WM Ultra Sizing

Tony_23

Should be for current conditions. Any improvements are gravy.

My advice is to tighten the structure FIRST. Keep the heat in.

It's just like money, what you keep is what's important, how you make it is secondary.

Eric_21

WM Ultra Sizing

I have done the heat loss calculations for my house and came up with a loss of 75,000 BTUH. I want to have a WM Ultra installed to replace my old system. I will also have a 40 gallon indirect installed at the same time to replace the current 40 gallon direct fired water heater which pretty much keeps up with our load. If I add 20% to the 75,000 that gives a total of 90,000 to allow for some extra. My question is: would the Ultra-105 provide enough output for the heating and indirect? With the NET I=B=R rating of 81,000 (for the 105) I would assume that the safest bet would be to go with the Ultra-155?? I just want to be sure I get the right model recommended for my application.

Thanks.

Floyd_15

Ultra 80 would do fine.....

If your heat loss is correct than you will have all the poop you need from the 80.
More important is the indirect that you use and the way that it is piped..... don't put a big V-8 in a VW Bug...... make sure that you get an indirect that has low hwad through it and than pipe it according to the directions. The 80 with a plus 40 will give you all the hot water that most normal people can use. If you want you could go to the 105 and back down the heating side of the Ultra to 80,000. The 155 is really over kill and won't mod. down enough in mild weather.... don't go there.....

Floyd

Tony_23

The 80

should be plenty. Absolutely no more than 105. IBR doesn't mean much if your set up right for an Ultra. The pick-up factor needn't be considered as the system never gets completely cold.

hr

radiant or HW baseboard?

My suggestion would be the 105. You won't hit that highest efficiency number if you need to run over 140 some of the time. Those high efficiency numbers are calculated with a 110° supply and a 90° return, as noted in the Weil brochure.

With a modulating burner a small oversize will not be a big deal. The 105 will mod down to 21K on low fire. It also leaves some expansion room for an addition or shop in the future.

hot rod

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Eric_21

I have a 55 year old two story colonial that has cast iron radiators. I assume this is a "higher" temp demand (>140) but would also give a greater differential than regular baseboard, so better efficiency??

I have no room to expand this house so what I have space wise is all that I have. We also have original single pane windows in this house so the heat loss will only improve in the future if I add new windows. What I'm getting at is if the Ulta-80 will handle the job as my house is now then for the future the 80 appears to be the best choice??

Thanks for all you help. Eric

Eric_21

hot rod . . . Tony . . .

I won't be able to tighten my structure first. I have a crack in my current cast iron Crown boiler. So I will have to install the new boiler first then work on the structure. I just want to be sure that what is recommended or installed is not over kill or under kill for that matter. If the Ultra-80 will handle the job then I don't want to have a larger one put in if I don't have to????

hot rod: Based on my system (above) would you still recommend the 105. I am leaning toward the 105 to allow for a little more "squeaking" room.

Thanks for all the great advice.
Thanks.

hr

My question

would be how accurate you feel you first heat loss calcs are. If you think you hit it well, THEN added 20% you are probably going a bit overboard with the larger size. I believe the heat load calcs all have a bit of fudge and over size built into them. With your added 20% you could be 30% or more over the actual load.

On the flip side the next size up generally only adds a couple hunderd dollars and it will still modulate to your load.

What about venting? Long vent lengths will cut into the boilers output a bit.

Pretty close to call on this one, you would have more of the facts to base your decesion on.

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Bob Sweet

hr, could you explain the reason why

a longer vent would cut into the boiler output? Thanks

hr

By longer

I mean exceeding the tables in the manual. This can happen with actual pipe distance, or a lot of elbows. In the Weil manual 90° ells cost you 7 feet of pipe run.

Short turn ells cost you a whopping 16' per fitting

I believe the HTP folks have derate figures for excessive lengths in their Munchkins, as well as a table for using smaller diameter that listed.

Some contractors are replacing old Hydropulse systems with Munchkins and using the exisiting 2" PVC vent pipe. It, with factory approval, can be done but cuts down the actual boiler output.

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Tony_23

80

I'd stick with an 80.

You're also going to reduce your infiltration a bit by going from a burner that uses room air to a sealed combustion appliance. That'll give you even more cushion.

The vent length "shouldn't" be much problem. They allow 100 ft. of pipe on each w/two long radius 90's included. All other ells are a deduction that a little planning will overcome.

Go for it and don't look back ! You won't be sorry !

Eric_21

Thanks!!

Thanks for all the great advice. I feel I am a much better educated consumer now!

I am fairly confident with my heat loss calculation. I got HVAC calc and it pretty much matched up with the Slant fin calculation.

The length of the vent should not be an issue. I will either send it out the side block/ brick wall or send it up my 30 ft chimney. Worst case would be four 90's, but more likely three.

I will double check my heat loss calculations and then make my final decision. Not sure exactly which model WM-Ultra I will end up with, but either way I know at this point that I will be getting a great product!

Thanks again.

Eric