Correct Boiler Sizing

Pat_12

The heat loss calculations performed for my current job call for a total heat loss of 56,000 BTU's (excluding water heater). I would like to install a Peerless Pinnacle 80m with an indirect fired water heater. The boiler has a net IBR rating of 64,000 BTU and a DOE rating of 72,000 BTU's. My goal is to design a system that is efficient as possible without going overboard. As such, I have not figured in any requirements for the indirect fired water heater. The heater will be given priority in the system. The distributor is reccomending that I install the 140M, a boiler with a net IBR rating of 112,000 BTU and a DOE rating of 129,000 BTU's, as this will give me more than enough heating capacity to both heat the home and hot water simultaneously. As the Pinnacle is a modulating boiler, the distributor believes that the system will still be efficient, and provide a lot of excess heating capacity. My concern is that this excess capacity will be costing the customer more up front and will generate higher operating costs over the life of the system. I also do not want to install a boiler that is too small. Let me know your thoughts on how much "cushion" is safe to build into your jobs.

Pat_12

Correct boiler sizing ?

The heat loss calculations performed for my current job call for a total heat loss of 56,000 BTU's (excluding water heater). I would like to install a Peerless Pinnacle 80m with an indirect fired water heater. The boiler has a net IBR rating of 64,000 BTU and a DOE rating of 72,000 BTU's. My goal is to design a system that is efficient as possible without going overboard. As such, I have not figured in any requirements for the indirect fired water heater. The heater will be given priority in the system. The distributor is reccomending that I install the 140M, a boiler with a net IBR rating of 112,000 BTU and a DOE rating of 129,000 BTU's, as this will give me more than enough heating capacity to both heat the home and hot water simultaneously. As the Pinnacle is a modulating boiler, the distributor believes that the system will still be efficient, and provide a lot of excess heating capacity. My concern is that this excess capacity will be costing the customer more up front and will generate higher operating costs over the life of the system. I also do not want to install a boiler that is too small. Let me know your thoughts on how much "cushion" is safe to build into your jobs.

Joe_13

Check recovery rate of indirect

It's all gonna depend on how much hot water you want to use.
Your indirect will have a calc sheet to figure out your hot water load requirement. There's also a spec chart on gpm of hot water @140 and @115. Most usually look for 100K BTU min. The 140 will modulate down to 43K BTU's, sounds perfect. The day you run a load of wash and 2 people can't take a shower at the same time, you'll be mad you didn't get the 140.

Radiant Wizard

Distributor is Oversizing the Boiler

The boiler your distributor is sizing is oversized. They are giving you a boiler that is twice the size for the job. The boiler that you choose is right for the job. The indirect has no bearing unless you have this enourmous demand for hot water and from the heat loss I would say that you have a 2,500 sqft or less home, 1 1/2 bath, 1 full bath and a Master bath with a whirlpool.

Now just guessing I would say your boiler is pretty close to 100,000 gross btus. Here are some ratings for a Crown Mega-Stor (I believe this is also Peerless' "Partner Series Indirect but I could be wrong).

MS40 40 Gallon/132 Gallons First Hour Rating at 140 degrees

MS53 53 Gallon/140 Gallons First Hour Rating at 140 degrees.

The boiler you sized along with one of the indirects above are more than adequate for the above job.

lisa

I agree with radiant wizard

don't oversize!!

Unknown

Think it was Dan that said...

The desire to oversize boilers regularly exceeds the male sex drive.

It's a modulating boiler. One size fits all as long as you are not undersized it's my understanding that no efficiency is lost. (I could be wrong)I'm interested if the other guys here agree.

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Floyd_5

The point here.....

is that the total loss was only 56,000, the turn down on the 140 only goes to 43,000, so most of the time that boiler would be well oversized......the 56K is probably high and a worst case deal.... and.... most of the winter the load will be 50% or less of the 56K.... the 140 will be turning back as far as it can go and then will be short cycling......so go with the smaller boiler.... it will still give you plenty of hot water, unless you are going to install one of those "car wash showers" or have a huge whirlpool tub.... if you need more hot water go with an 80 gal indirect and not the bigger boiler.

Joe_13

It's not close to 100K, the 80 max's out at 74K BTU. The MS-40 lists a 120K gross boiler (I'd guess 100K net BTU) to get 166 gal/hr @ 140 degrees(@200 degree boiler water which I don't think you want to run on the munchkin/pinnacle) that's only 2.8GPM. A peerless 40 gal indirect will only give you 130 gal/hr (2.1 GPM) with 80K BTU. I'm not saying it won't work, I'd just make sure my wife took the first shower so I'd won't hear the complaints.