Need help in sizing Lochinvar Boiler

Val_LI

I'm in a middle of remodeling project.

My house is 3200 sq ft. Spray foam insulated, brand new windows.

First floor is getting radiant heat - 1050 sq ft.

3 bathrooms upstairs (about 350 sq ft) are also getting radiant heat.

Middle (living room ) and second floors are getting hydronic forsed air from 2 coils (one in attic, the other one in a garage).

I'm planning to install wall mount Lochinvar Knight unit with Lochinvar 80Gal indirect water heater and set it up in 4 heating zones with 5th zone for domestic water.

Plumbers I spoke to tend to throw large numbers at me...between 150,000 and 175,000BTU.

I have a feeling that WHN-110 (110,000 BTU input; 89,000 BTU output) will be just right.

Could someone help me to get correct boiler size? Am I wrong? Am I right?

Your help will be greatly appreciated!

JStar

Heat

Any contractor giving you a size, without doing a heat loss, is giving you a wild guess. Has anybody done a proper Manual J heat loss?

Val_LI

Val_LI

Nobody has done that yet. The biggest effort I've seen so far was applying the rule of thumb..35

Zman

Design

It sounds like you are getting ready to install a great system.

I would pay to get the help of a good designer. Not only does a heat loss need to be done, some careful attention needs to be given to the sizing of the air units as well as the rest of the system. Find yourself a good design professional and rest easy. Many supply houses and manufactures will help with the design.

Your guess on boilers is much closer than the plumbers you have talked to. This should give you an idea as to there qualifications.

Carl

CMadatMe

No Way On Mother Earth

Would I let this guy install my system. How the heck did anyone design a radiant system without a heat loss? Bet they are also going to make the biggest mistake I see out there on combo radiant/hydro jobs, no floor sensors in the rooms having hydro air.



Time to find a competent designer/installer. Anyone can turn a wrench for the most part but the one that does his math shall succeed in providing comfort, efficiency and a properly installed system. Good luck with your choice of contractor..



1,400 sqft of radiant should have a heat loss of around 20K or so. Let me guess he added up the 2 hydro coils capable output, 3 Ton around 55K so there is 110,000 and since very few mfgs have anything in that range he stepped it up to 150,000 btu/hr boiler.

Rich_49

Heat Loss

Heat loss , heat loss . GET IT ?  Are the areas that will have forced air Free of tubing in the floor ?  If I may ask why the 2 areas without hydronic heat after doing the rest of the home with a superior heating strategy ?  Was there no other way to heat these areas ? As Chris stated above if there is tubing in the floor where this air based heat is , you NEED floor sensors .  Where are you located ?    Did not see anyone else mention the fact that you very well may need an HRV or ERV , it would be nice to have some fresh air in this newly tight home . Any heating system sucks when the air is stale and stinky . A proper heat loss can get you in the neighborhood of proper ACH (air changes per hour )  But a blower door test when completed will tell you exactly where you are in regards to ACH Nat and how many more CFM you need to add mechanically .

  Are your domestic hot water requirements very high ? How many people in the home , schedules .  An 80 gallon indirect is large enough for a large family , possibly you could use a smaller unit and store 150 - 160* water and mix down . Yes you can increase your storage capacity w/o increasing tank size  This will insure that when it is really cold out your boiler gets back to Space heating more rapidly .   35 BTU sq ft .  , where are you , International Falls , MN?

Val_LI

Val_LI

Rich,

I wish I could answer all of your questions...but my knowledge in this field is poor.

We are on Long Island, NY.

There are 5 of us (including 2 kids that spend hours in a shower) we all take showers mostly in the evenings.

Areas with forced air are not getting tubing in a floor. no floor sensors.

Areas WITH tubing in a floor will get floor sensors.

Hydronic heat decision came from financial side. we wanted to save money.



The problem is I can not find anybody good enough to calculate heat loss, etc. But anybody can install boiler/WH here.

Val_LI

Val_LI

Can someone give me a rough number? your best guess?

CMadatMe

Call Technical Heating

Bob O'Brien. He should be in the contractor locator here.



http://www.technicalheating.com/

Val_LI

Val_LI

I will give him a call. Thank you, Chris.

Val_LI

Heat Loss calculated!

I downloaded Slant/Fin heat loss calculator and heat loss calculation came to 89,121(BTU/HR).

What Lochinvar Knight Boiler should I choose according to my calculations???

CMadatMe

Heat Loss Is High

A radiant loss is not calculated the same way as the loss for the hydro but 28 btu/hr sqft is workable. I'd do a Vitodens B2HA-28 19,000 - 100,000 btu/hr. You cannot oversize a condensing boiler from the high end. I chose the Vitodens because it will run a 3-way motorized mixing valve for the radiant off its control, has a better HX warranty and better combustion system in my mind. Control is also ready for Vitocom so next year you'll have access to the boiler via an IPhone/IPad/Andriod App..

Val_LI

Val_LI

Viessmann Vitodens would cost more. I'd rather not to go to that direction.



If I understood you correctly, I can not oversize modulating condensing boiler even if I go 150K BTU route, when I only need 89K BTU?

Is this because of modulation feature? Lochinvar has 5:1 modulation.

SWEI

Sizing

Given that the boiler is not actually undersized, the critical factor when sizing a modulating boiler is the ratio of the design heat load of the space to the boiler's minimum output rate (corrected for altitude.)  The higher that ratio, the more accurately and efficiently the boiler will track the load.

CMadatMe

As SWEI

Says, its the low end modulation rate that matters. The only time a condensing boiler will fire to its maximum btu/hr output is when the boilers delta-t is met. That should open a can of worms. As much as some can't grasp it, it's true.. Viessmann is competitively priced against any condensing boiler out there. A B2HA-28 and even the current WB2B-26 are right there.

Rich_49

Val LI

considering you all shower at night you must make sure that the boiler specs meet the demands of your indirect .  If the boiler is not capable of supplying the specified GPM to the indirect and the pump will not handle the head loss through the HX it will not produce as rated . Store the water in the tank high and mix down .  I only mention this because I have seen many jobs where the installer did not understand this and just thought the indirect made what the specs said . Expensive fix and unfortunate for the homeowner .