Residential heat loss & Indirect water heater

Jay_22

I have a home with a heatloss of 105k @ -20f, the boiler is rated at 124k output. When you do a heatloss do you add in the BTU rating of the indirect ? I almost thought that the Super Stor people had said at one time that you didn't need to add it ?

Alan(OnVacationInOregon)Forbes

Correct,

you don't need to add it.

Set up your system for domestic hot water priority where space heating is put on hold when there is a call for domestic hot water production.

Jay_22

Hi Alan,
Thank you for the quick response. This is unfortunatly going to court and I am looking for an answer that I can print that says you don't need to add the extra load of an indirect, I know what you are talking about as I have installed a priority control before to handle this issue. I have never seen in a installation manual, oh, don't forget to add 2 more sections to your boiler. I think we are on the right road though.

Alan(OnVacationInOregon)Forbes

I looked

in some of Dan's books and John Siegenthaler's book, "Modern Hydronic Heating", but couldn't find anything. Maybe someone else has something.

Jay_22

Hi Alan,
I have been on the phone since I posted and I haven't got anything I can print yet either.

Unknown

Call your boiler manufacturer, but honestly, domestic priority control should settle the question. Long and short is that the boiler should never be satisfying the heat load and the DHW load at the same time.

Now if the DHW load is totally huge, that might cause some problems, but otherwise, it's pretty straightforward.

Supply House Rick

I do not believe there is a one-size-fits-all answer to this question. I have Weil McLain boiler and indirect DHW heater, and the heater is on high priority; i.e., heating the house is shut off when DHW heater wants heat; for 30 minutes, anyway. After that, the house gets some time. Now it is summer and I find that it takes only about 5 minutes to satisfy the water heater, and since my heat load for the house in winter calculates out to between 30 and 40 thousand BTU/hr, and the boiler is 80 thousand (input), I would never have a problem.

OTOH, were I running a commercial laundry (hah!), with hot water demands greater than the heating demands, giving exclusive priority to the DHW heater would not work.

Since my main heat load (downstairs) is radiant heating from a slab at grade, I can afford a gap of 1/2 hour once in a while. But in the hypothetical commercial laundry example, I would need to consider the DHW load.

N.B.: this may not help with court case since I am neither an LPE, nor even a heating contractor.

bert

in print

Triangle Tube has something on this in their faq section of their Smart indirects you might find useful.

Charlie from wmass

In some cases the load of the heater is greater than the heat load for the home. this is a time when outdoor reset would be nice but if it is a large indirect and a small home with lots of hotwater use the boiler is sometimes sized for the indirect. Also there are times when the heat loss falls between sizes of boilers availible. so the boiler is rounded up to allow for the what if factors. as long as we do not get carried away like folks have in the past.