indirect & boiler sizing

[Deleted User]

Scott

I would look around for a few other reps. You should/need to have heat loss calculations done for sizing the correct size boiler to heat the house. Especially today with the prices of fuel oil/gas & electricity. Installing the same size boiler or bigger your going to use more fuel along with the boiler short cycling. As far as indirect water heater, it is treated as a separate zone and set up as a priority zone with a TEKMAR or TACO controls. The indirect should not be added into the calcution for heat. My house we moved into a year ago, it is 1800 sqft, 38 yrs old colonial. The old boiler is a 15 yr old gas, 144,000 btu. I done a heat loss calculation using Weil Mclains site also Slantfin, total heatloss is 58,700Btu's. I installed a new Weil Mclain Ultra 105 boiler which I adjusted it down to 63,000 btu's to heat 2 zones of baseboard. When the indirect water heater calls for heat, the zones shut off until the indirect water heat is satisfied, then switches back to the zone calling for heat. When my boiler is heating the indirect, it is at max fire of 105,000Btu's as compared to my old gas water heater which was on 56,000Btu's. My indirect water heater is an Weil Mclain Gold Plus forty. With four people talking showers, one after another and running the dish washer or washer machine, I have endless amount of hot water. I couldn't do that with the old water heater. I hope the info is helpfull. Here's a couple of web site for heat loss calculation:

http://www.weil-mclain.com/contractor/images/BoilerReplacementGuide.pdf

http://www.slantfin.com/pdf/heatloss_calc_form.pdf

david_22

indirect & boiler sizing

I'm trying to choose between quotes to replace my homes heating & DHW system. I have had reps from 3 business come to the house for estimates and none have made any effort to determine what the actual heat loss of my home is. I'm concerned that some (all?) may be recommending oversized boilers. The home is about 80yrs old and 2500sq ft. I'm looking for an oil fired boiler that will serve 1 zone which is forced hot water, 1 zone which is forced hot air and 1 indirect tank for DHW. The estimate for the smallest boiler is a Dunkirk Ultimate 138000 btu output coupled with a 45 gallon super-stor. On the high side one guy suggested a 170000 btu output Buderus with a 53 gallon crown mega-stor. When I indicated I thought 170000 btu sounded high for a home my size the rep said that size was necessary to accomadate the needs of both the heat (based on boiler & furnace output currently in house) and the indirect. What I was hoping is that the pros out there could comment whether these proposed boiler sizes sound outragous and how much the indirect tank should factor into sizing the boiler.

Constantin

Hmmmmm

I'm just a mere homeowner myself, but the quotes do sound high and I wonder to what extent I would trust any "professional" that claims a heat loss calculation is optional as opposed to mandatory. Have you tried to "Find a Professional" using the link above?

I have enclosed a small excercise in incomplete Excel programming that I have yet to update for all the good suggestions the fine professionals here have made. However, it will give you a ballpark as to where your current heating needs are, based on last years consumption.

The only data you need is the gallons of oil consumed, your heating degree-days for last year (wunderground.com has that data), and a bit of time to waste.

Unless you house is a leaky glass-palace built with single-pane windows, I doubt that your heating loss will be much above 40BTU/ft² on a design day (the coldest day of the year). Thus, a 100kBTU boiler is likely to be the biggest size you'll ever need. However, many people in homes like yours that have retrofit insulation, good windows, etc. enjoy heat losses as low as 15-20BTU/ft², even in cold climates.

Given that most US gas water heaters have nowhere near a true 50kBTU output rating, I doubt that a smaller boiler will be a problem. In fact, you can always upsize the indirect water heater a bit in case you have a large dump load (like a jacuzzi, car-wash shower-heads, multiple bathrooms, etc.) Upsizing an indirect tank can be downright inexpensive compared to grossly-oversizing the heating system.

As for what brand to chose, I'd go with the brand that a good, qualified installer is most familiar with, as there are many small boilers that do a great job of providing reliable heat. Someone has to maintain the system too, so I'd factor that in as well.