seeking advice on new propane boiler selection

Consumer123

I have to switch from oil to propane because of an unsolvable chimney problem, and need to go with a high efficiency boiler mainly because of venting considerations. The new boiler needs to serve: 1) hot water baseboard heating to two small rooms that are not used much, but probably need about 30,000 BTUs, 2) a hot water Modine blower used to keep a greenhouse above freezing -- thermostat set at 40 -- there are some tropical plants and a swimming pool/spa in the greenhouse, and the existing 20-year-old blower handles 93,000 BTU, I believe, and 3) a new heat-exchanger pool heater -- for a 7000 gallon pool and adjacent spa. The pool is not used in the heating season, so the boiler will not be being used to for space heating needs simultaneously with heating the pool. I believe I need something like a 140K BTU boiler, though perhaps I can get by with less. The unit that has been recommended is the Peerless PF-140 or perhaps the 110, but I have been spending hours reading online about other brands and wonder if there are similarly priced boilers that might be better for some reason (or as good and less expensive, of course). We also need to choose the pool heat exchanger, and I would appreciate any help with that as well. I have noticed the Triangle Tube Maxi-Flo unit being mentioned, but don't know the issues there either. Many thanks in advance to anyone who gives me any advice.

Ironman

Find a Good, Competent Pro...

And let him select what is best suited for your needs.



Selecting the right boiler is not like buying the best washer/dryer. It's requires hydronic expertise that takes the total system into account. There are few that know how to even do that.



Spend your time researching and finding a qualified pro; he's 98% of the equation.



We install several brands and I always try to pick the one that's best suited to the job.



Also, you may wanna think twice about using the boiler to heat the pool. There are a lot of secondary issues that can arise from that. It can be done, but it may not be worth the effort that it requires to do it correctly. A pool heater may be a better choice. I know you you're probably thinking of killing two birds with one stone, but the long term results may be more costly. Let the pro decide.

Consumer123

find a compent pro -- sounds right

Thanks much for your reply. I'm sure you are right that I am getting ahead of myself trying to understand the various issues on my own. But I do wonder why there would be a possible benefit to separating the pool as a separate load with it's own boiler, as you suggest. Thanks again.

Ironman

It Depends

You hear that a lot around here.



There are several "ifs" that come into play. Here's a couple:



"If" you install an atmospheric boiler, then it's NOT designed to condense. "If" the return water temp from the pool heat exchanger becomes too cool, the flue gasses will condense and that will rot the boiler, flue and chimney. There are ways to controls this, but "if" not done properly you're gonna have an early failure.



"If" you choose a mod/con (modulating/condensing) boiler and "if" it has to maintain 180* water to heat the pool, then your efficiency is going to reduced to about 87% while at that temp. But that can lead to a larger issue: "if" it's vented with PVC, then it's gonna maintain elevated flue gas temps for long periods that the PVC is not made to withstand. A mod/con that sees sustained duty at water temps above 160* should not be vented with PVC. There are other venting materials, but they are more expensive and installers will typically go for the cheaper material because it works in other installations.



These are just a couple, but there are more involving controls, piping strategy, pump selection, etc.



The main thing is viewing the installation from a "total system" perspective and designing from there.



The first step is a heat loss calculation. This is critical to proper boiler selection. We don't guess or size it based on the old one. We do a scientific heat loss calculation. Has that been done? Don't use a contractor that won't do that.