boiler size for indirect and mixing valve

Jake2010

I have sent a previous post but had trouble connecting to it with my new question.

I am replacing my oil boiler, heat loss is supposedly 50,000, 118 feet of base board, 2,000 sq ft house, all new high quality windows, two adults, three children.  I presently have a weil mclean 40 gallon indirect.  I would like to go with either MPO 84, or 115 if needed, or Buderus g115ws/3 section.  I am still concerned about meeting the hot water requirements. I don't really want to go bigger, will the boilers mentioned be sufficient? Contractors have told me to go bigger. 

I have heard about utilizing a mixing valve on the indirect to have more hot water capability.  Does this effect efficiency of boiler as it will be heating up water at a higher temp?  Just an average homeowner trying to make sure I get this done correctly.  Any thoughts or advice are greatly appreciated.

kcopp

size the boiler ....

to your heat load. DONT add extra boiler size for the indirect. If you have concerns go w/ the next size of indirect up. example. I have a Buderus 115-21 (3 section) I have a 60 gallon Super stor and do have a mix valve. I set the tank for 140 then mx down to 125. I have never run out of hot water. I do prioritize the indirect w/ a tekmar 260. If you up size the boiler you will just be wasting fuel.

Jake2010

I already have 40 gallon indirect

I already have the indirect which is 40 gallons, which I would plan on setting up on priority.  Do you think the 40 gallon is big enough for a family of five?  How do you like the Tekmar 260? Do you use it for outdoor reset also?

CMadatMe

Demand

How many showers in the house? What's in them, ie any human car washes or whirlpools? How many taking a shower at the same time?

Jake2010

No human car washes

just 2 showers, no plans for any whirlpools.  We actually have not tried to take two showers at a time with the present set up.  Maybe down the road when kids are older and we are all getting ready for work and school at same time. We generally are doing three in a row right now in the morning with no problems, one bath and a shower at night, but that is with an old oversized boiler. I think the hot water supply lines are also just 1/2 inch if that helps at all. 

CMadatMe

Agree

With the others bring up the temp and mix down. Sounds like you have a few years until the water gods get older. Put your pennies away and replace it down the road if need be.

Jake2010

Are saying

to replace the boiler or indirect down the road. 

CMadatMe

Indirect

Add the indirect down the road.

Jake2010

The one

I have is 7 or 8 years old, what is the general life expectency for an indirect? 

kcopp

funny thing about.....

having more hot water.... the kids stay in the shower longer!

Jake2010

I generally

don't let them take long showers, try not to anyways, I'm all about turning the water off if I need to.  However, when My daughters are teenagers they are likely to be a little more frightening.  All kidding aside, I would like to get the best scenario for the next several years.

SWEI

indirect sizing and selection

Make sure you size your indirect based on first hour and continuous delivery.  If you pick a quality indirect having the same gallon capacity as the old tank heater, you're going to spend more on the indirect and could have several times the capacity you actually need.

Jake2010

At this time I am

trying to size a new boiler to the 40 gallon weil mclean indirect that I presently have.

Jean-David Beyer

size a new boiler to the 40 gallon weil mclean indirect that I presently have

If you have the I&M manual for W-M's Plus Line Indirect water heaters, Table 3 on page 29 is a guide. I am driving my Plus 40 heater with an Ultra 3 80K BTU/hr mod-con. It easily handles my hot water load, and usually recovers in about 10 minutes. I even run the supply at 175F instead of the default 190F. I have no teenage daughters. ;-)



Now if you do not want to run a W-M Ultra boiler, you could, I imagine, run another boiler of similar ratings. These assume the indirect gets priority if there are competing demands for heat (such as heating the house).

Jason_13

MPO-IQ

With the heat loss of 50k use the MPO-IQ which will automatically prioritize the indirect and also wire the pump right into the boiler, also offers a pump pre-purge. If you are using a multi-zone relay you don't need to include the indirect in the relay so you can get a relay panel with one less zone and no priority. The boiler already handles 2 pumps. Can also use the odr cards which will also prioritize the indirect and still wire the indirect pump to the boiler.

Jake2010

Are you recommending

the MPO 84, what is the pump pre-purge that you mentioned, could you explain.

Jake2010

Appropriate temperature for increasing indirect capacity

If I am going to go with a boiler which is sized to my heat loss, what is  good target temperature for the indirect HW to increase capacity when using a mixing valve? I have read that you can somewhat increase capacity to about 60 gallons.

The logomatic 2107 has a indirect temp max of 140deg.  Should I use a different controller for my purpose?