the whole thing replaced. With the plate exchange and storage tank method, if the tank springs a leak, then you are only replacing an inexpensive electric water heater. If the plate exchanger has a problem, then if you use a type that is installed with unions, you disconnect it and replace it with either a new one or a refurbished one and it is still much cheaper than using an indirect with a coil inside. Whatever you use as a storage tank you will need 3 ports to do so. With an electric water heater, the drain port on the bottom is where you will send the cold water supply to the tank and a tee off of that to feed the plate exchanger. The cold port on the top is where the heated water from the domestic side of the plate exchange will dump into. Either remove the elements and plug off with brass plugs or disconnect the wires and remove and bypass the top thermostat. Use the lower thermostat to control the temperature of the tank. You can remove the top or bottom element and bushing it down to install a well for an aquastat or a sensor to control the temperature instead. It is basically an Energy Kinetics' System 2000 design. I use it in all of my heating systems, hydronic or steam, for domestic hot water. As I stated, it is a couple of hundred dollars cheaper overall and saves time and money if service is needed, and is also a little more efficient. Keep in mind that if the boiler takes more than 5 minutes to reach 120 degrees from a cold start, then you will need to install an aquastat to delay the domestic circulator from coming on right away and prematurely cooling down the water in the storage tank before the boiler produces hot water. Reply Edit
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Heat loss needs done before installing boiler

    since few people are willing to pay for a heat loss before they get their boiler we include it in our quote. Sizing of boilers is an exact science but the price between sizes is not always that great if a rough heat loss is done when the contractor looks over the system. Water heater sizing is based on fixture loads with common sense to what actual and potential usage is going to be. Also a smaller heater with a higher temp to keep down bacteria growth then going to a mixing valve is what I prefer to use. There was a time I would install large heaters and run low temps with no mixing valve but we live and learn. 
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
This discussion has been closed.