Furnace replacement

[Ken Tannenbaum1]

I've got a 20+ yr old Becket furnace, just tuned up and running at 83% efficiency. Our house is circa 1890 and I feel close to that, in forced retirement. The house gets heat fine but we're in the Hudson River Valley and winters are cold. I can research what's a good replacement for oil and the delivery company will gladly install a new one, BUT, I'm trying to save. The question is, does it make ANY sense to buy a well researched furnace and hire a plumber to install? While I'm here, glad to get advice about a good brand.

Thanks very much. Ken

 

[Dana]

Is it a furnace (= hot air distributed in ducts) or is it a boiler (=steam, or pumped hot water.)?

Is oil your only fuel option? How old is the tank, and is it showing any signs of rust from condensation?

To assess the burner size requirements, does your oil vendor stamp a "K-factor" on the end of the slips? If yes, what are the K-factors for mid and late-winter oil fill-ups? If not, how much oil do you burn through in a winter? Almost all installed heating equipment in the northeast is ridiculously oversized for the actual loads, which leads to lower as-used efficiency and lower comfort. AFUE testing presumes 1.7 x oversizing factor, but ASHRAE and others recommend no more than 1.4x oversizing for optimal comfort while retaining margin for outdoor temps much lower than the 99% temperture bin, and enabling overnight setback strategies, etc. So knowing what the actual load is important.

A K-factor is the base-65F heating degree-days per gallon, so with that and the tested combustion efficiency of the burner we can work backwards to get a fairly accurate estimate of the heat load at any arbitrary outdoor temp. The 99% temperature bin in Catskill is something like 3-5F (only 1% of the hours in a year are colder than that), so designing around the calculated heat load at 3F would be a perfectly appropriate starting point. If you do that even a 1.25x oversizing factor would still have you covered at -10F, a common enough absolute winter low, and a 1.4x oversizing factor would cover you down to -20F, a very rare once in a century temp in Catskill,NY. Most heating systems in the region are 2-3x oversized, as if the designers were anticipating -150F temps or something.

Rather than buying the equipment and hunting around for a cheap installer, it's best to characterize what you need VERY carefully, possibly specifying the specific model & size, then putting it out to competitive bid. By doing the leg-work ahead of time you save design & sales time for the installer, and would be able to discuss the particulars of the heating system intelligently. You'd also be able to weed out the worst proposals quickly and focus on those who have a better handle on what they're actually doing. It's sad to say, but there is a fairly poor average state of system design competence in the HVAC biz.

 

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[Ken Tannenbaum1]

Dana...great reply, comprehensive, thoughtful. Appreciate it.

What I can stipulate is that the boiler supplies hot water to baseboard radiators downstairs and for household use.
There's propane for the stove and electric 220 baseboards I installed in the bedrooms upstairs.
I foolishly wasn't thinking last year when I decided to replace the very old oil tank in the basement...so that's new, otherwise this could include talking about using gas instead of oil if/when the boiler gets replaced.

As for your comment about overbuilding HVAC systems and many guys not having a real good idea of what's the right size, etc. I do get what your saying. I'm not at the house and won't be for a week, so I can't get to a delivery slip to see about the K-factor. That said, I thought these things were based on geography + sqft of the property to help determine size requirements. If that in any way is useful, the ground floor is what gets heat from the boiler (about 1000 sqft) and the house is in Catskill, NY, which you already know. Sadly, what you said about weeding out the bad proposals is important. I'm in the service end too...a photographer...totally different but the same in some ways. Not all photographer are created equal or paving guys or carpenters or plumbers, etc. In Catskill, that became crystal clear a long time ago.

Last thing, about the oil tank, I got three bids last year, the best was from the oil delivery company and they did a clean install in a lousy space, my basement. They gave a me a rough number for the boiler at the time, about $8000, which freaked me out. So in planning for the future I thought I'd come here and ask the question I did. Maybe I'll be best off dealing with them...just haven't decided. Meanwhile, Terry Love did a great thing establishing the forum...it's aces. Again, thanks.

 

[Dana]

Heat loss is through the exterior surfaces of the house (the windows, roof, exterior walls, foundation, etc), and air leakage. This is not a function of the square feet of living space, since the same sized house can have radically differing amounts of exterior surface area, with differing amounts of insulation and air leakage. HVAC contractors get used to using simple rules of thumb based on the square footage, but those rules of thumb have HUGE margins in them. They'll often use an even more generous rule of thumb for antiques like yours.

Geography only matters in terms of the historical temperature statisitics. The bigger the difference between indoor and outdoor temps, the greater the heat loss. The true professionals would use the 99th percentile temperature bin for that location when running a calculation based on the characteristics of the construction, the R-values & U-factors, etc.

That said, an insulated somewhat air-leaky framed house with clear-glass storm windows and NO foundation insulation typically comes in at about 25-30 BTU/hr per square foot of conditioned space at an outdoor temp of 0F. If the foundation is insulated, the wall cavities have some fluff in them (and the attic too), it'll usually be in the 15 BTU/hr-ft^2 rang @ 0F. Either way, even the smallest oil boilers are probably oversized by at least 2x for the load, but we'll figure that out when you get the billing info. If there is no K-factor, a few successive bills with exact dates & quantities would suffice- we can look up the weather data on degreedays.net. But the odds are you're looking at no more than 30,000 BTU/hr, and possibly less than 20,000 BTU/hr. The smallest oil boilers are in the 50-60,000 BTU/hr range.

The other important factor is to measure up the radiation (by zone, if multi-zoned), since that may affect the boiler sizing.

For about $4000-5000 you could install a 1.25-1.5 ton ductless mini-split heat pump with over 20,000 BTU/hr of capacity @ 0F, and it would cost less to heat with than heating oil (unless heating oil takes a real dive for awhile, which it looks like it might, if Iran starts pumping faster and China's demand keeps slumping.) That would also provide high efficiency air conditioning to boot, but it's point-source heating (like a wood stove), and doored-off rooms might be too cool in winter. There are mini-ducted versions that could work too, but that would end up in the same $8K range. But we'll keep those alternatives on the back burner until we know the real load is.

 

[Ken Tannenbaum1]

That is a bucket of info. As mentioned, I can't get to the data until the weekend following this one.
When I do I'll be back. For now however, your thoughts on the effect of China and Iran's behavior, much as I follow that stuff, won't determine what I do, as you may imagine. As for the ductless heat pumps, I hadn't thought about that and now will. You're right, the house is an antique (not that it's a high value antique!!!) and only the three bedrooms have A/C's and they are rarely used. So I don't think the utility of a mini-spit unit makes sense...but that's said without hard knowledge of them. Doesn't sound right for my place. Plus, point source heating's not for me. We have a wood stove in the living room and use it more as a poor man's fireplace when I crank it up.

 

[Jadnashua]

Humidity levels in the Catskills can be nasty, even if the temperatures aren't all that high! If you have any issues with allergies, an a/c unit can be a godsend! One of the modern split systems can be quite efficient.

 

[Dana]

There are ducted mini-splits that work at your local temps that may have sufficient output for your loads, if point-source heating doesn't work for you. A Fujitsu -18RLFCD is good for about 20,000 BTU/hr, and would probably cover it if the house is reasonably tight. It's about 10-15% less efficient than a the best-in-class point-source types, but still higher efficiency than what was the state of the art 5 years ago.

The COST of heating with mini-splits has been less than half the cost of heating with oil at recent years' electricity & oil pricing, and the up-front cost of the installation can be less than a new oil-boiler, even for ducted version, for a single floor with a basement below it that can be used for routing the ducts. The reason to get away from oil is to get away from the price volatility (and the local PM2.5 emissions for some folks.) Even if you never run it in air conditioning mode it can be worth it.

But the fact that you have three window-shakers means you probably WOULD use it in air conditioning mode if you had it, and it would be 2x as efficient as a window AC unit, and quieter than your refrigerator.