a little ultra and big domestic load.

Constantin

... put in the right size indirect, then right-size the boiler, is the approach I would take in my climate. Insulating the indirect beyond it's extant insulation is easy to minimize standby losses, upsizing the boiler may not bring as much benefit as you would like. After all, the indirect has to transfer the heat somehow.

If the heat loss is 85K, it'll reach that on 6 days a year. The rest of the time, the house will coast along with a lot lower demand, particularly if all those bodies are running around inside it (think 400BTU at rest 800+ during play per person).

You may also consider installing a few TRVs for rooms that are not always used or where the radiation is too high.

Another consideration is going with a indirect that has a HX with more surface area and better heat transfer, something like a Phase III from triangle tube or the private labeled equivalent that WM sells under the Ultra name.

Lastly, you can use a GFX to pre-heat the incoming hot water with the water going down the drain to stretch the supply of the indirect.

Even with a modulating boiler I wouldn't put in more than 100kBTU, so the 105 Ultra is as far as I'd go. Otherwise, you give up a lot at the lower end for much of the remaining year.

The only time that upsizing rhe boiler to meet the DHW load makes sense is when the DHW load can be expected to be constant and higher than the boiler load. Depends on the climate and the size of the house and the toys in it, I guess.

bob_34

a little ultra and big domestic load

i have a bit of an unusual situation. have at least 10 people moving into and a big apartment- mom dad and 8 kids ages 3-20. old victorian with fhw and large radiators. one zone. 2 full baths, washing machine and dishwasher for domestic. 85,000 btu heat loss. boiler and water heater need replacement.
i would like to use a weil mclain ultra 155 and a super store indirect 60. instead of giving the water heater priority for fear the heat would be off for enough time to be noticeable in the colder months, i am thinking of runing the boiler at 155-160 to keep it in condensing mode and let the water heater sip from that as well. also thinking of switching on the priority and outdoor reset back on in the shoulder months and giving them more fuel savings. will this work? is there a better way ? is a 105 ultra possibly ok?thanks for any of your thoughts.

Unknown

I agree with Constantin

More than likely if you size the boiler by your hot water demand only , you're going to have a way oversized boiler . On bigger homes we've installed indirects that were oversized for the boiler it's connected to . I know the recovery time would be less than if a bigger size boiler were coupled to it , but the storage of the extra gallons of water got the home through peak demand . Worst case , a storage tank can always be added to the indirect .

bob_34

thinking a little more on this, the 85000 is actually the installed radiation load from 100 years ago. with the insulation in the walls and ceiling since then i can run lower radiator temps by probably 30 degrees i suppose. that would give me more capacity to run the domestic simultaneously and squeeze the condensing benefits from the boiler without worrying about the capacity to boot. also- super store used to make a double heat exchanger ss-40-2 about 20 years ago but i haven't noticed it listed currently. by the way -what is a gfx? thanks again.

bob_34

thinking a little more on this, the 85000 is actually the installed radiation load from 100 years ago. with the insulation in the walls and ceiling since then i can run lower radiator temps by probably 30 degrees i suppose. that would give me more capacity to run the domestic simultaneously and squeeze the condensing benefits from the ultra 105 boiler without worrying about the capacity to boot. also- super store used to make a double heat exchanger ss-40-2 about 20 years ago but i haven't noticed it listed currently. by the way -what is a gfx? thanks again.

Guy_6

Check

Check with W/M about the priority function on the control. The ones that I am familiar with will toggle between heat and DHW function on the priority timing. IE 30 mins DHW, then 30 mins heat and so on, until one load is satisfied. If that is the case, you can just work with that function.

bob_34

what a great feature. is this built into the computer control on the ultra or into a separate zoning control sold by w-m?

bob_34

i agree. good advice. a 105 is probably about right.

Guy_6

control

I know that we have it on our Smith GT, and the Munchkin has it as well (on the standard control). In all fairness to Weil McLain, I would imagine that they have it as well, but you should call them just to be sure. Good Stuff.

Tony_23

Size it right...

Do a HEAT LOSS OF THE BUILDING. DON'T size it by connected load. Geeze, you might only need an 80

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Floyd

Ultra parameters...

Bob,
here is a detailed look at the parameters that you can set for the Ultra's

http://www.weil-mclain.com/FTP/Ultra 310/UltraControlInterface.pdf


You can do many things.... I would probably go with t he 105 and back the max. fan speed down for space heating. Then set it so that it would come out of DHW heating after say 30 min., my bet is that it would never stay in DHW heating for that long.....espec. if you let it run to a higher temp. for the DHW load. You can set the temps. for space heating and DHW differently.

Floyd