boiler choice for small house

gennady

Zoning boilers on outdoor reset with pumps or zone valves?
I would never do that.

gennady

How would you get to the zone temperature setpoint after setback with low water temperature coming out of the boiler without the boost? it will take quite a time.
I would not even mention other issues related to zoning.

gennady

So, you are using zone valves and zone thermostats as a high limits?

gennady

I prefer TRVs with VFD pump to zone valves with thermostats.

gennady

Very easy. I do it all the times by installing by-passes with TRV.
I convert series into parallel.

CMadatMe

On another note - The CU3A will also control a variable speed system pump via 0-10 so that pump flow rate matches modulation rate if either of you were not aware of it.

gennady

It would not be me spending money. It is client the one who invests money in the comfort and convenience. I just give them this option. As a matter of fact I lost many jobs just because I did not want to do things I do not believe in. But it is just me.

gennady

TRVs with by-passes resolving:
balancing issues
radiators sizing mistakes
take into account room heating gains
remove short cycling
allow to deliver exact amount of heat to the right place at the right time.

I understand when contractor does what customer wants, but does customer knows what he wants if he is not given options with explanations?
And why contractors are thinking that price is the main criteria for contractors choice by HO?
Are we discounting our profession?
But this is another topic.

BigRob

Our WHN199 heats our twelve unit condo building just fine in San Francisco. Each condo is about 1000sf. The min fire short cycled when the thin slabs get to temperature, so we added a high limit delay. If I had been more involved when the install was performed I would have got a tank based mod con. They make a lot of sense for the random 2 or 3k btu load if you can handle lower temps. Currently, we have the WHN199 with a SEP4 feeding the heat and a KBN286 with TT indirect through a tempering valve for HW. Our boiler room is really a closet - about 2.5 doors wide, so it's all stuffed in there. A HTP tank based mod con system would be so much simpler and take a lot less real estate for DHW and hot water. Based on my experience, a 199 model would probably heat our entire building and hot water. We don't have the extended cold snaps out here by the water.

Paul48

Before considering any mod/con, you should do a radiation survey, room-by-room. You need to have sufficient baseboard to allow lower supply temperatures. Baseboard manufacturers have charts that specify their output at different supply temperatures. If your home has just enough baseboard to properly heat it at 180* supply, you will never see the efficiency a mod/con can provide.

bob eck

Paul if the home has copper baseboard or duct coils and other Heating units that require 180 degree water temp on design day yes a condensing boiler will not condense. But design temp in most cases are limited days and there are many days in the shoulder seasons and in the middle of winter that are not near design temp. For jobs like this look at using the HTP Pioneer condensing gas boiler with a 55 gallon storage tank. This gives the heating system water volume and will help to keep the boiler condensing longer even in the dead of the winter Heating season. Great for jobs with small zones.

Paul48

@bob eck

That's a great product. It doesn't fit in all applications, and , even with incomplete information, some might argue that it doesn't fit in this one. It has a minimum modulation of just over 30k btus, which exceeds the heat loss of the structure. More information is needed to properly guide this person. Now would be the time to address imbalances and insufficiencies, if they exist.

Sweetheart

I'm baaaack...

When I discussed the oversizing concerns with one of my original three contractors, he asked this week if I would be interested in a Navien NHB-80. This sounds more reasonable at 80K BTU/hr but with a 10:1 turndown ratio, making its range 8K-80K BTU/hr. I would think the low end would minimize short-cycling when outdoor temps are moderate while the high end would be more than enough for DHW.

Any opinions on this unit?

I am meanwhile awaiting a proposal from a fourth contractor.

NY_Rob

The Navien NHB-80 uses primary/secondary piping which requires a dedicated boiler circulator in addition to the system circulator and indirect hot water tank circulator. Being that a mod-con can circulate it's low temp heating loops up to 20hrs/day or more- that extra pump (Taco 007 recommended per the Navien NHB-80 install manual) running 20+ hrs per day can really add to your electric bill.

If you're going to go with a 80K BTU 10:1 turndown mod-con, take a look at the HTP UFT80 (or Westinghouse UFT80W- same boiler just branded/sold under the Westinghouse label) which does not require primary/secondary piping and the additional circulator for the boiler loop.

Sweetheart

I just made a decision - not a perfect one, but hopefully adequate. I'm going with the Navien NHB-80. Had a proposal for the HTP, at a higher but not prohibitive cost. One contractor seems very good, the other excellent.

The HTP seemed a no brainer, except: The very good contractor, who proposed the Navien, is closer to my house and has much lower service rates. For up to 10 years, they warranty all work if I get their reasonably-priced service visit once a year.

Both contractors were well-recommended for making sure the job is done right and the customer satisfied.

Thanks for all for your comments. Never thought a heating forum could be entertaining too!