Which boiler?

Dave_4

I've gotten religion, and don't want a low cost inefficient boiler, but it is now a question of size.

I used the free SlantFin download to do the heat loss analysis, and plugged in all my numbers. To get conservative, and not underestimate heat loss, I used an outside design temp of -35F.

It was -27F here a few mornings ago, and I've seen it go to below that.

Problem is, going conservative with my heat loss analysis, I only am coming up with about 59,000 ButH heat loss. This, for a 3 br, 2 ba house, one woodframed floor above a walkout finished basement level, the basement done with ICF walls, except for its end walkout wall.

Looking at the WM Ultra, Triangle Tube Prestige, and Buderus wallhung, I am not seeing boilers available below input ratings of about 80M.

What to do? I don't want to over-boiler this. Aren't there drawbacks to having too much boiler?

ALH_4

Not much choice

The HTP Contender and Munchkin are the only mod/con boilers currently available in that range. HTP boilers are built with budget as the priority. Maybe soon there will be another option in this range.

Uni R_3

Heresy and Modcon Sizing

Gene,

Sizing first. Look at the minimum modulation number when comparing boilers (you might also want to note when any boilers have their min rpm raised at the suggestion of the mfr to run better - what that rate becomes).

The top end can always be limited downwards but the bottom end is the bottom end. That said, modcons don't suffer the same sizing issues as conventional designs. The flue temp and condensing concerns of oversized atmosperic boilers don't exist. When modcons can no longer modulate their gas valves lower they modulate their firing time intervals - all without you really knowing it. Yet when you want hot water for showers or whatever via an indirect fired water heater - boom, the capacity is there and ready.

That said, please now call me a heretic because as much as I love the concept of hydronic heat, I can't help but think forced air might be better for a retreat style home. If nobody is there for extended periods of time, the damage potential of freezing and leaks are greatly increased. In addition, I think forced air's better for doing a quick warm up if the place is just used on weekends. A well dialed in modcon typically has zilch or next to zilch left for recovery if dialed to the outdoor rest curve.

I'm gonna wash my mouth out with soap now...

ALH_4

control

I would absolutely run 30% propylene glycol in the system.

I must admit my ignorance as to the controls in these boilers, having worked with the Vitodens almost exclusively. Is there an "external change of heating program" in the control so they could run a global setback when no one is there and crank it when they show up simply by flipping a switch or dialing in with the phone?

Dave_4

This one?

So, if my numbers get confirmed by the couple sources I've asked to run heat loss with their software, would you say the Munchkin Contender MCA80 with its low-fire 19M and high at 80M will do the job?

My numbers showed a total loss at -35F as in the range of 59M, if I recall correctly.

Dave_4

Antifreeze

We've had our heating guy here do that for the high end housing we have done, and would certainly do it for this small job.

ALH_4

boilers

Short of a Lochinvar Knight, WM Ultra, or Vitodens, I think the only 80MBH boilers are the HTP models. I don't think the smallest Baxi is available in the US yet. As Uni mentioned, it is the low number that starts to be disappointing as the heat load drops. 59MBH loss is pretty low compared to the output of the boilers on the market today. Unless you are willing to jump to the price of the Lochinvar or WM, I think the Contender is the only choice left.

Someone please correct me if I am wrong.