Hydronic Heating and Boilers in Arvada, CO: Sizing by Era

Aug 26

7 min read

The right boiler for a house in the original blocks around Olde Town is close to the wrong boiler for a house built in the last fifteen years on Arvada's west side. Same city, same weather, same gas at the meter — opposite answers. The old house wants a large amount of heat delivered gently and continuously into a structure that stores it. The new house wants a small amount of heat delivered without the equipment tripping over how little it actually needs.

So before you call anyone, figure out which of those two conversations you're in. Arvada makes that harder than most places, because the city holds an unusually wide span of building eras inside one set of boundaries: a small historic core, an enormous stretch of post-war tract housing, and recent subdivisions out west built to envelope standards that didn't exist when the rest of the city went up. A rule of thumb that works on one of those houses will fail on another, and the failure mode isn't the one most people expect.

Which Arvada house are you actually in?

Three rough groups, and most houses fall cleanly into one.

The first is Olde Town and the original residential blocks around it — the oldest and densest part of the city, built long before insulation was something a builder specified. If your house has masonry walls and plaster interiors, you're in this group.

The second is the largest by a wide margin: the post-war decades through the 1970s, single-story and split-level houses on modest lots, block after block of them. Insulation exists in these houses but it was never generous, and what's there now depends entirely on what previous owners did about it.

The third is the western and northwestern edge of the city, where substantial recent building has happened. Homes built there in the last fifteen years are sealed and insulated to a standard nothing else in Arvada was held to. Building requirements for insulation and air sealing tightened repeatedly across that century, which is why a newer Arvada house needs materially less heat per square foot than an older one of exactly the same size.

Put numbers on it, because the gap is the whole point. On the Front Range, an older brick house with some weatherization runs around 40 BTU/hr/ft². Newer tight construction runs around 25. Two 2,000-square-foot houses, one on each end of Arvada's timeline, and one of them needs something like a third less heat than the other on the coldest day of the year.

Why does an older house near Olde Town want steady, low-temperature heat?

Because heavy houses respond slowly, and fighting that is a losing game.

A masonry house has real thermal mass. The walls absorb heat and give it back over hours. That mass is why these houses feel stable when they're heated well and clammy when they're heated badly. The wrong approach is short, hot blasts — the air warms, the thermostat is satisfied, the burner shuts off, and the walls are still cold and still pulling heat out of the room. You get temperature swings and cold spots that no thermostat setting fixes.

The right approach is longer run times at lower water temperature, matched to what the building is losing at that moment. A modulating condensing boiler does this well when the system is designed for it — but only if return water gets below about 130°F, which is the entire condition for condensing. Above that, it's running around 85% and you've bought a feature you never use. That's also the one place where old emitters bite: cast iron radiators originally sized for 180°F water can't deliver their rated output at the 120–140°F a mod-con wants, so the emitter side has to be evaluated before the boiler is chosen, not after.

One more thing specific to older houses here: if the boiler shares a masonry chimney with a gas water heater, pulling the boiler off that stack can leave the water heater unable to draft, and that gets solved as part of the job, not discovered afterward.

Why is a recently built west-side house the harder heating problem?

This surprises people. The newer house is easier to keep warm and harder to equip correctly.

A tight, well-insulated house has a small design heat load. Small enough that on most winter days it isn't asking for much heat at all — and small enough that a lot of the equipment sitting on supply-house shelves cannot run slowly enough to serve it. The house doesn't need a bigger fire. It needs a smaller one, held for longer, and that turns out to be the harder thing to buy.

When the equipment's lowest possible output is still more than the house is losing, the boiler has exactly one move: fire, overshoot, shut down, wait, repeat. All winter.

What is short cycling, and what does it actually do to a boiler?

Short cycling is a boiler that starts and stops far more often than it runs. Not a nuisance — a wear mechanism.

Every cycle has a cost. A pre-purge and post-purge that push heat out the vent. An ignition sequence that loads the igniter, gas valve, and flame-sensing circuit. A thermal swing across the heat exchanger — expansion and contraction on every single start, which is exactly the loading that cracks things over time.

The practical summary: boiler life tracks cycles more closely than it tracks hours. A unit that fires eight times an hour all winter ages far faster than one that runs long and slow, and it delivers efficiency well below what's on the rating plate while doing it. It also beats up the circulator and stirs the system water, and system water that's been stirred and neglected turns into the black magnetite sludge that ends circulators early — there's a five-minute check for that.

Why do the newest houses get the wrong equipment more often than the oldest?

Because the smallest boiler most contractors stock is bigger than a tight house needs, and because square footage is a seductive substitute for arithmetic.

Nobody sets out to oversize a low-load house. It happens because the house is 2,600 square feet, the mental math says a house that size needs a certain size boiler, and that number came from a housing stock built decades before this one.

The old houses in Arvada rarely have this problem — their loads are genuinely large and most equipment can serve them. It's the new construction out west where the load falls off the bottom of what's available, and where the answer means choosing for minimum output rather than maximum, sometimes adding system mass so the boiler has somewhere to put heat it can't avoid making.

If you want the arithmetic laid out at metro scale, we've written about how boiler sizing goes wrong across Denver.

Call (303) 908-5658 or use the contact page and we'll tell you which of these two conversations your house is in.

What does turndown mean for a house with a small heat load?

Turndown is the ratio between a boiler's highest and lowest firing rate. A boiler rated at 120,000 BTU/hr with 5:1 turndown throttles down to about 24,000 — and no lower.

Now take a tight 2,000-square-foot house on the west side at roughly 25 BTU/hr/ft². Design load is around 50,000 BTU/hr, and design load is the coldest hour of the year. Most of the winter that house is asking for a third of that — call it 17,000. The boiler's floor is 24,000. It physically cannot meet the house where the house is living, so it cycles from November to March.

That's why the specification conversation for a new house is about the bottom of the range, not the top. Wide turndown, correct minimum fire, adequate system volume, and a control strategy that lets the thing run.

Does being at roughly 5,340 feet change the sizing math?

It does, and it's a common place to get sloppy. Combustion equipment loses capacity in thin air, and manufacturers publish altitude derate tables for exactly this reason. Arvada sits at roughly 5,340 feet.

The derate gets applied once. Not zero times — that leaves you short on the coldest day. Not twice, which some equipment already accounts for internally and which pads the number all over again. And it applies across the firing range, not only at the top, which is one more thing to check on a low-load house where the minimum output is what actually matters.

What about the mid-century houses in between?

This is most of Arvada, and it's the group where the era alone tells you the least.

A single-story or split-level house from the post-war decades started life modestly insulated, and everything since has been optional. One has had the attic brought up and the windows replaced. The one next door hasn't. They look identical from the street and their heat loads can differ by a third.

Split-levels bring their own issue: stacked half-levels stratify, heat collects up top, and one thermostat in the middle tries to represent all of it. That's a zoning and distribution question more often than an equipment question, and the two are worth separating before you spend money on the wrong one.

How does the real heat load get established instead of guessed?

A room-by-room heat loss. Not square footage times a number someone remembers.

That means walking the house and actually counting: wall construction and what's in it, attic depth, window count and type, orientation, exposure, air sealing, and how the existing distribution is laid out. The output is a number per room and a total for the house, and that total drives everything downstream — boiler size, minimum fire, the water temperature the emitters need, whether a buffer tank belongs in the design, and whether a condensing boiler will ever see return water cold enough to condense.

Same procedure on a masonry house near Olde Town and on a new build out west. It produces very different answers, which is the point of doing it rather than assuming. The same measurement drives radiant floor design, where getting water temperature wrong is permanent rather than adjustable.

We do this before quoting equipment on boiler installation and replacement, and it's the first thing we'd do at your house too.

Who permits and inspects boiler work in Arvada?

Arvada runs its own building department, so permits and inspections go through the City of Arvada rather than Jefferson County.

Where do you work?

ByDesign Hydronics & Air is based in Littleton and works across the Denver metro, including Arvada. We're a hydronics-only shop — boilers, radiant floor heat, snowmelt, and mechanical room design — which is a deliberate limit, not a gap. If your project is outside what we do or outside where we can get to, we'll say so and point you elsewhere rather than stretch. You can see the full list on our services page, or read more about how we approach hydronic heating in Denver.

If you want a straight answer about what your Arvada house actually needs, call (303) 908-5658 or reach us through the contact page.