New residential construction HVAC for basement
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We are developing plan for building a one-level home (2200 sq ft) with walk-out basement (900 sq ft; Insulated Concrete Forms) in Kentucky. Was planning on placing radiant/hydronic heating in floors powered by a Polaris Water Heater that is designed specifically for domestic water production and space heating. Would like to confine HVAC/AC to only the first-level (not basement) but am concerned about need for internal ventilation of basement. Avoiding geothermal system due to price. All ideas and input is appreciated.
Bill & Petra
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You need ventilation on both levels. If you're combining the ventilation and a/c ducts for the main level, your cheapest option is probably just adding ducting to the basement. Only other real option is to have separate ventilation and a/c systems.
Note that in floor heating is not really recommended for well insulated houses (I made this mistake). Maybe look into using ductless mini-splits for heating and cooling, plus a fully ducted HRV or ERV.
Mr. Lambert, thanks for taking time to respond. As follow-up to understand, I'm planning for the radiant hydronic heat to be placed in floors in basement and on the 1st level to include a garage, all zoned, I think? Does this change your recommendations? Also, how does one determine whether to use a fully ducted HRV or ERV?
First, let me say I am a lay person, not an HVAC professional, so keep that in mind.
The issues with radiant in floor are cost, response time and expectations.
Most people expect heated floors will provide a warm feeling on their feet. This will never happen in a well insulated house, because if the floor was warm enough to actually feel warm on your feet, your house will be uncomfortably warm. The "warm floor" phenomenon is an effect of a bygone era of drafty, poorly insulated houses. There is often an expectation that heated floors will save money because you can set the ambient temperature lower (note how this is in complete contradiction with the "warm floor" expectation, yet people often hold both of these ideas simultaneously). There's actually no evidence for this. I can understand why people might think it's true. In my new house, I am quite comfortable in shorts and a t-shirt with an internal temperature of 18.5C, whereas in my older house I would be chilly at 20C. However, this has nothing to do with the in floor heating. I am experiencing the same comfort at 18.5C right now, and the in floor heating hasn't been on for months. It has to be a product of the super insulation and air tightness.
Radiant floors take a long time to change the temperature in the room. This is true whether there is a large thermal mass (e.g. concrete) or not (e.g. wood sub-floor with staple up fins). This may not be a huge issue for you, but it's definitely a limitation worth noting. If, for whatever reason, you decide you're chilly, you need to put on a sweater. Even if you think you're going to be chilly 3 hours from now, just get that sweater out of the closet. You need to either just be happy with a wider variation in temperature, or planning temperature swings at least a half day in advance.
Hydronic in floor heating systems cost more than equivalent other systems. Given that, it seems like they would need to offer significant advantages in order to be justified, and in most cases there just aren't many advantages.
From a performance standpoint, a fully distributed ventilation system is the gold standard. Start from there and see if you have a good reason not to do it. Energy recovery, whether ducted or not, is a must for any efficient house, excepting if you live in a climate with minimal heating/cooling needs.
I don't know of any Polaris that is specifically designed for space heating. Many heating systems have been built around them, but they tend to be prone to short-cycling unless the control board is modified (violating the warranty) to provide more high to low temperature hysteresis.
HTP's Versa series IS specifically designed as a combination appliance suitable for hydronic floor heating. Their Phoenix series is designed for use with hydronic air handlers/coils, but like the Polaris would need an isolating heat exchanger (for health safety) if used with a radiant floor.
Any of these solutions are extreme overkill for the low heating loads of an insulated walk-out basement, but if it's heating the upstairs too it's easy enough to zone. Like the rest of the series, the HTP Phoenix Light Duty has a modulating burner (unlike the Polaris), that at even at minimum fire would still have some margin for most 2200' ICF houses, with more burner capacity left over for domestic hot water than a standard 50 gallon water heater. I believe the smallest burner Polaris is ~100,000 BTU/hr, which is extreme overkill for space heating even a code-min house. The Phonix LD maximum is ~75,000 BTU/hr, but it can throttle back to ~25,000 BTU/hr.
As an HVAC solution for just the basement, a cold climate half-ton or 3/4 ton mini-split heat pump can heat most insulated 900' walk out basements at 0F.
The first order of business prior to designing/specifying any HVAC solution is to calculate the 99% heating load and 1% cooling load room by room, zone by zone. Only then is it possible to narrow in on the optimal solutions. Without knowing any of the details it's impossible to say whether your whole-house heat load is going to be 15,000 BTU/hr or if it'll be 30,000 BTU/hr but it's unlikely to be over that 30K number without leaving some windows open. Get a Manual-J load calculation from a competent third party, not an HVAC contractor- somebody who makes their reputation and living on the accuracy of their numbers rather than making it selling/installing/maintaining HVAC equipment.
Mr. Dorsett:
Thanks for a well thought out reply. I'm still unfamiliar with much of the technical jargon. I will certainly get a Manual-J load calculation done. In regards to your comments, I was intending to place hydronic radiant heating on both levels (1st level and basement) of the home to include a workshop floor. Does this change your recommendations?
If going with two zones of radiant in a better than code house designing it around a Phoenix LD water heater would still work just fine, and doesn't change the recommendations a bit.
The heat loss of a tight 2200' of the fully above grade part of an ICF house without excessive expanses of code minimum window would be usually be less than 25,000 BTU/hr @ +10F (a typical 99% outside design temp in KY.). An additional 900' of walk-out basement in the same house would be no more than ~5,000 BTU/hr.
So worst case whole house heating needs ~ 30,000 BTU/hr of burner output which is less than 1/3 what the smallest Polaris' burner puts out. So it's going to do a LOT of cycling on/off even if you hack the electronics to limit short-cycling (burns shorter than 5 minutes multiple times per hour). It's just too much burner.
The Phoenix LD puts out more than twice the 30K number at max-fire, so you'll still have plenty for domestic hot water even with both zones calling for heat, but it's modulating burner will turn down to about 25,000 BTU/hr, which means it will have far fewer efficiency-robbing on/off cycles when serving space heating loads if set up correctly.
A cold climate ductless mini-split could easily cover the load of the walk-out basement. The half ton Mitsubishi FH06NA can deliver as much as 8000 BTU/hr @ +5F, but can still modulate down to 1600 BTU/hr @ +47F. A 3/4 ton Fujistu 9RLS3 is capable of delivering more than 10,000 BTU/hr @ +5F and can throttle back as low as 3100 BTU/hr @ +47F. As with fossil burners, frequent cycling takes a toll on efficiency, so the unit that can modulate over the widest range but still covers the design heating load is usually going to be the most efficient, as long a the compressor types are comparable. These things can cool & dehumidify at high efficiency too, which can could be a factor in what you choose to heat with. In heating mode they don't deliver warm toes, but they deliver very stable room temperatures and are virtually silent compared to an average window-shaker AC unit (quieter than most refrigerators.)
We built our home with everything we need on the main level with a full basement underneath that is mostly a work shop. We designed the basement as a semi conditioned space The HVAC equipment and ductwork is in the basement with 3 register in the basement that have never been opened. The basement air is the same temp as upstairs. The concrete floor is a little chilly if you are bare footed but since I wear shoe in the shop it make no difference. The upstairs wood floors are not cold. The variable speed air source heat pump has worked well for us.
If you will need a construction loan be aware the banks appraiser will give you zero added value for your expensive HVAC system over cheapest electric base board. The same goes for your ICF walls, heavy insulation and good window.
Walta