Boiler recs for radiant/hydronic BB retrofit

Reyesuela

Ok, here's my situation:

I need a boiler for a mixed radiant and hydronic BB retrofit. I want it to be the right kind for my application, and I want it to run as cheaply as possible! Initial cost isn't as critical because we're going to be in the house a l-o-n-g time.

I'm going to have an indirect water heater attached, which means that the boiler will be coming on summer and winter. We have a 6 month heating season here. The indirect water heater will have a rating of 150-160 gallons, which, depending upon the brand, translates to a 40-80 gallon tank.

The boiler will start out servicing the house with a mixture of radiant and baseboard hydronic, and I will eventually switch over to radiant only.

In addition, I'd LIKE to oversize (I know, I know) the system in anticipation of an addition that will let me add our guesthouse to the system. The main house as it is now has a heatload of 36k btu/h. With everything else, that would rise to 70k btu/h.

To further complicate matters, during the day, my heating needs are MAYBE a fourth of what they are at night (max night figures above) because our house has passive solar. On sunny days in the winter, the upstairs is 40-65 degrees warmer than the outside temperatures--no heating needed at all!

I was thinking about a modulating system, but those only exist in propane and natural gas-fired models. Natural gas isn't available here. Oil, once BTU is taken into account, is between 1/2 to 2/3rds the price of propane here.

So I want the solution that's the cheapest--oil--but that is also easy on the equipment! I'm afraid that if I get a traditional boiler, the highly variable heating requirements will cause a boiler sized to take care of our max needs to short cycle most of the time and will shorten its life. Or will having the indirect hot water tank be enough of a load that it will take care of that potential problem?

Thanks so much!

Unknown

Hi Efficiency FCX Condensing Oil Boiler

Check out the Monitor FCX condensing oil boiler. It's exactly what you're looking for. 76,000 BTU output. Longstanding track record for relyability. 95% efficient. Good group of people to work with too. Tell them Gary sent you;-) http://www.mzboiler.com/products/fcx/index.html

You may concider running the floor loops on constant circulation to redistribute the solar gain through the entire home. This will also help on short cycling.

Gary

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Joe_13

No oil boiler @ 34K

Usually 70-90K BTU is the smallest. 80 gal indirect will need over 120K BTU to recover in a resonable amount of time. Get a 50-60 gal. Many people doing radiant need a buffer tank to stop short cycling on bigger boilers. Burner will run longer (good) and cycle less often (save oil) as the radiant will suck BTU's out of the insulated tank. Look up indirect tanks like TurboMax, ErgoMax, Dinkirk Artesian. Use the indirect as a buffer tank for a low mass boiler /radiant system as it will hold about 20 gal of hot boiler water and let the domestic water run through a copper heat exchanger in the tank. Let the boiler cold start and it will just service the tank in summer for hot water.

Reyesuela

Thanks!

Thanks for your help! I'm writing Monitor now. *g*

Reyesuela

Those were just my heat load calcs for the house. They didn't include the water heater needs! I knew I'd need more for the hot water.

It looks like with most brands' water heater ratings that I can replace my two fifty gallon HW heaters with just one 40 gallon indirect tank! NICE.

Checking what you're saying--you're suggesting that I should run my domestic hot water and the radiant out of the same tank instead of having some water go to the tank and some directly to the radiant system?

Joe_13

Inverse indirects

Most indirects just have a heat exchanger coil thats filled with boiler water. Usually around 7 gal of boiler water in the coil. Inverse indirect fills the tank with boiler water: 20-26 gal and the domestic water goes through the coil, like a boiler with a tankless coil. Puts the water mass in an insulated tank rather then leave it in the boiler which has high stand by loss as the heat goes up the chimney.

Steve Eayrs

I would consider..........

the following in choosing the boiler;

- controls make a big difference. The boiler is just thh biggest component in the system, and can only operate efficiently if controled and piped right.

- The size of the boiler does not have to be the combined load of dhw and heat loss. Pick the largest load of the two, (most likely dhw in your case), and size if for that. The dhw can run on priority. (Tekmar makes great controls!)

- The overall cost of operation should include some idea of maintiance costs. You will have higher costs to mantain a condensating oil-fired boiler (needs cleaned more often, flue gasses very corrosive, etc.) than with a more standard but high eff. boiler. I would say the life span of such boilers, is shorter too.

- Again controls....your boiler is only going to operate at their advertized eff. if the controls can help it do it.
In my opinion the monitor does not have the best controls, to keep it operating where they say it can. If you want a thought out packaged system, I would go with something like the Veissmann which has a great control statagy as part of the package.

- Also I don't see any need for buffering tanks on large mass boilers. Such tanks are usually the weakest link in the system, and may need replacement before other components. They also often take up too much floor space.


Steve