Mod-Con HWHs: When Can They Be Used As Boilers?

D107

Several fine contractors have recommended installing a mod-con hwh as a boiler for my 40-50Kbtu NY home. (Versa Flame is one suggestion.) Seems to cut down considerably on installation costs since the unit serves as a boiler, hwh and buffer tank all in one. And because of the buffer tank function, oversizing it a bit--if smaller sizes are not available--seems not so critical since it would not be short cycling. I'm assuming these type of units are every bit as rugged as mod con boilers in terms of handling the duty cycle.

D107

I should also verify if its buffer tank function obviates the need for super-close load-sizing.

SeymourCates

Versa Flame is no longer in production.

The pressing question that must first be answered is what SWT is required at design to produce the required 40-50K output? Only when that is determined can a decision be made to use a HWH rather than a boiler/indirect combination.

D107

You're saying that in certain situations boiler/indirect would work and hwh wouldn't? Have to do with type of emitters? Are hwh usually used with underfloor radiant heat? In our case two of three heated floors are mostly oversized cast iron; basement has 30ft of baseboard which I'm contemplating converting to cast iron baseboard or radiators. House has been fairly well insulated. About VersaFlame, I was told despite its being discontinued, the components can be put together.

Paul48

@Rich ........Maybe he will respond. He has a good relationship with HTP

SeymourCates

If you need a SWT of 180F at design, a HWH would be a poor choice.

Versa Flame, if available, offers that capability but you'd be storing a lot of water at elevated temperatures just to make DHW via the FPHX.

A HWH can be an economical choice when coupled with a FPHX for CH (Versa Hydro) provided the building can be heated with reduced SWT (160F max in the case of Versa Hydro.............145F max with a traditional HWH).

D107

The expectation is that SWT would be lower than 140 at design. As for hot water, we've been fine (two people) with a 50 gallon HWH that fires at 30Kbtu, set at 140degrees with mixing valve down to 115-120º.

SeymourCates

I would utilize the HTP Phoenix light duty HWH with a FPHX to supply the CH requirement. Keep the Phoenix at 150F for the coldest months and lower it to 130F for all other periods.

Economical and efficient.

D107

If heating supply temp is 150º and return temp is 130 then it's considered condensing, yes? (Heat loss is really likely closer to 30Kbtu but I used 40-50kbtu just for some headroom.) So that sounds good.

SeymourCates

Well, it's on the ragged edge.

Here is the efficiency curve for the Lochinvar Knight. Consider it typical.

http://www.lochinvar.com/_linefiles/Knight XL Efficiency Curve-2013.pdf

You really don't get serious with regard to the efficiency until the RWT drops below 100F. That's very difficult to accomplish. However, each time you draw DHW, the makeup water (supply) is well below 100F.

Rich_49

Pioneer with FPHX = Versa Flame . Standby losses are miniscule . Seymour Cates may not be aware but myself and another long ago site visitor designed a very nice system in the case it was ever a good fit in the absence of the Versa Flame .

that idea was in case the system required higher water temps . If higher temps are not required the Phoenix or Light Duty with FPHX would be considered .

Once someone visits the home and performs a heat loss calc we can really discuss this with some substance , until then we're all just guessing . Gonna refrain from commenting further since David has contacted me awhile ago about performing the heat loads / design and possibly having Ezzy T do whatever work is required . Do not wanna muddy the waters or influence open discussion . have at it folks .

Zman

@David107
If you have the means to follow @Rich 's recommendations i would highly recommend that path. He is very knowledgeable and has tons of HTP experience.

D107

@Zman yes, thanks, we have 'met' on the phone and have had some great discussions. I'm looking forward to the process.

Paul48

The reason I called @Rich , is that he has the most knowledge about HTP products of anyone I know. With Rich and EzzyT, you've got quite a team. I'm a homeowner with a mechanical background. I've seen samples of both their work. They would be my choice.

D107

Yes, I am very impressed with both his knowledge and creativity. As we go forward I am developing a set of general criteria for any jump from my current old atmospheric to mod-con hwh-boiler-buffer tank:
1. Does such a setup have same durability as mod-con boiler and indirect hwh?
2. What is track record in the field for the specific model's performance over time?
3. Are parts readily available at reasonable prices?
4. Are annual maintenance AND repairs relatively simple for local contractors to handle?
5. Will complexity of system--with variable speed circs etc––lead to more repairs?
6. Does the buffer tank aspect reduce the need for an optimum match between firing rates and heat loss, since short-cycling would not occur?
7. Given that heat and hw will be from a single source--as opposed to my current stand-alone gas hwh--would I need to invest in some kind of generator or backup battery system for boiler down time or loss of power?
8. Will unit work well with hard water with chlorides?

ROI is not that high a concern, though I'll certainly make comparisons for overall price tag and economy over time. My current 36 year old boiler and old flue might well last another ten years--but it might not; my 10 yr old hwh I'd otherwise change out in a year or so. I'd rather not do these changeouts in a rush in mid-winter with the nearest installer who happened to have the time.

NY_Rob

David107 said:

....Are parts readily available ..

Good question to ask your installer (if he's selling you the HWH), or the supply house if you're buying it direct.
If your looking for same day replacement parts.. I can almost guarantee you the answer will be no.

David107 said:

.... at reasonable prices?

If you're referring to HTP, spares seem to be reasonably priced- $6 for a flame sensor, $226 for a main board for the UFT-80W.

D107

@NY_Rob thanks. I'd never try to buy any heating equipment--that's for the contractor. Of course one can stock up on some parts...I just added #8 criterion: can unit work with hard water with chlorides?

NY_Rob

^ The Water Quality Requirements can be found in the install manual for the boiler or HWH.

Paul48

@David107

So.........You're asking every question you should be asking the contractor, in an open forum? At some point, you have to trust your contractor. Realize that if you ask a group of people their opinion about anything, you will not get complete agreement. I can't see how this helps you with the vetting process. I understand wanting to be careful. Look at their work. Talk to references.

D107

@Paul48 I understand that opinions vary; but I've found that on this site different opinions are helpful in helping accumulate enough knowledge to make an informed decision. I'll never come near knowing or try to know what Rich and many of you guys know. When I have him down to do the heat loss many of those questions will better be answered. From preliminary conversations I can already say that I have great trust in the design and installation expertise; it's the equipment and future maintenance issues that concern me more.

Paul48

Those are different issues, but they are still "trust" issues. You need to trust that those guys will treat you the same way they would treat family. They take pride in their work. Have you seen examples of their work?

D107

I always ask for photos of a contractor's work; as you say most are proud to show them. Suffice to say that the Wallies that I've met or done business with are such a breath of fresh air compared to the rest of the competition--full of great curiosity, knowledge and passion for their work.